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  • 1. Abellán, F. J.
    et al.
    Indebetouw, R.
    Marcaide, J. M.
    Gabler, M.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spyromilio, J.
    Burrows, D. N.
    Chevalier, R.
    Cigan, P.
    Gaensler, B. M.
    Gomez, H. L.
    Janka, H. -Th.
    Kirshner, R.
    Larsson, J.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Matsuura, M.
    McCray, R.
    Ng, C. -Y.
    Park, S.
    Roche, P.
    Staveley-Smith, L.
    van Loon, J. Th.
    Wheeler, J. C.
    Woosley, S. E.
    Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L24Article in journal (Refereed)
    Abstract [en]

    Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks (nickel heating). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

  • 2. Alp, Dennis
    et al.
    Larsson, Josefin
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gabler, Michael
    Wongwathanarat, Annop
    Janka, Hans-Thomas
    X-Ray Absorption in Young Core-collapse Supernova Remnants2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 175Article in journal (Refereed)
    Abstract [en]

    The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is 100 t(4)(-2 )E(-2), where t(4) is the time since the explosion in units of 10,000 days (similar to 27 years) and E is the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity at similar to 1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than that in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of similar to 100 L-circle dot on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.

  • 3. Alp, Dennis
    et al.
    Larsson, Josefin
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Indebetouw, Remy
    Jerkstrand, Anders
    Ahola, Antero
    Burrows, David
    Challis, Peter
    Cigan, Phil
    Cikota, Aleksandar
    Kirshner, Robert P.
    van Loon, Jacco Th.
    Mattila, Seppo
    Ng, C. -Y.
    Park, Sangwook
    Spyromilio, Jason
    Woosley, Stan
    Baes, Maarten
    Bouchet, Patrice
    Chevalier, Roger
    Frank, Kari A.
    Gaensler, B. M.
    Gomez, Haley
    Janka, Hans-Thomas
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Marcaide, Jon
    Matsuura, Mikako
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Staveley-Smith, Lister
    Zanardo, Giovanna
    Gabler, Michael
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wheeler, J. Craig
    The 30 Year Search for the Compact Object in SN 1987A2018In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, no 2, article id 174Article in journal (Refereed)
    Abstract [en]

    Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.

  • 4. Alp, Dennis
    et al.
    Larsson, Josefin
    Maeda, Keiichi
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wongwathanarat, Annop
    Gabler, Michael
    Janka, Hans-Thomas
    Jerkstrand, Anders
    Heger, Alexander
    Menon, Athira
    X-Ray and Gamma-Ray Emission from Core-collapse Supernovae: Comparison of Three-dimensional Neutrino-driven Explosions with SN 1987A2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 882, no 1, article id 22Article in journal (Refereed)
    Abstract [en]

    During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit down-scattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the Ni-56 -> Co-56 -> Fe-56 chain. We use supernova (SN) models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of similar to 3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of SNe II-P and one model of a stripped-envelope SN IIb. The Type II-P models have observables similar to those of the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe.

  • 5.
    Bergdahl, Lars
    et al.
    Chalmers University of Technology.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Waves for design of wind-power plants in shallow seas2009In: Proceedings of the 20th International Conference on Port and Ocean Engineering under Arctic Conditions: June 9-12, 2009, Luleå, Sweden, 2009Conference paper (Refereed)
    Abstract [en]

    Usually there is little knowledge of long-term wave conditions at prospective sites for windpower plants, while the deep-water or open sea conditions may be more known and geographically less varying. However, most wind-energy plants are intended for water depths less than 20 m. A concept for assessing design waves at a near-shore site is to transform the offshore wave spectra to the target site by a model for spectral wave-energy transfer over the actual bottom topography. The inshore spectra can be used for linear statistics of extreme waves and design wave loads can be produced. In this context it is important to know the realism of used spectral forms.Based on 58 measured wave spectra at 6 m water depth at the near-shore wind farm Bockstigen in the Baltic the most realistic spectrum was found to be the TMA spectrum, which is a JONSWAP spectrum modified for shallow water. Some few examples are given.

  • 6. Berger, E.
    et al.
    Soderberg, A. M.
    Chevalier, R. A.
    Fransson, C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Foley, R. J.
    Leonard, D. C.
    Debes, J. H.
    Diamond-Stanic, A. M.
    Dupree, A. K.
    Ivans, I. I.
    Simmerer, J.
    Thompson, I. B.
    Tremonti, C. A.
    An Intermediate Luminosity Transient in NGC 300: The Eruption of a Dust-Enshrouded Massive Star2009In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 699, p. 1850-1865Article in journal (Refereed)
    Abstract [en]

    We present multi-epoch high-resolution optical spectroscopy, UV/radio/X-ray imaging, and archival Hubble and Spitzer observations of an intermediate luminosity optical transient recently discovered in the nearby galaxy NGC 300. We find that the transient (NGC 300 OT2008-1) has a peak absolute magnitude of M bol ≈ -11.8 mag, intermediate between novae and supernovae, and similar to the recent events M85 OT2006-1 and SN 2008S. Our high-resolution spectra, the first for this event, are dominated by intermediate velocity (~200-1000 km s-1) hydrogen Balmer lines and Ca II emission and absorption lines that point to a complex circumstellar environment, reminiscent of the yellow hypergiant IRC+10420. In particular, we detect asymmetric Ca II H&K absorption with a broad red wing extending to ~103 km s-1, indicative of gas inflow at high velocity (possibly the wind of a massive binary companion). The low luminosity, intermediate velocities, and overall similarity to a known eruptive star indicate that the event did not result in a complete disruption of the progenitor. We identify the progenitor in archival Spitzer observations, with deep upper limits from Hubble data. The spectral energy distribution points to a dust-enshrouded star with a luminosity of about 6 × 104 L sun, indicative of a ~10-20 M sun progenitor (or binary system). This conclusion is in good agreement with our interpretation of the outburst and circumstellar properties. The lack of significant extinction in the transient spectrum indicates that the dust surrounding the progenitor was cleared by the outburst. We thus predict that the progenitor should be eventually visible with Hubble if the transient event marks an evolutionary transition to a dust-free state, or with Spitzer if the event marks a cyclical process of dust formation.

  • 7.
    Bonath, Victoria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Edeskär, Tommy
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Lintzén, Nina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Fransson, Lennart
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Properties of ice from first-year ridges in the Barents Sea and Fram Strait2019In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 168, article id 102890Article in journal (Refereed)
    Abstract [en]

    First-year ice ridges are one of the main load scenarios that off-shore structures and vessels operating in ice-covered waters have to be designed for. For simulating such load scenarios, the knowledge gap on ice mechanical properties from the consolidated part of first-year ridges has to be filled. In total 410 small-scale uniaxial compression tests were conducted at different strain rates and ice temperatures on ice from the consolidated layer of 6 different first-year ridges in the sea around Svalbard. For the first time uniaxial tensile tests were performed on ice from first-year ridges using a new testing method. Ice strength was evaluated for different ice type, which are determined for each specimen based on a proposed ice classification system for ice from first-year ridges. 78% of all samples contained mixed ice with various compounds of brecciated columnar and granular ice. Ice strength of mixed ice showed isotropy, except for the samples containing mainly columnar ice crystals. For horizontal loading, mixed ice was stronger than columnar and granular ice. The residual strength of ductile ice depended on the strain rate. At 1.5% strain remained 70% of peak strength at 10−4 s−1 and 50% at 10−3 s−1. Ductile failure dominated for 75% of all mixed ice tests at 10−3 s−1 and − 10 °C. Ductile compressive strength was generally higher than brittle compressive strength for mixed ice. Brine volume was the main parameter influencing the tensile strength of the mixed ice which was between 0.14 MPa and 0.78 MPa measured at constant ice temperature of −10 °C.

