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• 1551. Vannuccini, E.
KTH, Skolan för teknikvetenskap (SCI), Fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Measurement of Lithium and Beryllium cosmic-ray abundances by the PAMELA experiment2015Inngår i: Proceedings of Science, Proceedings of Science (PoS) , 2015Konferansepaper (Fagfellevurdert)

The PAMELA experiment is collecting particles along a low Earth semi-polar orbit on board of Resurs-DK1 satellite since June 2006. The combined information of a silicon tracking system and a scintillator hodoscope provides redundant light-element identification capabilities, via multiple ionization energy-loss measurements. The instrument design is not optimized for nuclei detection, whose high ionization signal progressively saturates the detectors. However, Li and Be nuclei can still be identified by using the full set of information, which allows to efficiently select the two elements against the background of more abundant elements. The main issues of the analysis aiming to optimize the Li and Be selection are discussed in this paper. Preliminary results on the elemental abundances will be presented at the conference.

• 1552. Vianello, G.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
The multi-mission maximum likelihood framework (3ML)2015Inngår i: Proceedings of Science, Proceedings of Science (PoS) , 2015Konferansepaper (Fagfellevurdert)

Astrophysical sources are now observed by many different instruments at different wavelengths, from radio to high-energy gamma-rays, with an unprecedented quality. Putting all these data together to form a coherent view, however, is a very difficult task. Each instrument has its own data format, software and analysis procedure, which are difficult to combine. It is for example very challenging to perform a broadband fit of the energy spectrum of the source. The Multi-Mission Maximum Likelihood framework (3ML) aims to solve this issue, providing a common framework which allows for a coherent modeling of sources using all the available data, independent of their origin. At the same time, thanks to its architecture based on plug-ins, 3ML uses the existing official software of each instrument for the corresponding data in a way which is transparent to the user. 3ML is based on the likelihood formalism, in which a model summarizing our knowledge about a particular region of the sky is convolved with the instrument response and compared to the corresponding data. The user can choose between a frequentist analysis, and a Bayesian analysis. In the former, parameters of the model are optimized in order to obtain the best match to the data (i.e., the maximum of the likelihood). In the latter, the priors specified by the user are used to build the posterior distribution, which is then sampled with Markov Chain Monte Carlo or Multinest. Our implementation of this idea is very flexible, allowing the study of point sources as well as extended sources with arbitrary spectra. We will review the problem we aim to solve, the 3ML concepts and its innovative potential.

• 1553. Vianello, Giacomo
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
The Multi-Mission Maximum Likelihood framework (3ML)2015Manuskript (preprint) (Annet vitenskapelig)

Astrophysical sources are now observed by many different instruments at different wavelengths, from radio to high-energy gamma-rays, with an unprecedented quality. Putting all these data together to form a coherent view, however, is a very difficult task. Each instrument has its own data format, software and analysis procedure, which are difficult to combine. It is for example very challenging to perform a broadband fit of the energy spectrum of the source. The Multi-Mission Maximum Likelihood framework (3ML) aims to solve this issue, providing a common framework which allows for a coherent modeling of sources using all the available data, independent of their origin. At the same time, thanks to its architecture based on plug-ins, 3ML uses the existing official software of each instrument for the corresponding data in a way which is transparent to the user. 3ML is based on the likelihood formalism, in which a model summarizing our knowledge about a particular region of the sky is convolved with the instrument response and compared to the corresponding data. The user can choose between a frequentist analysis, and a Bayesian analysis. In the former, parameters of the model are optimized in order to obtain the best match to the data (i.e., the maximum of the likelihood). In the latter, the priors specified by the user are used to build the posterior distribution, which is then sampled with Markov Chain Monte Carlo or Multinest. Our implementation of this idea is very flexible, allowing the study of point sources as well as extended sources with arbitrary spectra. We will review the problem we aim to solve, the 3ML concepts and its innovative potential.

• 1554. Viesti, G.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Scanning cargo containers with tagged neutrons2007Inngår i: 7th Latin American Symposium on Nuclear Physics and Applications, American Institute of Physics (AIP), 2007, s. 57-62Konferansepaper (Fagfellevurdert)

A new Tagged Neutron Inspection System (TNIS) able to detect illicit materials such as explosives and narcotics in cargo containers has been developed within the EURopean Illicit TRAfficing Countermeasures Kit (EURITRACK) project. After the R&D phase, the inspection portal has been installed and commissioned at the Rijeka seaport in Croatia, where it has been operated in connection with the existing X-ray scanner for a first two-month demonstration campaign. Results obtained are presented and discussed in this paper.