  • 8.
    Bonath, Victoria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Isförhållanden inom Luleå hamnbassäng2013Report (Other academic)
    Abstract [sv]

    Issituationen i Luleå hamn vintern 2012/13 var normalsvår vilket innebar en ökad istillväxt motsvarade 150 cm ren is i områden som bröts kontinuerligt. Detta ska jämföras med det obrutna istäckets tjocklek som var ca 60 cm. Isen i rännan bestod av klotformade isblock (10 – 120 cm) omgivna av issörja. Under mars månad var isblockens storlek mätt vid vattenytan i genomsnitt 45 cm och andelen vatten eller finfördelad issörja var ca 30%. Analyser av isborrkärnor visar att isblocken hade en hållfasthet som ökade med antalet brytningar och var i paritet med det ostörda istäcket i början av mars. Blocken bestod då till 70% av finkrossad is eller frusen snösörja.Isproduktionen i området med bruten is tycks vara linjärt beroende av antalet negativa graddagar där tillväxttakten uppmättes till 0,235 cm per grad och dygn. En numerisk modell för beräkning av istillväxt föreslås där frysning av issörja vid ytan och under isblock ingår. Modellen stämmer bra överens med uppmätta värden från en ränna nära hamnen som bröts kontinuerligt två gånger i veckan. Mer fältstudier av isbildning och uppbrytning är önskvärd för att öka modellens tillförlitlighet under förhållanden som skiljer sig väsentligt från de som rådde i testrännan. Samtliga mätprotokoll från ismätningarna i rännan finns bifogade i rapporten.Tillgänglig statistik visar att antalet negativa graddagar efter isläggningen i Luleå hamn vid en svår isvinter är ca 1000. Våra mätningar tyder på att det under en sådan vinter bildas 2,4 m ren is om ett vändområde används kontinuerligt. Beräkningar med den numeriska modellen resulterade i en möjlig istjocklek på 3 m under en svår vinter om medeltemperaturen är 50% kallare än under den aktuella mätperioden 2012. I nuläget klarar hamnisbrytaren Viscaria att operera och vända fartyg i bruten is motsvarande 1,4 m. Om tjockare is bildas är det väsentligt att ett nytt vändområde med ostörd is kan tas i bruk. Under en svår isvinter krävs därför att minst tre åtskilda vändområden är tillgängliga i Luleå hamn.

  • 9.
    Bonath, Victoria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Patil, Aniket
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Sand, Björnar
    Laboratory testing of compressive and tensile strength on level ice and ridged ice from Svalbard region2013In: Proceedings of the 22nd International Conference on Port and Ocean Engineering under Arctic Conditions, 2013Conference paper (Refereed)
    Abstract [en]

    Compression and tensile strength properties are important input data for constitutive modelling. Still strength properties of ridged ice are not yet sufficiently investigated. During winter 2011 and 2012 field trips were performed to the Svalbard region with the aim to investigate structure and strength of pressure ridges. Core samples from different ridges and the surrounding level ice were taken and transported to the laboratory at Luleå University of Technology. Studies on thin sections of the ice samples under cross-polarized light delivered information about internal structure of the ice. Uniaxial compressive and tensile strength tests were performed with horizontal and vertical loading directions. The experimental procedure is explained in detail. Salinity and porosity were measured for each sample. In this paper the mechanical properties obtained from the testing are documented by consideration of crystal type, ice depth and total porosity.

  • 10.
    Bonath, Victoria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Petrich, Chris
    Northern Research Institute Narvik.
    Sand, Bjørnar
    Northern Research Institute Narvik.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Cwirzen, Andrzej
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Morphology, internal structure and formation of ice ridges in the sea around Svalbard2018In: Cold Regions Science and Technology, ISSN 0165-232X, E-ISSN 1872-7441, Vol. 155, p. 263-279Article in journal (Refereed)
    Abstract [en]

    The results from 3 years of comprehensive field investigations on first-year ice ridges in the Arctic are presented in this paper. The scopes of these investigations were to fill existing knowledge gaps on ice ridges, gain understanding on ridge characteristics and study internal properties of ice. The ability of developing reliable simulations and load predictions for ridge-structure interactions is the final principal purpose, but beyond the scope of this paper. The presented data comprise ridge geometry, ice block dimensions from ridge sails, ice structure in the ridge and values on the ridge porosity and the degree of consolidation. The total ridge thickness conformed to other ridges studied in the same regions. The consolidated layer thickness was on average 2–3 times the level ice thickness. Minimum 33% and in average 90% of the ridge keel area was consolidated. The distribution of ice block sizes and block shapes within a ridge appears to be predictable. A new approach for deriving a possible ridging scenario and ridge age is presented. Different steps of the ridge building process were identified, which are in good agreement with earlier simulated ridging events. After formation of very thin lead ice between two floes deformation occurs through rafting and ridging until closure of the lead. Subsequently the adjacent level ice floe fractures proceeding ridge formation until ridging forces exceed driving forces. A time span of 10 days could be assessed for a possible ridge formation date, estimating the ridge age of the studied ridge located east of Edgeøya at 78° N to be 7 to 8 weeks.

  • 11.
    Casselgren, Johan
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Engström, Niclas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Rosendahl, Sara
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Investigation of ice surface change during vehicle testing2014In: International Journal of Vehicle Systems Modelling and Testing, ISSN 1745-6436, E-ISSN 1745-6444, Vol. 9, no 2, p. 137-150Article in journal (Refereed)
    Abstract [en]

    Today, there are a lot of vehicles and tyre testing carried out on lake ice surfaces. Thus, it is important to have knowledge about parameters that affect roadgrip. The thesis within this paper is that the liquid like layer which appears due to increasing temperature can be reduced by manipulating the ice roughness. This in turn should decrease the temperature dependence of the roadgrip in temperatures around 0°C. In order to investigate this, measurements of temperature, surface roughness and hardness and roadgrip were performed on three outdoor ice surfaces using an IR thermometer, an optical sensor with three IR-diodes, a steel ball drop indentation test and an RT3 curve, respectively. Additional ice roughness measurements were also made on two tempered ice surfaces in an ice hall. Results show a clear connection between ice temperature and roadgrip, unfortunately the created ice roughness was too small to influence the change in roadgrip

  • 12.
    Cederwall, Krister
    et al.
    Luleå tekniska universitet.
    Degerman, Tryggve
    Luleå tekniska universitet.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Ispåverkan på plana låglutande papptäckta tak1984Report (Other academic)
  • 13. Cederwall, Krister
    et al.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Cracking a roof felt caused by an ice-cover1989In: POAC '89: 10th International conference on port and ocean engineering under arctic conditions / [ed] Kenneth B.E. Axelsson; Lennart Å. Fransson, Luleå: Luleå tekniska universitet, 1989, Vol. 2, p. 796-807Conference paper (Other academic)
  • 14. Chakraborti, Sayan
    et al.
    Soderberg, Alicia
    Chomiuk, Laura
    Kamble, Atish
    Yadav, Naveen
    Ray, Alak
    Hurley, Kevin
    Margutti, Raffaella
    Milisavljevic, Dan
    Bietenholz, Michael
    Brunthaler, Andreas
    Pignata, Giuliano
    Pian, Elena
    Mazzali, Paolo
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Bartel, Norbert
    Hamuy, Mario
    Levesque, Emily
    MacFadyen, Andrew
    Dittmann, Jason
    Krauss, Miriam
    Briggs, M. S.
    Connaughton, V.
    Yamaoka, K.
    Takahashi, T.
    Ohno, M.
    Fukazawa, Y.
    Tashiro, M.
    Terada, Y.
    Murakami, T.
    Goldsten, J.
    Barthelmy, S.
    Gehrels, N.
    Cummings, J.
    Krimm, H.
    Palmer, D.
    Golenetskii, S.
    Aptekar, R.
    Frederiks, D.
    Svinkin, D.
    Cline, T.
    Mitrofanov, I. G.
    Golovin, D.
    Litvak, M. L.
    Sanin, A. B.
    Boynton, W.
    Fellows, C.
    Harshman, K.
    Enos, H.
    von Kienlin, A.
    Rau, A.
    Zhang, X.
    Savchenko, V.
    A MISSING-LINK IN THE SUPERNOVA-GRB CONNECTION: THE CASE OF SN 2012ap2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 805, no 2, article id 187Article in journal (Refereed)
    Abstract [en]