• 1555.
Peking University.
Peking University. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik. Peking University. Peking University.
Alpha-particle decays from excited states in Mg-242011Inngår i: Science China: Physics, Mechanics and Astronomy, ISSN 1674-7348, Vol. 54, nr 1, s. S130-S135Artikkel i tidsskrift (Fagfellevurdert)

Using a cluster model based on the Woods-Saxon potential, alpha-particle decays from excited states in Mg-24 have been systematically investigated. Calculations can in general reproduce experimental data, noticing the fact that the preformation factor P of alpha particle in alpha-decaying nuclei is of order from 10(0) to 10(-2). This can be the evidence for the alpha+Ne-20 structure in Mg-24. Meanwhile, the results also show the existence of other configurations, such as O-16+2 alpha. Since the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster (alpha particle), our results could serve as a guide to experimental spin assignments.

• 1556. Wang, Xiang-Gao
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
HOW BAD OR GOOD ARE THE EXTERNAL FORWARD SHOCK AFTERGLOW MODELS OF GAMMA-RAY BURSTS?2015Inngår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 219, nr 1, artikkel-id 9Artikkel i tidsskrift (Fagfellevurdert)

• 1557. Weltevrede, P.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Gamma-ray and radio properties of six pulsars detected by the Fermi large area telescope2010Inngår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 708, nr 2, s. 1426-1441Artikkel i tidsskrift (Fagfellevurdert)

We report the detection of pulsed gamma-rays for PSRs J0631+1036, J0659+1414, J0742-2822, J1420-6048, J1509-5850, and J1718-3825 using the Large Area Telescope on board the Fermi Gamma-ray Space Telescope (formerly known as GLAST). Although these six pulsars are diverse in terms of their spin parameters, they share an important feature: their gamma-ray light curves are (at least given the current count statistics) single peaked. For two pulsars, there are hints for a double-peaked structure in the light curves. The shapes of the observed light curves of this group of pulsars are discussed in the light of models for which the emission originates from high up in the magnetosphere. The observed phases of the gamma-ray light curves are, in general, consistent with those predicted by high-altitude models, although we speculate that the gamma-ray emission of PSR J0659+1414, possibly featuring the softest spectrum of all Fermi pulsars coupled with a very low efficiency, arises from relatively low down in the magnetosphere. High-quality radio polarization data are available showing that all but one have a high degree of linear polarization. This allows us to place some constraints on the viewing geometry and aids the comparison of the gamma-ray light curves with high-energy beam models.

• 1558.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Measurements of Cosmic Ray Antiprotons with PAMELA2010Licentiatavhandling, monografi (Annet vitenskapelig)
• 1559.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Measurements of cosmic ray antiprotons with PAMELA and studies of propagation models2012Doktoravhandling, monografi (Annet vitenskapelig)

Studying the acceleration and propagation mechanisms of Galactic cosmic rays can provide information regarding astrophysical sources, the properties of our Galaxy, and possible exotic sources such as dark matter. To understand cosmic ray acceleration and propagation mechanisms, accurate measurements of different cosmic ray elements over a wide energy range are needed. The PAMELA experiment is a satellite-borne apparatus which allows different cosmic ray species to be identified over background.

Measurements of the cosmic ray antiproton flux and the antiproton-to-proton flux ratio from 1.5 GeV to 180 GeV are presented in this thesis, employing the data collected between June 2006 and December 2008. Compared to previous experiments, PAMELA extends the energy range of antiproton measurements and provides significantly higher statistics. During about 800 days of data collection, PAMELA identified approximately 1300 antiprotons including 61 above 31.7 GeV. A dramatic improvement of statistics is evident since only 2 events above 30 GeV are reported by previous experiments. The derived antiproton flux and antiproton-to-proton flux ratio are consistent with previous measurements and generally considered to be produced as secondary products when cosmic ray protons and helium nuclei interact with the interstellar medium.

To constrain cosmic ray acceleration and propagation models, the antiproton data measured by PAMELA were further used together with the proton spectrum reported by PAMELA, as well as the B/C data provided by other experiments. Statistical tools were interfaced with the cosmic ray propagation package GALPROP to perform the constraining analyses.

Different diffusion models were studied. It was shown in this work that only current PAMELA data, i.e. the antiproton-to-proton ratio and the proton flux, are not able to place strong constraints on propagation parameters. Diffusion models with a linear diffusion coefficient and modified diffusion models with a low energy dependence of the diffusion coefficient were studied in the $\chi^{2}$ study. Uncertainties on the parameters and the goodness of fit of each model were given. Some models are further studied using the Bayesian inference. Posterior means and errors of the parameters base on our prior knowledge on them were obtained in the Bayesian framework. This method also allowed us to understand the correlation between parameters and compare models.

Since the B/C ratio used in this analysis is from experiments other than PAMELA, future PAMELA secondary-to-primary ratios (B/C, $^{2}$H/$^{4}$He and $^{3}$He/$^{4}$He) can be used to avoid the data sets inconsistencies between different experiments and to minimize uncertainties on the solar modulation parameters. More robust and tighter constraints are expected. The statistical techniques have been demonstrated useful to constrain models and can be extended to other observations, e.g. electrons, positrons, gamma rays etc. Using these channels, exotic contributions from, for example, dark matter will be further investigated in future.

• 1560.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Measurements of cosmic-ray antiprotons with PAMELA2011Inngår i: Astrophysics and Space Sciences Transactions (ASTRA), ISSN 1810-6528, E-ISSN 1810-6536, Vol. 7, nr 2, s. 225-228Artikkel i tidsskrift (Fagfellevurdert)

The PAMELA experiment is a satellite-borne apparatus designed to study charged particles, and especially antiparticles, in the cosmic radiation. The apparatus is mounted on the Resurs DK1 satellite which was launched on 15 June 2006. PAMELA has been traveling around the earth along an elliptical and semi-polar orbit for almost five years. It mainly consists of a permanent magnetic spectrometer, a time of flight system and an electromagnetic imaging calorimeter, which allows antiprotons to be identified from a dominating cosmic-ray background. New measurements of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio between 60 MeV and 180 GeV are presented, employing data collected between June 2006 and December 2008. Compared to previous experiments, PAMELA extends the energy range of antiproton measurements and provides significantly higher statistics. The derived antiproton flux and antiproton-to-proton flux ratio indicates that the main source of cosmic-ray antiprotons is considered to be secondary production and no primary contribution has to be invoked.

• 1561.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Oskar Klein Centre for Cosmoparticle Physics, Sweden .
LPSC, UJF Grenoble 1, CNRS/IN2P3, INP de Grenoble, France. Department of Physics, Stockholm University. Oskar Klein Centre for Cosmoparticle Physics, Sweden.
Constraints on cosmic-ray propagation and acceleration models from recent data2011Inngår i: Proceedings of the 32nd International Cosmic Ray Conference, ICRC 2011, Institute of High Energy Physics , 2011, Vol. 6, s. 228-231Konferansepaper (Fagfellevurdert)

We are studying the constraints obtained on transport and acceleration mechanisms of galactic cosmic rays by using statistical tools in combination with the propagation package GALPROP and recent PAMELA data. Using only PAMELA data allows us to avoid inconsistencies between data sets from different experiments, minimise uncertainties on solar modulation parameters, and have a complementary and precise data set on (anti-)matter as well as primary and secondary nuclei over 3 orders of magnitude in energy. This allows us to simultaneously place strong constraints on cosmic-ray propagation and acceleration models. We describe our methodology and present some preliminary results in this paper.

• 1562. Wu, X.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
PANGU: A Wide Field Gamma-Ray Imager and Polarimeter2016Inngår i: SPACE TELESCOPES AND INSTRUMENTATION 2016: ULTRAVIOLET TO GAMMA RAY, SPIE - International Society for Optical Engineering, 2016, artikkel-id UNSP 99056EKonferansepaper (Fagfellevurdert)