    Gamma-ray bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly, usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However, supernovae with heavy ejecta can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for a few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. However, the ejecta from SN 2009bb was baryon loaded and in nearly free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than one-sixth of the fluence from GRB 980425. This shows for the first time that central engines in SNe Ic, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

  • 15. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Irwin, Christopher M.
    Soderberg, Alicia M.
    Chakraborti, Sayan
    Immler, Stefan
    Radio and x ray observations of sn 2006jd: another strongly interacting type iin supernova2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 755, no 2, p. 110-Article in journal (Refereed)
    Abstract [en]

    We report four years of radio and X-ray monitoring of the Type IIn supernova SN 2006jd at radio wavelengths with the Very Large Array, Giant Metrewave Radio Telescope, and Expanded Very Large Array; at X-ray wavelengths with Chandra, XMM-Newton, and Swift-XRT. We assume that the radio and X-ray emitting particles are produced by shock interaction with a dense circumstellar medium. The radio emission shows an initial rise that can be attributed to free-free absorption by cool gas mixed into the nonthermal emitting region; external free-free absorption is disfavored because of the shape of the rising light curves and the low gas column density inferred along the line of sight to the emission region. The X-ray luminosity implies a preshock circumstellar density similar to 10(6) cm(-3) at a radius r similar to 2 x 10(16) cm, but the column density inferred from the photoabsorption of X-rays along the line of sight suggests a significantly lower density. The implication may be an asymmetry in the interaction. The X-ray spectrum shows Fe line emission at 6.9 keV that is stronger than is expected for the conditions in the X-ray emitting gas. We suggest that cool gas mixed into the hot gas plays a role in the line emission. Our radio and X-ray data both suggest the density profile is flatter than r(-2) because of the slow evolution of the unabsorbed emission.

  • 16. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Soderberg, Alicia M.
    X-RAY AND RADIO EMISSION FROM TYPE IIn SUPERNOVA SN 2010jl2015In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 810, no 1, article id 32Article in journal (Refereed)
    Abstract [en]

    We present all X-ray and radio observations of the Type IIn supernova SN 2010jl. The X-ray observations cover a period up to day 1500 with Chandra, XMM-Newton, NuSTAR, and Swift-X-ray Telescope (XRT). The Chandra observations after 2012 June, the XMM-Newton observation in 2013 November, and most of the Swift-XRT observations until 2014 December are presented for the first time. All the spectra can be fitted by an absorbed hot thermal model except for Chandra spectra on 2011 October and 2012 June when an additional component is needed. Although the origin of this component is uncertain, it is spatially coincident with the supernova and occurs when there are changes to the supernova spectrum in the energy range close to that of the extra component, indicating that the emission is related to the supernova. The X-ray light curve shows an initial plateau followed by a steep drop starting at day similar to 300. We attribute the drop to a decrease in the circumstellar density. The column density to the X-ray emission drops rapidly with time, showing that the absorption is in the vicinity of the supernova. We also present Very Large Array radio observations of SN 2010jl. Radio emission was detected from SN 2010jl from day 570 onwards. The radio light curves and spectra suggest that the radio luminosity was close to its maximum at the first detection. The velocity of the shocked ejecta derived assuming synchrotron self-absorption is much less than that estimated from the optical and X-ray observations, suggesting that free-free absorption dominates.

  • 17. Chandra, Poonam
    et al.
    Chevalier, Roger A.
    Irwin, Christopher M.
    Chugai, Nikolai
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Söderberg, Alicia M.
    STRONG EVOLUTION OF X-RAY ABSORPTION IN THE TYPE IIn SUPERNOVA SN 2010jl2012In: ASTROPHYSICAL JOURNAL LETTERS, ISSN 2041-8205, Vol. 750, no 1, p. L2-Article in journal (Refereed)
    Abstract [en]

    We report two epochs of Chandra-ACIS X-ray imaging spectroscopy of the nearby bright Type IIn supernova SN 2010jl, taken around two months and then a year after the explosion. The majority of the X-ray emission in both spectra is characterized by a high temperature (greater than or similar to 10 keV) and is likely to be from the forward shocked region resulting from circumstellar interaction. The absorption column density in the first spectrum is high (similar to 10(24) cm(-2)), more than three orders of magnitude higher than the Galactic absorption column, and we attribute it to absorption by circumstellar matter. In the second epoch observation, the column density has decreased by a factor of three, as expected for shock propagation in the circumstellar medium. The unabsorbed 0.2-10 keV luminosity at both epochs is similar to 7 x 10(41) erg s(-1). The 6.4 keV Fe line clearly present in the first spectrum is not detected in the second spectrum. The strength of the fluorescent line is roughly that expected for the column density of circumstellar gas, provided the Fe is not highly ionized. There is also evidence for an absorbed power-law component in both spectra, which we attribute to a background ultraluminous X-ray source.

  • 18. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Circumstellar Emission from Type Ib and Ic Supernovae2006In: The Astrophysical Journal, ISSN 0004-637X, Vol. 651, no 1, p. 381-391Article in journal (Refereed)
    Abstract [sv]

    The presumed Wolf-Rayet star progenitors of Type Ib/c supernovae have fast, low-density winds, and the shock waves generated by the supernova interaction with the wind are not expected to be radiative at typical times of observation. The injected energy spectrum of radio-emitting electrons typically has an observed index p=3, which is suggestive of acceleration in cosmic-ray-dominated shocks. The early, absorbed part of the radio light curves can be attributed to synchrotron self-absorption, which leads to constraints on the magnetic field in the emitting region and on the circumstellar density. The range of circumstellar densities inferred from the radio emission is somewhat broader than that for Galactic Wolf-Rayet stars, if similar efficiencies of synchrotron emission are assumed in the extragalactic supernovae. For the observed and expected ranges of circumstellar densities to roughly overlap, a high efficiency of magnetic field production in the shocked region is required (ɛB~0.1). For the expected densities around a Wolf-Rayet star, a nonthermal mechanism is generally required to explain the observed X-ray luminosities of Type Ib/c supernovae. Inverse Compton emission is a candidate for the emission, if the observations are near optical maximum. In other cases we suggest that the mechanism is X-ray synchrotron emission in a situation in which the shock wave is cosmic-ray-dominated so that the electron energy spectrum flattens at high energy. More comprehensive X-ray observations of a Type Ib/c supernova are needed to determine whether this suggestion is correct.

  • 19. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Shock Breakout Emission from a Type Ib/c Supernova: XRT 080109/SN 2008D2008In: The Astrophysical Journal, Vol. 683, no 2, p. L135-L138Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    The X-ray transient 080109, associated with SN 2008D, can be attributed to the shock breakout emission from a normal Type Ib/c supernova. If the observed emission is interpreted as thermal emission, the temperature and radiated energy are close to expectations, considering that scattering dominates absorption processes so that spectrum formation occurs deep within the photosphere. The X-ray emission observed at ~10 days is attributed to inverse Compton scattering of photospheric photons with relativistic electrons produced in the interaction of the supernova with the progenitor wind. A simple model for the optical/ultraviolet emission from shock breakout is developed and applied to SN 1987A, SN 1999ex, SN 2008D, and SN 2006aj, all of which have optical emission observed at t~1 day. The emission from the first three can plausibly be attributed to shock breakout emission. The photospheric temperature is most sensitive to the radius of the progenitor star core and the radii in these cases are in line with expectations from stellar evolution. The early optical/ultraviolet observations of SN 2006aj cannot be accommodated by a nonrelativistic shock breakout model in a straightforward way.