PANGU (the PAir-productioN Gamma-ray Unit) is a gamma-ray telescope with a wide field of view optimized for spectro-imaging, timing and polarization studies. It will map the gamma-ray sky from 10 MeV to a few GeV with unprecedented spatial resolution. This window on the Universe is unique to detect photons produced directly by relativistic particles, via the decay of neutral pions, or the annihilation or decay light from anti-matter and the putative light dark matter candidates. A wealth of questions can be probed among the most important themes of modern physics and astrophysics. The PANGU instrument is a pair-conversion gamma-ray telescope based on an innovative design of a silicon strip tracker. It is light, compact and accurate. It consists of 100 layers of silicon micro-strip detectors of 80 x 80 cm(2) in area, stacked to height of about 90 cm, and covered by an anticoincidence detectors. PANGU relies on multiple scattering effects for energy measurement, reaching an energy resolution between 30-50% for 10 MeV - 1GeV. The novel tracker will allow the first polarization measurement and provide the best angular resolution ever obtained in the soft gamma ray and GeV band.

• 1563. Wuf, X.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
PANGU: A high resolution gamma-ray space telescope2015Inngår i: Proceedings of Science, Proceedings of Science (PoS) , 2015Konferansepaper (Fagfellevurdert)

PANGU (the PAir-productioN Gamma-ray Unit) is a small astrophysics mission with wide field of view optimized for spectro-imaging, timing and polarisation studies. It will map the gamma-ray sky from 10 MeV to a few GeV with unprecedented spatial resolution. This window on the Universe is unique to detect photons emitted directly by relativistic particles, via the decay of neutral pions, or the annihilation or decay light from anti-matter and the putative light dark matter candidates. A wealth of questions can be probed among the most important themes of modern physics and astrophysics. The PANGU instrument is a pair-conversion gamma-ray telescope based on an innovative design of a silicon strip tracker. It is light, compact and accurate. It consists of 100 layers of silicon micro-strip detector of 40 x 40 cm2 in area, stacked to height of about 90 cm, and covered by a top anticoincidence detector. PANGU relies on multiple scattering effects for energy measurement, reaching an energy resolution between 30-50% for 10 MeV - 1 GeV. The novel tracker will allow the first polarisation measurement and provide the best angular resolution ever obtained in the soft gamma ray and GeV band. PANGU has been proposed to the recent ESA-CAS Call for Joint Small Science Mission. In this contribution, the key science objectives, the payload concept and the expected performance will be presented.

• 1564.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden..
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. AlbaNova Univ Ctr, Oskar Klein Ctr Cosmoparticle Phys, S-10691 Stockholm, Sweden.
A Study of Background Conditions for Sphinx-The Satellite-Borne Gamma-Ray Burst Polarimeter2018Inngår i: Galaxies, E-ISSN 2075-4434, Vol. 6, nr 2, artikkel-id 50Artikkel i tidsskrift (Fagfellevurdert)

SPHiNX is a proposed satellite-borne gamma-ray burst polarimeter operating in the energy range 50-500 keV. The mission aims to probe the fundamental mechanism responsible for gamma-ray burst prompt emission through polarisation measurements. Optimising the signal-to-background ratio for SPHiNX is an important task during the design phase. The Geant4 Monte Carlo toolkit is used in this work. From the simulation, the total background outside the South Atlantic Anomaly (SAA) is about 323 counts/s, which is dominated by the cosmic X-ray background and albedo gamma rays, which contribute similar to 60% and similar to 35% of the total background, respectively. The background from albedo neutrons and primary and secondary cosmic rays is negligible. The delayed background induced by the SAA-trapped protons is about 190 counts/s when SPHiNX operates in orbit for one year. The resulting total background level of similar to 513 counts/s allows the polarisation of similar to 50 GRBs with minimum detectable polarisation less than 30% to be determined during the two-year mission lifetime.

• 1565.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
Multistep shell model description of spin-aligned neutron-proton pair coupling2012Inngår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 877, s. 51-58Artikkel i tidsskrift (Fagfellevurdert)

The recently proposed spin-aligned neutron-proton pair coupling scheme is studied within a non-orthogonal basis in term of the multistep shell model. This allows us to identify simultaneously the roles played by other configurations such as the normal pairing term. The model is applied to four-, six- and eight-hole N = Z nuclei below the core Sn-100.