  • 20. Chevalier, Roger
    et al.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Nymark, Tanja
    Stockholm University, Faculty of Science, Department of Astronomy.
    Radio and X-Ray Emission as Probes of Type IIP Supernovae and Red Supergiant Mass Loss2006In: The Astrophysical Journal, ISSN 0004-637X, Vol. 641, no 2, p. 1029-1038Article in journal (Refereed)
    Abstract [en]

    Type IIP (plateau) supernovae are thought to come from stars with initial mass ~8-25 Msolar that end their lives as red supergiants. The expected stellar endpoints can be found from evolutionary calculations, and the corresponding mass-loss properties at these points can be estimated from typical values for Galactic stars. The mass-loss densities of observed supernovae can be estimated from observations of the thermal X-ray and radio synchrotron emission that result from the interaction of the supernova with the surrounding wind. Type IIP supernovae are expected to have energy-conserving interaction during typical times of observation. Because Type IIP supernovae have an extended period of high optical luminosity, Compton cooling could affect the radio-emitting electrons, giving rise to a relatively flat radio light curve in the optically thin regime. Alternatively, a high efficiency of magnetic field production results in synchrotron cooling of the radio-emitting electrons. Both the X-ray and radio luminosities are sensitive to the mass loss and initial masses of the progenitor stars, although the turn-on of radio emission is probably the best estimator of circumstellar density. Both the mass-loss density and the variation of density with stellar mass are consistent with expectations for the progenitor stars deduced from direct observations of recent supernovae. Current observations are consistent with mass being the only parameter; observations of supernovae in metal-poor regions could show how the mass loss depends on metallicity.

  • 21. Chomiuk, Laura
    et al.
    Soderberg, Alicia M.
    Chevalier, Roger A.
    Bruzewski, Seth
    Foley, Ryan J.
    Parrent, Jerod
    Strader, Jay
    Badenes, Carles
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kamble, Atish
    Margutti, Raffaella
    Rupen, Michael P.
    Simon, Joshua D.
    A DEEP SEARCH FOR PROMPT RADIO EMISSION FROM THERMONUCLEAR SUPERNOVAE WITH THE VERY LARGE ARRAY2016In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 821, no 2, article id 119Article in journal (Refereed)
    Abstract [en]

    Searches for circumstellar material around Type Ia supernovae (SNe Ia) are some of the most powerful tests of the nature of SN Ia progenitors, and radio observations provide a particularly sensitive probe of this material. Here, we report radio observations for SNe. Ia and their lower-luminosity thermonuclear cousins. We present the largest, most sensitive, and spectroscopically diverse study of prompt (Delta t less than or similar to 1 years) radio observations of 85 thermonuclear SNe, including 25 obtained by our team with the unprecedented depth of the Karl G. Jansky Very Large Array. With these observations, SN 2012cg joins SN 2011fe and SN 2014J as an SN. Ia with remarkably deep radio limits and excellent temporal coverage (six epochs, spanning 5-216 days after explosion, implying <(M)over dot>/v(w) less than or similar to 5 x 10(-9) M-circle dot yr(-1)/100 km s(-1), assuming epsilon(B) = 0.1 and epsilon(e) = 0.1). All observations yield non-detections, placing strong constraints on the presence of circumstellar material. We present analytical models for the temporal and spectral evolution of prompt radio emission from thermonuclear SNe as expected from interaction with either wind-stratified or uniform density media. These models allow us to constrain the progenitor mass loss rates, with limits in the range of <(M)over dot> less than or similar to 10(-9) - 10(-4) M-circle dot yr(-1), assuming a wind velocity of v(w) = 100 km s(-1). We compare our radio constraints with measurements of Galactic symbiotic binaries to conclude that less than or similar to 10% of thermonuclear SNe have red giant companions.

  • 22. Chomiuk, Laura
    et al.
    Söderberg, Alicia M.
    Moe, Maxwell
    Chevalier, Roger A.
    Rupen, Michael P.
    Badenes, Carles
    Margutti, Raffaella
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fong, Wen-fai
    Dittmann, Jason A.
    EVLA OBSERVATIONS CONSTRAIN THE ENVIRONMENT AND PROGENITOR SYSTEM OF Type Ia SUPERNOVA 2011fe2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 750, no 2, p. 164-Article in journal (Refereed)
    Abstract [en]

    We report unique Expanded Very Large Array observations of SN 2011fe representing the most sensitive radio study of a Type Ia supernova to date. Our data place direct constraints on the density of the surrounding medium at radii similar to 10(15)-10(16) cm, implying an upper limit on the mass loss rate from the progenitor system of (M) over dot less than or similar to 6x10(-10) M-circle dot yr(-1) (assuming a wind speed of 100 km s(-1)) or expansion into a uniform medium with density n(CSM) less than or similar to 6 cm(-3). Drawing from the observed properties of non-conservative mass transfer among accreting white dwarfs, we use these limits on the density of the immediate environs to exclude a phase space of possible progenitor systems for SN 2011fe. We rule out a symbiotic progenitor system and also a system characterized by high accretion rate onto the white dwarf that is expected to give rise to optically thick accretion winds. Assuming that a small fraction, 1%, of the mass accreted is lost from the progenitor system, we also eliminate much of the potential progenitor parameter space for white dwarfs hosting recurrent novae or undergoing stable nuclear burning. Therefore, we rule out much of the parameter space associated with popular single degenerate progenitor models for SN 2011fe, leaving a limited phase space largely inhabited by some double degenerate systems, as well as exotic single degenerates with a sufficient time delay between mass accretion and SN explosion.

  • 23. Cigan, Phil
    et al.
    Matsuura, Mikako
    Gomez, Haley L.
    Indebetouw, Remy
    Abellán, Fran
    Gabler, Michael
    Richards, Anita
    Alp, Dennis
    Davis, Timothy A.
    Janka, Hans-Thomas
    Spyromilio, Jason
    Barlow, M. J.
    Burrows, David
    Dwek, Eli
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gaensler, Bryan
    Larsson, Josefin
    Bouchet, P.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Marcaide, J. M.
    Ng, C. -Y.
    Park, Sangwook
    Roche, Pat
    van Loon, Jacco Th.
    Wheeler, J. C.
    Zanardo, Giovanna
    High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta2019In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 886, no 1, article id 51Article in journal (Refereed)
    Abstract [en]

    We present high angular resolution (similar to 80 mas) ALMA continuum images of the SN.1987A system, together with CO J = 2 -> 1, J = 6 -> 5, and SiO J = 5 -> 4 to J = 7 -> 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in H alpha images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J = 6 -> 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J = 6 -> 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J = 2 -> 1 and SiO J = 5 -> 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared-millimeter spectral energy distribution give ejecta dust temperatures of 18-23 K. We revise the ejecta dust mass to M-dust = 0.2-0.4 M-circle dot for carbon or silicate grains, or a maximum of <0.7 M-circle dot for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.

  • 24. Clocchiatti, Alejandro
    et al.
    Wheeler, J. Craig
    Kirshner, Robert P.
    Branch, David
    Challis, Peter
    Chevalier, Roger A.
    Filippenko, Alexei V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Garnavich, Peter
    Leibundgut, Bruno
    Panagia, Nino
    Phillips, Mark M.
    Suntzeff, Nicholas B.
    Hoeflich, Peter A.
    Gallardo, Jose
    Late-time HST photometry of SN1994I: Hints of positron annihilation energy deposition2008In: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 120, no 865, p. 290-300Article in journal (Refereed)
    Abstract [en]

    We present multicolor Hubble Space Telescope ( HST) WFPC2 broadband observations of the Type Ic SN 1994I obtained similar to 280 d after maximum light. We measure the brightness of the SN and, relying on the detailed spectroscopic database of SN 1994I, we transform the ground-based photometry obtained at early times to the HST photometric system, deriving light curves for the WFPC2 F439W, F555W, F675W, and F814W passbands that extend from 7 days before to 280 days after maximum. We use the multicolor photometry to build a quasi-bolometric light curve of SN 1994I, and compare it with similarly constructed light curves of other supernovae. In doing so, we propose and test a scaling in energy and time that allows for a more meaningful comparison of the exponential tails of different events. Through comparison with models, we find that the late-time light curve of SN 1994I is consistent with that of spherically symmetric ejecta in homologous expansion, for which the ability to trap the gamma-rays produced by the radioactive decay of Co-56 diminishes roughly as the inverse of time squared. We also find that by the time of the HST photometry, the light curve was significantly energized by the annihilation of positrons.

  • 25.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dickinson, Hugh
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Design concepts for the Cherenkov Telescope Array CTA: an advanced facility for ground-based high-energy gamma-ray astronomy2011In: Experimental astronomy (Print), ISSN 0922-6435, E-ISSN 1572-9508, Vol. 32, no 3, p. 193-316Article in journal (Refereed)
    Abstract [en]

    Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.

  • 26.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Dickinson, Hugh J.
    Stockholm University, Faculty of Science, Department of Physics.
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. University of Geneva, Switzerland.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Ripken, Joachim
    Stockholm University, Faculty of Science, Department of Physics.
    Introducing the CTA concept2013In: Astroparticle physics, ISSN 0927-6505, E-ISSN 1873-2852, Vol. 43, p. 3-18Article in journal (Refereed)
    Abstract [en]

    The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project.

  • 27. Dahlen, Tomas
    et al.
    Melinder, J.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mencia Trinchant, L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Mattila, S.
    Ostlin, G.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Fransson, C.
    Stockholm University, Faculty of Science, Department of Astronomy.
    The Stockholm Vimos Supernova Survey (SVISS) - First Results From An Intermediate Redshift Sn Survey2009Conference paper (Refereed)
    Abstract [en]

    The aim of the Stockholm VIMOS Supernova Survey is to find and characterize supernovae in the redshift range 0.1 to 1.2 and to derive accurate supernova rate densities for this redshift range. A preliminary analysis show that we have 14 prime SN candidates and an additional 23 less secure detections in one of our search fields. A sample of R+I light curves for the prime candidates will be presented. We will also show some results from testing of our supernova search pipeline and our supernova typing method.

  • 28. De, K.
    et al.
    Kasliwal, M. M.
    Ofek, E. O.
    Moriya, T. J.
    Burke, J.
    Cao, Y.
    Cenko, S. B.
    Doran, G. B.
    Duggan, G. E.
    Fender, R. P.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Gal-Yam, A.
    Horesh, A.
    Kulkarni, S. R.
    Laher, R. R.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Manulis, I.
    Masci, F.
    Mazzali, P. A.
    Nugent, P. E.
    Perley, D. A.
    Petrushevska, Tanja
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). University of Nova Gorica, Slovenia.
    Piro, A. L.
    Rumsey, C.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sullivan, M.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    A hot and fast ultra-stripped supernova that likely formed a compact neutron star binary2018In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 362, no 6411, p. 201-206Article in journal (Refereed)
    Abstract [en]

    Compact neutron star binary systems are produced from binary massive stars through stellar evolution involving up to two supernova explosions. The final stages in the formation of these systems have not been directly observed. We report the discovery of iPTF 14gqr (SN 2014ft), a type Ic supernova with a fast-evolving light curve indicating an extremely low ejecta mass (approximate to 0.2 solar masses) and low kinetic energy (approximate to 2 x 10(50) ergs). Early photometry and spectroscopy reveal evidence of shock cooling of an extended helium-rich envelope, likely ejected in an intense pre-explosion mass-loss episode of the progenitor. Taken together, we interpret iPTF 14gqr as evidence for ultra-stripped supernovae that form neutron stars in compact binary systems.

  • 29.
    Dempsey, John P.
    et al.
    Clarkson University, Potsdam, NY.
    Jochmann, Peter
    Hamburg Ship Model Basin.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Mu, Z.
    MMI Engineering, Houston, TX..
    Weiss, Jerome
    CNRS, LGGE, Saint-Martin d'Hères.
    Palmer, A.C.
    National University of Singapore.
    Cleavage fracture of warm brackish ice2013In: Proceedings of the International Conference on Port and Ocean Engineering under Arctic Conditions: June 9-13, 2013 Espoo, Finland, 2013Conference paper (Refereed)
    Abstract [en]

    Two sets of cleavage (cracking parallel to the ice surface) fracture toughness tests were conducted at the Hamburg Ship Model Basin (HSVA) on brackish ice harvested from two separate locations in the Gulf of Bothnia. The ice was split using a pin-loaded compact tension geometry. The fracture tests were accompanied by tensile and compressive tests. This paper discusses the experiments and the results.

  • 30.
    Dhawan, Suhail
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, J.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kulkarni, R.
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Miller, A. A.
    iPTF16abc and the population of Type Ia supernovae: comparing the photospheric, transitional, and nebular phases2018In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 480, no 2, p. 1445-1456Article in journal (Refereed)
    Abstract [en]

    Key information about the progenitor system and the explosion mechanism of Type la supernovae (SNe Ia) can be obtained from early observations, within a few days from explosion. iPTF16abc was discovered as a young SN la with excellent early time data. Here, we present photometry and spectroscopy of the SN in the nebular phase. A comparison of the early time data with a sample of SNe la shows distinct features, differing from normal SNe la at early phases but similar to normal SNe Ia at a few weeks after maximum light (i.e. the transitional phase) and well into the nebular phase. The transparency time-scales (t(0)) for this sample of SNe Ia range between similar to 25 and 41 d indicating a diversity in the ejecta masses. t(0) also weakly correlates with the peak bolometric luminosity, consistent with the interpretation that SNe with higher ejecta masses would produce more Ni-56. Comparing the to and the maximum luminosity, L-max distribution of a sample of SNe Ia to predictions from a wide range of explosion models we find an indication that the sub-Chandrasekhar mass models span the range of observed values. However, the bright end of the distribution can be better explained by Chandrasekhar mass delayed detonation models, hinting at multiple progenitor channels to explain the observed bolometric properties of SNe Ia. iPTF16abc appears to be consistent with the predictions from the M-ch models.

  • 31.
    Domaschuk, L.
    et al.
    University of Manitoba, Winnipeg.
    Shields, D.H.
    University of Manitoba, Winnipeg.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Reactive soil pressures along pile in frozen sand1991In: Journal of cold regions engineering, ISSN 0887-381X, E-ISSN 1943-5495, Vol. 5, no 4, p. 174-194Article in journal (Refereed)
    Abstract [en]

    A multistage, lateral, pile-load creep test is carried out in a frozen sand maintained at -3° C. The pile is a tubular pipe, 150 mm square and 1,800 mm long. A series of plate load cells is mounted along the primary bearing face of the pile. Application of lateral loads of 35, 65, and 115 kN result in attenuating creep, whereas a lateral load of 145 kN leads to accelerating creep. The immediate components of pile displacement increase approximately linearly with applied load, while the creep components increase exponentially. Generally, the soil reaction forces near the ground surface decrease as the result of pile creep, and those further down the pile increase. Moduli of horizontal subgrade reaction computed on the basis of the measured soil reaction forces and the pile displacement are found to vary with applied pressure and creep. Magnitudes based on immediate displacements range from 1 to 7.5 GN/m3, while those based on total displacements range from 0.3 to 2 GN/m3.