• 1566.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
Multistep shell model in the complex energy plane2012Inngår i: Advanced Many-Body And Statistical Methods In Mesoscopic Systems, Institute of Physics Publishing (IOPP), 2012, s. 012029-Konferansepaper (Fagfellevurdert)

We have adopted the multistep shell model in the complex energy plane to study nuclear excitations occurring in the continuum part of the spectrum. In this method one proceeds by solving the shell model equations in a successive manner. That is, in each step one constructs the building blocks to be used in future steps. We applied this formalism to analyze the unbound nuclei Li-12,Li-13 starting from the one - particle states in Li-10 and two - particle states in Li-11. In the former case the excitations correspond to the motion of three particles partitioned as the product of a one - particle and two - particle systems. The ground state of Li-12 is thus calculated to be an antibound (virtual) state. In the four - particle system Li-13 the states can be constructed as the coupling of two correlated pairs. We found that there is no bound or antibound state in Li-13.

• 1567.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik. GANIL, France. GANIL, France. GANIL, France. KTH, Skolan för teknikvetenskap (SCI), Fysik, Kärnfysik.
Analysis of the unbound spectrum of 12Li.2011Inngår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 850, s. 53-68Artikkel i tidsskrift (Fagfellevurdert)

The unbound nucleus 12Li is evaluated by studying three-neutron one-proton excitations within the multistepshell model in the complex energy plane. It is found that the ground state of this system consists of anantibound 2− state. A number of narrow states at low energy are found which ensue from the coupling ofresonances in 11Li to continuum states close to threshold.

• 1568.
Tokyo Metropolitan Univ, Dept Phys, 1-1 Minami Osawa, Hachioji, Tokyo 1920397, Japan..
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. Tokyo Metropolitan Univ, Dept Phys, 1-1 Minami Osawa, Hachioji, Tokyo 1920397, Japan.. Tokyo Metropolitan Univ, Dept Phys, 1-1 Minami Osawa, Hachioji, Tokyo 1920397, Japan.. Tokyo Metropolitan Univ, Dept Phys, 1-1 Minami Osawa, Hachioji, Tokyo 1920397, Japan.. Tokyo Metropolitan Univ, Dept Phys, 1-1 Minami Osawa, Hachioji, Tokyo 1920397, Japan.. NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA.;Lawrence Livermore Natl Lab, 7000 East Ave, Livermore, CA 94550 USA.. NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA.;Lawrence Livermore Natl Lab, 7000 East Ave, Livermore, CA 94550 USA.. NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA.;Lawrence Livermore Natl Lab, 7000 East Ave, Livermore, CA 94550 USA.. NASA, Goddard Space Flight Ctr, 8800 Greenbelt Rd, Greenbelt, MD 20771 USA.;Lawrence Livermore Natl Lab, 7000 East Ave, Livermore, CA 94550 USA.. Yale Univ, Dept Phys, POB 208120, New Haven, CT 06520 USA.. Yale Univ, Dept Phys, POB 208120, New Haven, CT 06520 USA..
Poisson vs. Gaussian statistics for sparse X-ray data: Application to the soft X-ray spectrometer2019Inngår i: Publications of the Astronomical Society of Japan, ISSN 0004-6264, E-ISSN 2053-051X, Vol. 71, nr 4, artikkel-id 75Artikkel i tidsskrift (Fagfellevurdert)

Reliable results when fitting X-ray data require proper consideration of the statistics involved. We probe the impact of Gaussian versus Poisson statistics at low count levels using both the standard chi(2) method and maximum likelihood based on Poisson studied and quantified through simulated spectra with known properties. We then test the results through analysis of Mn K alpha calibration data taken with the flight spare microcalorimeter for the Hitomi soft X-ray spectrometer. Through comparison with simulations, our results show that the chi(2) method tends to give overly optimistic estimates of the detector energy resolution, in particular when there are few counts. Given an energy resolution of similar to 5eV and a line with about 100 photons, the line width becomes similar to 10% lower in the chi(2) method than in Poisson statistics. This is a consequence of the uncertainties being dominated by counting statistics, and therefore highlights the need to choose the appropriate fit statistic.