  • 32.
    Domaschuk, Len
    et al.
    University of Manitoba, Winnipeg.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Shields, Don H.
    University of Manitoba, Winnipeg.
    Interaction between a laterally loaded pile and frozen soil1988In: Permafrost: Fifth International Conference : proceedings : August 2-5, 1988 / [ed] Kaare Senneset, Trondheim: Tapir Academic Press , 1988, Vol. 2, p. 1060-1065Conference paper (Refereed)
  • 33.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fransson, Lennart
    Täljsten, Björn
    Infrastructure in NW Russia: potential development: a pre-feasibility study with special reference to winter transportation, concrete structures and timber structures2000Report (Other academic)
  • 34.
    Elfgren, Lennart
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Fire Engineering.
    Täljsten, Björn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering. Skanska Teknik AB.
    Infrastructure in NW Russia - Potential development: A Pre-feasibility Study with Special Reference to Winter Transportation, Concrete Structures, and Timber Structures 2000Report (Other academic)
    Abstract [en]

    In co-operation with a Finnish Group of researchers a pre-feasibility study was undertaken regarding potential development of the Infrastructure in NW Russia. Special emphasis was given: Winter Transportation and Reinforcement of Load Bearing Ice Covers; Concrete Construction and Strengthening of Concrete Structures; Timber Construction and Mechanical Wood Industry Development; and Energy Conservation and Industrial Energy Development.

    Based on the study three Russian-Swedish co-operation projects have started:

    - Load Bearing Ice Covers (Literature Survey)

    - Forces caused by Ice Crushing against Off-Shore Structures (EC funded Research Project)

    - Strengthening of a Bridge. Co-operation Stabilator/Skanska - Arkhangelsk Road

  • 35.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Direct low lateral slip roadgrip measurement compared with surface reflection of three laser beams2011Conference paper (Other academic)
  • 36.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Discrepancies between longitudinal high slip and lateral low slip friction measurements on prepared ice surfaces: Paper and poster2009In: Compendium of papers DVD, TRB 88th annual meeting: January 11 - 15, 2009, Washington, D.C, Washington, DC: TRB , 2009, p. 1-13Conference paper (Refereed)
    Abstract [en]

    The Swedish road administration requested that an independent organization facilitate friction tests with several types of friction measuring devices. These tests were done on the following three surfaces: macro rough and micro smooth ice, macro- and micro smooth ice and macroand micro rough ice. The objective was to evaluate lateral low slip measuring devices against traditional longitudinal high slip devices. This was done by evaluating how they measure road grip, i.e. friction differences between road surfaces and the measuring tire. Tests were performed on Lake Kakel near Arjeplog, northern Sweden on March 18th, 2008. Weather conditions were stable with ice temperatures between -4°C (24.8°F) and -3°C (26.6°F). Tests showed that changes on the ice surfaces were readily detected with all four of the lateral low slip friction measurement devices and the two longitudinal high slip devices. Friction resolutions were higher with low lateral slip devices compared to high longitudinal slip devices. The tires on the devices were of different types and are the main reason for the difference in friction resolution. One major difference was detected; the lateral low slip method measured higher friction between its regular winter tire and the macro rough, micro smooth surfacecompared to the friction on the macro- and micro rough ice. Longitudinal high slip devices measured higher friction between its industrial friction tire and macro- and micro rough ice. Capacity to measure friction in curves was only displayed by the high longitudinal slip devices.

  • 37.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Stop distances for ten studless winter tires2009Report (Other academic)
    Abstract [sv]

    Denna rapport innehåller stoppsträckor för tio omgångar dubbfria vinterdäck. Arbetets huvudmål är att kunna skapa en grund för vinterdäcksklassificering. Så småning om skall traffikanter kunna få relevant information om olika däckens förmåga att skapa tillräckligt väggrepp på farliga vinterväglag. Vägverket ser ett ökat behov av kunskap då dubbdäcksanvändandet kommer att minskas i framtiden.

  • 38.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Nybacka, Mikael
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Road grip test in Arjeplog2008Report (Other academic)
    Abstract [en]

    The Swedish road administration sees a need to improve the road grip estimation capacity for the Swedish road system. The challenge is to find methods to measure road grip fast and reliable. There where six different system types at the tests in Arjeplog, three continuous, two system measuring road grip through deceleration and one system based on GPS and accelerometers. Two system types used air craft runway tires. The other systems used either studded winter tires or friction winter tires. Test runs where performed and road grip where recorded for three different surface types, old system 2000 ice, polished ice and new system 2000 ice. Weather data was collected during the three days. It is clear that all systems can detect changes in road grip. It is clear that continuous systems hold an information advantage over the sequence oriented systems. For measurements of road grip on winter roads, we recommend that rubber compounds adapted for cold conditions are used, as the resolution of the road grip measurement where better. In extreme condition like on polished ice, studded winter tires increase the road grip significantly.

  • 39.
    Engström, Niclas
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Andrén, Henrik
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Fransson, Lennart
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Structural and Construction Engineering.
    Direct low lateral slip roadgrip measurement compared with surface reflection of three laser beams2010Conference paper (Refereed)
    Abstract [en]

    Road grip on roads depend on many factors and different techniques are available to estimate available road grip. To ensure that entrepreneurs have successfully restored the road grip to an acceptable level both entrepreneurs and road keepers need tools to evaluate present road grip. Information about road grip can also be utilized directly in a vehicle if available, for systems such as ABS, traction control, etc. To evaluate a non-contact method based on three laser beams with different frequency this equipment was mounted on a car equipped with a fifth wheel behind the car. The wheel is angled about 1.5 degrees compared with the centreline of travel. A force sensor in the hub measures forces acting on a standard winter tire also mounted to the hub, this is considered to be one measurement of road grip. The main reason is to see how well one can estimate road grip with a low cost non contact device made with Laser beams in combination with a photodiode.

  • 40.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, A.
    Kozma, Cecilia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Kromer, M.
    Spricer, Kristoffer
    Stockholm University, Faculty of Science, Department of Mathematics.
    Monte-Carlo methods for NLTE spectral synthesis of supernovae2018In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, article id A156Article in journal (Refereed)
    Abstract [en]

    We present JEKYLL, a new code for modelling of supernova (SN) spectra and lightcurves based on Monte-Carlo (MC) techniques for the radiative transfer. The code assumes spherical symmetry, homologous expansion and steady state for the matter, but is otherwise capable of solving the time-dependent radiative transfer problem in non-local-thermodynamic-equilibrium (NLTE). The method used was introduced in a series of papers by Lucy, but the full time-dependent NLTE capabilities of it have never been tested. Here, we have extended the method to include non-thermal excitation and ionization as well as charge-transfer and two-photon processes. Based on earlier work, the non-thermal rates are calculated by solving the Spencer-Fano equation. Using a method previously developed for the SUMO code, macroscopic mixing of the material is taken into account in a statistical sense. To save computational power a diffusion solver is used in the inner region, where the radiation field may be assumed to be thermalized. In addition, a statistical Markov-chain model is used to sample the emission frequency more efficiently, and we introduce a method to control the sampling of the radiation field, which is used to reduce the noise in the radiation field estimators. Except for a description of JEKYLL, we provide comparisons with the ARTIS, SUMO and CMFGEN codes, which show good agreement in the calculated spectra as well as the state of the gas. In particular, the comparison with CMFGEN, which is similar in terms of physics but uses a different technique, shows that the Lucy method does indeed converge in the time-dependent NLTE case. Finally, as an example of the time-dependent NLTE capabilities of JEKYLL, we present a model of a Type IIb SN, taken from a set of models presented and discussed in detail in an accompanying paper. Based on this model we investigate the effects of NLTE, in particular those arising from non-thermal excitation and ionization, and find strong effects even on the bolometric lightcurve. This highlights the need for full NLTE calculations when simulating the spectra and lightcurves of SNe.