• 1569.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Annihilation Lines from Dark Matter with the Fermi-LAT2010Inngår i: Invisible Universe International Conference, 2010, s. 463-467Konferansepaper (Fagfellevurdert)

Dark matter is today one of the most intriguing but so far unresolved issues in physics. Many extensions of the Standard Model of particle physics predict a stable Weakly Interacting Massive Particle (WIMP) that may annihilate directly into two gamma-rays. If the WIMPs are non-relativistic, the gamma-rays from this channel will have an energy equal to the mass of the WIMP. The signature caused by this annihilation is a spectral line, smeared out only by the energy resolution of the detector. The signal would be a "smoking gun" for dark matter, since no other astrophysical source should be able to produce it. We present here the preliminary results from the search for a dark matter line on a limited data set from the Fermi Large Area Telescope (LAT), the main instrument onboard the Fermi Gamma-ray Space Telescope, which was successfully launched on June 11, 2008. The Fermi-LAT is a pair-conversion detector for gamma-rays with an energy range from 20 MeV to 300 GeV and has an unprecedented resolution and sensitivity.

• 1570.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Search for Gamma-ray Lines from Dark Matter with the Fermi Large Area Telescope2010Doktoravhandling, monografi (Annet vitenskapelig)

Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate. One of the most interesting scenarios is the creation of monochromatic gamma-rays from the annihilation or decay of these particles. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it.

In this thesis, the search for spectral lines with the Large Area Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope (Fermi) is presented. The satellite was successfully launched from Cape Canaveral in Florida, USA, on 11 June, 2008. The energy resolution and performance of the detector are both key factors in the search and are investigated here using beam test data, taken at CERN in 2006 with a scaled-down version of the Fermi-LAT instrument. A variety of statistical methods, based on both hypothesis tests and confidence interval calculations, are then reviewed and tested in terms of their statistical power and coverage.

A selection of the statistical methods are further developed into peak finding algorithms and applied to a simulated data set called obssim2, which corresponds to one year of observations with the Fermi-LAT instrument, and to almost one year of Fermi-LAT data in the energy range 20–300 GeV. The analysis on Fermi-LAT data yielded no detection of spectral lines, so limits are placed on the velocity-averaged cross-section, $<\sigma v>_{\gamma X}$, and the decay lifetime, $\tau_{\gamma X}$, and theoretical implications are discussed.

• 1571.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Towards detecting lines from dark matter annihilations with GLAST2008Licentiatavhandling, monografi (Annet vitenskapelig)

Dark matter (DM) constitutes one of the most intriguing but so far unresolved issues in physics. In many extensions of the Standard Model of particle physics, the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent DM particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and will manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a “smoking gun” for DM, since no other known astrophysical process should be able to produce it. When searching for a line, the energy resolution and performance of the calorimeter are key factors. In this thesis, these are investigated using beam test data, taken at CERN in 2006. Four statistical methods that can be used to search for DM spectral lines are, then, studied in terms of their power and coverage. The methods are based on both hypothesis tests and confidence interval calculations. Two peak finding methods are also tested on a simulated data set representing one year of realistic data, obtained with the Large Area Telescope (LAT) on-board the Gamma-ray Large Area Space Telescope (GLAST). The data set is called Service Challenge 2 (SC2) and contains a variety of gamma-ray sources, including different DM components. Finally, an upper limit on < σν > γγ, based on SC2, is calculated.

• 1572. Yu, Hoi-Fung
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Synchrotron cooling in energetic gamma-ray bursts observed by the Fermi Gamma-Ray Burst Monitor2015Inngår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 573, artikkel-id A81Artikkel i tidsskrift (Fagfellevurdert)