  • 41.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, A.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Elias-Rosa, N.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Pastorello, A.
    Kotak, R.
    Taubenberger, S.
    Tomasella, L.
    Valenti, S.
    Benetti, S.
    Helou, G.
    Kasliwal, M. M.
    Maund, J.
    Smartt, S. J.
    Spyromilio, J.
    The Type IIb SN 2011dh: Two years of observations and modelling of the lightcurves2015In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 580, article id A142Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared (NIR) photometry and spectroscopy as well as modelling of the lightcurves of the Type IIb supernova (SN) 2011dh. Our extensive dataset, for which we present the observations obtained after day 100, spans two years, and complemented with Spitzer mid-infrared (MIR) data, we use it to build an optical-to-MIR bolometric lightcurve between days 3 and 732. To model the bolometric lightcurve before day 400 we use a grid of hydrodynamical SN models, which allows us to determine the errors in the derived quantities, and a bolometric correction determined with steady-state non-local thermodynamic equilibrium (NLTE) modelling. Using this method we find a helium core mass of 3.1+0.7-0.4 M for SN 2011dh, consistent within error bars with previous results obtained using the bolometric lightcurve before day 80. We compute bolometric and broad-band lightcurves between days 100 and 500 from spectral steady-state NLTE models, presented and discussed in a companion paper. The preferred 12 M (initial mass) model, previously found to agree well with the observed spectra, shows a good overall agreement with the observed lightcurves, although some discrepancies exist. Time-dependent NLTE modelling shows that after day ~600 a steady-state assumption is no longer valid. The radioactive energy deposition in this phase is likely dominated by the positrons emitted in the decay of 56Co, but seems insufficient to reproduce the lightcurves, and what energy source is dominating the emitted flux is unclear. We find an excess in the K and the MIR bands developing between days 100 and 250, during which an increase in the optical decline rate is also observed. A local origin of the excess is suggested by the depth of the He I 20 581 Å absorption. Steady-state NLTE models with a modest dust opacity in the core (τ = 0.44), turned on during this period, reproduce the observed behaviour, but an additional excess in the Spitzer 4.5 μm band remains. Carbon-monoxide (CO) first-overtone band emission is detected at day 206, and possibly at day 89, and assuming the additional excess to bedominated by CO fundamental band emission, we find fundamental to first-overtone band ratios considerably higher than observed in SN 1987A. The profiles of the [O I] 6300 Å and Mg I] 4571 Å lines show a remarkable similarity, suggesting that these lines originate from a common nuclear burning zone (O/Ne/Mg), and using small scale fluctuations in the line profiles we estimate a filling factor of ≲0.07 for the emitting material. This paper concludes our extensive observational and modelling work on SN 2011dh. The results from hydrodynamical modelling, steady-state NLTE modelling, and stellar evolutionary progenitor analysis are all consistent, and suggest an initial mass of ~12 M for the progenitor.

  • 42.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fraser, M.
    Pastorello, A.
    Taubenberger, S.
    Elias-Rosa, N.
    Bersten, M.
    Jerkstrand, A.
    Benetti, S.
    Botticella, M. T.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Harutyunyan, A.
    Kotak, R.
    Smartt, S.
    Valenti, S.
    Bufano, F.
    Cappellaro, E.
    Fiaschi, M.
    Howell, A.
    Kankare, E.
    Magill, L.
    Mattila, S.
    Maund, J.
    Naves, R.
    Ochner, P.
    Ruiz, J.
    Smith, K.
    Tomasella, L.
    Turatto, M.
    Optical and near-infrared observations of SN 2011dh-The first 100 days2014In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 562, p. A17-, article id A17Article in journal (Refereed)
    Abstract [en]

    We present optical and near-infrared (NIR) photometry and spectroscopy of the Type IIb supernova (SN) 2011dh for the first 100 days. We complement our extensive dataset with Swift ultra-violet (UV) and Spitzer mid-infrared (MIR) data to build a UV to MIR bolometric lightcurve using both photometric and spectroscopic data. Hydrodynamical modelling of the SN based on this bolometric lightcurve have been presented in Bersten et al. (2012, ApJ, 757, 31). We find that the absorption minimum for the hydrogen lines is never seen below similar to 11 000 km s(-1) but approaches this value as the lines get weaker. This suggests that the interface between the helium core and hydrogen rich envelope is located near this velocity in agreement with the Bersten et al. (2012) He4R270 ejecta model. Spectral modelling of the hydrogen lines using this ejecta model supports the conclusion and we find a hydrogen mass of 0.01-0.04 M-circle dot to be consistent with the observed spectral evolution. We estimate that the photosphere reaches the helium core at 5-7 days whereas the helium lines appear between similar to 10 and similar to 15 days, close to the photosphere and then move outward in velocity until similar to 40 days. This suggests that increasing non-thermal excitation due to decreasing optical depth for the gamma-rays is driving the early evolution of these lines. The Spitzer 4.5 mu m band shows a significant flux excess, which we attribute to CO fundamental band emission or a thermal dust echo although further work using late time data is needed. The distance and in particular the extinction, where we use spectral modelling to put further constraints, is discussed in some detail as well as the sensitivity of the hydrodynamical modelling to errors in these quantities. We also provide and discuss pre- and post-explosion observations of the SN site which shows a reduction by similar to 75 percent in flux at the position of the yellow supergiant coincident with SN 2011dh. The B, V and r band decline rates of 0.0073, 0.0090 and 0.0053 mag day(-1) respectively are consistent with the remaining flux being emitted by the SN. Hence we find that the star was indeed the progenitor of SN 2011dh as previously suggested by Maund et al. (2011, ApJ, 739, L37) and which is also consistent with the results from the hydrodynamical modelling.

  • 43.
    Ergon, Mattias
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stritzinger, Maximilian
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hydrodynamical modelling of Type IIb SNeIn: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746Article in journal (Refereed)
  • 44. Fox, Ori D.
    et al.
    Bostroem, K. Azalee
    Van Dyk, Schuyler D.
    Filippenko, Alexei V.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Matheson, Thomas
    Cenko, S. Bradley
    Chandra, Poonam
    Dwarkadas, Vikram
    Li, Weidong
    Parker, Alex H.
    Smith, Nathan
    UNCOVERING THE PUTATIVE B-STAR BINARY COMPANION OF THE SN 1993J PROGENITOR2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 790, no 1, p. 17-Article in journal (Refereed)
    Abstract [en]

    The Type IIb supernova (SN) 1993J is one of only a few stripped-envelope SNe with a progenitor star identified in pre-explosion images. SN IIb models typically invoke H envelope stripping by mass transfer in a binary system. For the case of SN 1993J, the models suggest that the companion grew to 22M(circle dot) and became a source of ultraviolet (UV) excess. Located in M81, at a distance of only 3.6 Mpc, SN 1993J offers one of the best opportunities to detect the putative companion and test the progenitor model. Previously published near-UV spectra in 2004 showed evidence for absorption lines consistent with a hot (B2 Ia) star, but the field was crowded and dominated by flux from the SN. Here we present Hubble Space Telescope Cosmic Origins Spectrograph and Wide-Field Camera 3 observations of SN 1993J from 2012, at which point the flux from the SN had faded sufficiently to potentially measure the UV continuum properties from the putative companion. The resulting UV spectrum is consistent with contributions from both a hot B star and the SN, although we cannot rule out line-of-sight coincidences.

  • 45. France, Kevin
    et al.
    McCray, Richard
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, Josefin
    Frank, Kari A.
    Burrows, David N.
    Challis, Peter
    Kirshner, Robert P.
    Chevalier, Roger A.
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Smith, Nathan
    Sonneborn, George
    MAPPING HIGH-VELOCITY H alpha AND Ly alpha EMISSION FROM SUPERNOVA 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L16Article in journal (Refereed)
    Abstract [en]

    We present new Hubble Space Telescope images of high-velocity H alpha and Ly alpha emission in the outer debris of SN 1987 A. The Ha images are dominated by emission from hydrogen atoms crossing the reverse shock (RS). For the first time we observe emission from the RS surface well above and below the equatorial. ring (ER), suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H alpha imaging, we measure the mass flux of hydrogen atoms crossing the RS front, in the velocity intervals (-7500 < V-obs < -2800 km s(-1)) and (1000 < V-obs < 7500 km s(-1)), (M)(H) over dot = 1.2 x 10(-3) M-circle dot yr(-1). We also present the first Ly alpha imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Ly alpha and X-ray emission, we observe that the majority of the high-velocity Ly alpha emission originates interior to the ER. The observed Ly alpha/H alpha photon ratio, < R(L alpha/H alpha)> approximate to 17, is significantly higher than the theoretically predicted ratio of approximate to 5 for neutral atoms crossing the RS front. We attribute this excess to Ly alpha emission produced by X-ray heating of the outer debris. The spatial orientation of the Ly alpha and X-ray emission suggests that X-ray heating of the outer debris is the dominant Ly alpha production mechanism in SN 1987 A at this phase in its evolution.