Context. We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor ((IBM) onboard the Fermi Gamma-Ray Space Telescope. Aims. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Methods. Our sample comprises eight GRBs observed by the Fermi (IBM in its first five years of mission, with 1 keV-1 MeV fluence f > 1.0 x 10(-4) erg cm(-2) and a signal-to-noise ratio level of S/N >= 10.0 above 900 keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-lay index alpha, the high-energy power-law index beta, the peak energy in the observed nu F-nu, spectrum E-p, and the difference between the low- and high-energy power-law indices Delta s = alpha-beta. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies E-b,E-1 and E-b,E-2 the middle segment power-law index beta, and the Planck function temperature kT. Results. The Band function parameter distributions are alpha = -0.73(-0.21)(+0.16), beta = -2.13(-0.56)(+0.28), E-p = 374.47(-187.7)(+307.3) keV (log(10) E-p = 2.577(-0.30)(+0.26)), and Delta s = 1.38(-0.31)(+0.54), with average errors sigma(alpha) similar to 0.1, sigma(beta) similar to 0.2, and sigma(Ep) similar to 0.1E(p). Using the distributions of Delta s and beta, the electron population index p is found to be consistent with the "moderately fast" scenario, in which fast- and slow-cooling scenarios cannot be distinguished. The physically motivated synchrotron-fitting function parameter distributions are E-b,E-1 = 129.6(-32.4)(+132.2) keV, E-b,E-2 = 631.4(-309.6)(+582) keV, beta = 1.721(-0.25)(+0.48), and kT = 10.4(-3.7)(+4.9) keV, with average errors sigma(beta) similar to 0.2, sigma E-b,E-1 similar to 0.1E(b,1), sigma E-b,E-2 similar to 0.4E(b,2,) and sigma(kT) similar to 0.1kT. This synchrotron function requires the synchrotron injection and cooling break (i.e., E-min and E-cool) to be close to each other within a factor of ten, often in addition to a Planck function. Conclusions. A synchrotron model is found that is consistent with most of the time-resolved spectra for eight energetic Fermi (IBM bursts with good high-energy photon statistics as long as both the cooling and injection break are included and the leftmost spectral slope is lifted either by including a thermal component or when an evolving magnetic field is accounted for.

• 1573. Yurkin, Yu.T.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Energi- och ugnsteknik.
Trapped antiprotons in the Earth inner radiation belt in PAMELA experiment2011Inngår i: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 75, nr 6, s. 854-856Artikkel i tidsskrift (Fagfellevurdert)

The existence of trapped antiprotons in the Earth's inner radiation belt has been theoretically predicted, but not observed. We present a procedure for antiproton selection and the observation results from the PAMELA space experiment measurements. The PAMELA magnetic spectrometer ensures reliable identification of particles and charge signs, value determination, and energy measurement, thus enabling us to experimentally establish the existence of antiprotons trapped in the Earth's inner radiation belt.

• 1574. Zaconte, V.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
ALTEA: flight model calibration at GSI2006Inngår i: Advances in Space Research, ISSN 0273-1177, E-ISSN 1879-1948, Vol. 37, nr 9, s. 1704-1709Artikkel i tidsskrift (Fagfellevurdert)

The ALTEA project, an international and multi-disciplinary collaboration scheduled to fly in the International Space Station (ISS) after July 2006, is aimed at studying particle radiation in space environment and its effects on astronauts, in particular the anomalous perception of 'light flashes'. In this paper, we present experimental results obtained by testing the Flight Model of the ALTEA particle detector in two measurement sessions performed at the heavy ion accelerator of GSI laboratory in Darmstadt, Germany. Instrument response was compared with Monte-carlo simulations to study its linearity and calculate amplification.

• 1575. Zane, Silvia
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
The on-board calibration system of the X-ray Imaging Polarimetry Explorer (XIPE)2016Inngår i: SPACE TELESCOPES AND INSTRUMENTATION 2016: ULTRAVIOLET TO GAMMA RAY, SPIE - International Society for Optical Engineering, 2016, artikkel-id UNSP 99054HKonferansepaper (Fagfellevurdert)

The calibration system for XIPE is aimed at providing a way to check and correct possible variations of performance of the Gas Pixel Detector during the three years of operation in orbit (plus two years of possible extended operation), while facilitating the observation of the celestial sources. This will be performed by using a filter wheel with a large heritage having a set of positions for the calibration and the observation systems. In particular, it will allow for correcting possible gain variation, for measuring the modulation factor using a polarized source, for removing non interesting bright sources in the field of view and for observing very bright celestial sources. The on-board calibration system is composed of three filter wheels, one for each detector and it is expected to operate for a small number of times during the year. Moreover, since it operates once at a time, within the observation mode, it allows for simultaneous calibration and acquisition from celestial sources on different detectors. In this paper we present the scope and the requirements of the on-board calibration system, its design, and a description of its possible use in space.

• 1576. Zhang, S. -N
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Introduction to the high energy cosmic-radiation detection (HERD) facility onboard China's future space station2017Inngår i: Proceedings of Science, Sissa Medialab Srl , 2017Konferansepaper (Fagfellevurdert)

The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads onboard China's Space Station, which is planned for operation starting around 2025 for about 10 years. The main scientific objectives of HERD are searching for signals of dark matter annihilation products, precise cosmic electron (plus positron) spectrum and anisotropy measurements up to 10 TeV, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is composed of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 7,500 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. The top STK microstrips of six X-Y layers are sandwiched with tungsten converters to make precise directional measurements of incoming electrons and gamma-rays. In the baseline design, each of the four side STKs is made of only three layers microstrips. All STKs will also be used for measuring the charge and incoming directions of cosmic rays, as well as identifying back scattered tracks. With this design, HERD can achieve the following performance: energy resolution of 1% for electrons and gamma-rays beyond 100 GeV and 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10-5; effective geometrical factors of &gt;3 m2sr for electron and diffuse gamma-rays, &gt;2 m2sr for cosmic ray nuclei. R&amp;D is under way for reading out the LYSO signals with optical fiber coupled to image intensified IsCMOS and CALO prototype of 250 LYSO crystals.

• 1577. Zhang, S. N.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
The high energy cosmic-radiation detection (HERD) facility onboard China's Space Station2014Inngår i: Proceedings of SPIE - The International Society for Optical Engineering, 2014Konferansepaper (Fagfellevurdert)

The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads of the cosmic lighthouse program onboard China's Space Station, which is planned for operation starting around 2020 for about 10 years. The main scientific objectives of HERD are indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is composed of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 104 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. The top STK microstrips of seven X-Y layers are sandwiched with tungsten converters to make precise directional measurements of incoming electrons and gamma-rays. In the baseline design, each of the four side SKTs is made of only three layers microstrips. All STKs will also be used for measuring the charge and incoming directions of cosmic rays, as well as identifying back scattered tracks. With this design, HERD can achieve the following performance: energy resolution of 1% for electrons and gamma-rays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10-5; effective geometrical factors of &gt;3 m2sr for electron and diffuse gamma-rays, &gt;2 m2sr for cosmic ray nuclei. R and D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD and the prototype of one layer of CALO. © 2014 SPIE.

• 1578.
SUNY Stony Brook, Dept Chem, Stony Brook, NY 11794 USA..
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik. CERN, Geneva, Switzerland..
Flow fluctuations in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector2019Inngår i: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 982, s. 323-326Artikkel i tidsskrift (Fagfellevurdert)

Measurements of four-particle cumulants c(n){4} for n = 1, 2, 3, 4 are presented using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of single harmonics p(v(n)). For the first time, a negative c(1){4} is observed. The c(4){4} is found to be negative in central collisions but changes sign around 20-25% centrality. This behavior is consistent with a nonlinear contribution to v(4) that is proportional to v(2)(2). c(2){4} and c(3){4} are calculated using two reference event classes in order to investigate the influence of volume fluctuations. Over most of the centrality range, c(2){4} and c(3){4} are found to be negative, while in the ultra-central collisions, c(2){4} changes sign and becomes positive, suggesting a deviation from Gaussian behavior in the event-by-event fluctuation of v(2). The magnitudes of the sign change are also found to be dependent of the event class definition .

• 1579. Řípa, J.
KTH, Skolan för teknikvetenskap (SCI), Fysik, Partikel- och astropartikelfysik.
Cosmological effects on the observed flux and fluence distributions of gamma-ray bursts2011Konferansepaper (Fagfellevurdert)

Several claims have been put forward that an essential fraction of long-duration BATSE gamma-ray bursts should lie at redshifts larger than 5. This point-of-view follows from the natural assumption that fainter objects should, on average, lie at larger redshifts. However, redshifts larger than 5 are rare for bursts observed by Swift. The purpose of this article is to show that the most distant bursts in general need not be the faintest ones. We derive the cosmological relationships between the observed and emitted quantities, and arrive at a prediction that is tested on the ensembles of BATSE, Swift and Fermi bursts. This analysis is independent on the assumed cosmology, on the observational biases, as well as on any gamma-ray burst model. We arrive to the conclusion that apparently fainter bursts need not, in general, lie at large redshifts. Such a behaviour is possible, when the luminosities (or emitted energies) in a sample of bursts increase more than the dimming of the observed values with redshift. In such a case dP(z)/dz > 0 can hold, where P(z) is either the peak-flux or the fluence. This also means that the hundreds of faint, long-duration BATSE bursts need not lie at high redshifts, and that the observed redshift distribution of long Swift bursts might actually represent the actual distribution.

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