  • 46. France, Kevin
    et al.
    McCray, Richard
    Heng, Kevin
    Kirshner, Robert P.
    Challis, Peter
    Bouchet, Patrice
    Crotts, Arlin
    Dwek, Eli
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Garnavich, Peter M.
    Larsson, Josefin
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lawrence, Stephen S.
    Lundqvist, Peter
    Panagia, Nino
    Pun, Chun S. J.
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Stocke, John T.
    Wang, Lifan
    Wheeler, J. Craig
    Observing Supernova 1987A with the Refurbished Hubble Space Telescope2010In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 329, no 5999, p. 1624-1627Article in journal (Refereed)
    Abstract [en]

    Observations with the Hubble Space Telescope (HST), conducted since 1990, now offer an unprecedented glimpse into fast astrophysical shocks in the young remnant of supernova 1987A. Comparing observations taken in 2010 with the use of the refurbished instruments on HST with data taken in 2004, just before the Space Telescope Imaging Spectrograph failed, we find that the Ly alpha and H alpha lines from shock emission continue to brighten, whereas their maximum velocities continue to decrease. We observe broad, blueshifted Ly alpha, which we attribute to resonant scattering of photons emitted from hot spots on the equatorial ring. We also detect N v lambda lambda 1239, 1243 angstrom line emission, but only to the red of Ly alpha. The profiles of the N v lines differ markedly from that of H alpha, suggesting that the N4+ ions are scattered and accelerated by turbulent electromagnetic fields that isotropize the ions in the collisionless shock.

  • 47. France, Kevin
    et al.
    McCray, Richard
    Penton, Steven V.
    Kirshner, Robert P.
    Challis, Peter
    Laming, J. Martin
    Bouchet, Patrice
    Chevalier, Roger
    Garnavich, Peter M.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Heng, Kevin
    Larsson, Josefin
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Lawrence, Stephen
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Panagia, Nino
    Pun, Chun S. J.
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sonneborn, George
    Sugerman, Ben
    Wheeler, J. Craig
    HST-COS Observations of Hydrogen, Helium, Carbon, and Nitrogen Emission from the SN 1987A Reverse Shock2011In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, no 2, p. 186-Article in journal (Refereed)
    Abstract [en]

    We present the most sensitive ultraviolet observations of Supernova 1987A to date. Imaging spectroscopy from the Hubble Space Telescope-Cosmic Origins Spectrograph shows many narrow (Δv ~ 300 km s-1) emission lines from the circumstellar ring, broad (Δv ~ 10-20 × 103 km s-1) emission lines from the reverse shock, and ultraviolet continuum emission. The high signal-to-noise ratio (>40 per resolution element) broad Lyα emission is excited by soft X-ray and EUV heating of mostly neutral gas in the circumstellar ring and outer supernova debris. The ultraviolet continuum at λ > 1350 Å can be explained by H I two-photon (2s 2 S 1/2-1s 2 S 1/2) emission from the same region. We confirm our earlier, tentative detection of N V λ1240 emission from the reverse shock and present the first detections of broad He II λ1640, C IV λ1550, and N IV] λ1486 emission lines from the reverse shock. The helium abundance in the high-velocity material is He/H = 0.14 ± 0.06. The N V/Hα line ratio requires partial ion-electron equilibration (Te /Tp ≈ 0.14-0.35). We find that the N/C abundance ratio in the gas crossing the reverse shock is significantly higher than that in the circumstellar ring, a result that may be attributed to chemical stratification in the outer envelope of the supernova progenitor. The N/C abundance may have been stratified prior to the ring expulsion, or this result may indicate continued CNO processing in the progenitor subsequent to the expulsion of the circumstellar ring. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.

  • 48.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Challis, Peter M.
    Chevalier, Roger A.
    Filippenko, Alexei V.
    Kirshner, Robert P.
    Kozma, Cecilia
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leonard, Douglas C.
    Matheson, Thomas
    Baron, E.
    Garnavich, Peter
    Jha, Saurabh
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Pun, C. S. J.
    Wang, Lifan
    Wheeler, J. Craig
    Hubble Space Telescope and Ground-based Observations of SN 1993J and SN 1998S: CNO Processing in the Progenitors2005In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 622, p. 991-1007Article in journal (Refereed)
    Abstract [en]

    Ground-based and Hubble Space Telescope observations are presented for SN 1993J and SN 1998S. SN 1998S shows strong, relatively narrow circumstellar emission lines of N III-V and C III-IV, as well as broad lines from the ejecta. Both the broad ultraviolet and optical lines in SN 1998S indicate an expansion velocity of ~7000 km s-1. The broad emission components of Lyα and Mg II are strongly asymmetrical after day 72 past the explosion and differ in shape from Hα. Different models based on dust extinction from dust in the ejecta or shock region, in combination with Hα from a circumstellar torus, are discussed. It is concluded, however, that the double-peaked line profiles are more likely to arise as a result of optical depth effects in the narrow, cool, dense shell behind the reverse shock than in a torus-like region. The ultraviolet lines of SN 1993J are broad, with a boxlike shape, coming from the ejecta and a cool, dense shell. The shapes of the lines are well fitted by a shell with inner velocity ~7000 km s-1 and outer velocity ~10,000 km s-1. For both SN 1993J and SN 1998S a strong nitrogen enrichment is found, with N/C~12.4 in SN 1993J and N/C~6.0 in SN 1998S. From a compilation of all supernovae with determined CNO ratios, we discuss the implications of these observations for the structure of the progenitors of Type II supernovae. Based in part on observations obtained with the Hubble Space Telescope, which is operated by AURA, Inc., under NASA contract NAS 5-26555.

  • 49.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Challis, Peter J.
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Marion, G. H.
    Milisavljevic, Dan
    Smith, Nathan
    Bufano, Filomena
    Friedman, Andrew S.
    Kangas, Tuomas
    Larsson, Josefin
    Mattila, Seppo
    Benetti, Stefano
    Chornock, Ryan
    Czekala, Ian
    Söderberg, Alicia
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    HIGH-DENSITY CIRCUMSTELLAR INTERACTION IN THE LUMINOUS TYPE IIn SN 2010jl: THE FIRST 1100 DAYS2014In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 797, no 2, article id 118Article in journal (Refereed)
    Abstract [en]

    Hubble Space Telescope and ground-based observations of the Type IIn supernova (SN) 2010jl are analyzed, including photometry and spectroscopy in the ultraviolet, optical, and near-IR bands, 26-1128 days after first detection. At maximum, the bolometric luminosity was similar to 3 x 10(43) erg s(-1) and even at 850 days exceeds 10(42) erg s(-1). A near-IR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is greater than or similar to 6.5x10(50) erg, excluding the dust component. The spectral lines can be separated into one broad component that is due to electron scattering and one narrow with expansion velocity similar to 100 km s(-1) from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after similar to 50 days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large-scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an r(-2) CSM with a mass-loss rate of M similar to 0.1 M(circle dot)yr(-1). The total mass lost is greater than or similar to 3 M-circle dot. These properties are consistent with the SN expanding into a CSM characteristic of a luminous blue variable progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM that is still opaque to electron scattering.

  • 50.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Gröningsson, Per
    Stockholm University, Faculty of Science, Department of Astronomy.
    Twenty Years of Supernova 1987A2007In: The Messenger, Vol. 127, no 44Article in journal (Other (popular science, discussion, etc.))
12345 1 - 50 of 203
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