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Supernovae seen through gravitational telescopes
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Astroparticle Physics and String Theory)ORCID iD: tanja.petrushevska@fysik.su.se
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Galaxies, and clusters of galaxies, can act as gravitational lenses and magnify the light of objects behind them. The effect enables observations of very distant supernovae, that otherwise would be too faint to be detected by existing telescopes, and allows studies of the frequency and properties of these rare phenomena when the universe was young. Under the right circumstances, multiple images of the lensed supernovae can be observed, and due to the variable nature of the objects, the difference between the arrival times of the images can be measured. Since the images have taken different paths through space before reaching us, the time-differences are sensitive to the expansion rate of the universe. One class of supernovae, Type Ia, are of particular interest to detect. Their well known brightness can be used to determine the magnification, which can be used to understand the lensing systems.

In this thesis, galaxy clusters are used as gravitational telescopes to search for lensed supernovae at high redshift. Ground-based, near-infrared and optical search campaigns are described of the massive clusters Abell 1689 and 370, which are among the most powerful gravitational telescopes known. The search resulted in the discovery of five photometrically classified, core-collapse supernovae at redshifts of 0.671<z<1.703 with significant magnification from the cluster. Owing to the power of the lensing cluster, the volumetric core-collapse supernova rates for 0.4 ≤ z < 2.9 were calculated, and found to be in good agreement with previous estimates and predictions from cosmic star formation history. During the survey, two Type Ia supernovae in A1689 cluster members were also discovered, which allowed the Type Ia explosion rate in galaxy clusters to be estimated. Furthermore, the expectations of finding lensed supernovae at high redshift in simulated search campaigns that can be conducted with upcoming ground- and space-based telescopes, are discussed.

Magnification from a galaxy lens also allows for detailed studies of the supernova properties at high redshift that otherwise would not be possible. Spectroscopic observations of lensed high-redshift supernovae Type Ia are of special interest since they can be used to test for evolution of the standard candle nature of these objects. If systematic redshift-dependent properties are found, their utility for future surveys could be challenged. In the thesis it is shown that the strongly lensed and very distant supernova Type Ia PS1-10afx at z=1.4, does not deviate from the well-studied nearby and intermediate populations of normal supernovae Type Ia.

In a different study, the discovery of the first resolved multiply-imaged gravitationally lensed supernova Type Ia is also reported.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University , 2017. , 66 p.
Keyword [en]
supernovae, strong gravitational lensing, star formation history, supernova rates
Keyword [sv]
supernovor Gravitationslins
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:su:diva-141633ISBN: 978-91-7649-797-5 (print)ISBN: 978-91-7649-798-2 (electronic)OAI: oai:DiVA.org:su-141633DiVA: diva2:1088540
Public defence
2017-05-29, sal FB42, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 10:15 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-05-04 Created: 2017-04-12 Last updated: 2017-05-05Bibliographically approved
List of papers
1. High-redshift supernova rates measured with the gravitational telescope A 1689
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2016 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 594, A54Article in journal (Refereed) Published
Abstract [en]

Aims. We present a ground-based, near-infrared search for lensed supernovae behind the massive cluster Abell 1689 at z = 0.18, which is one of the most powerful gravitational telescopes that nature provides. Methods. Our survey was based on multi-epoch J-band observations with the HAWK-I instrument on VLT, with supporting optical data from the Nordic Optical Telescope. Results. Our search resulted in the discovery of five photometrically classified, core-collapse supernovae with high redshifts of 0.671 < z < 1.703 and magnifications in the range Delta m = -0.31 to -1.58 mag, as calculated from lensing models in the literature. Owing to the power of the lensing cluster, the survey had the sensitivity to detect supernovae up to very high redshifts, z similar to 3, albeit for a limited region of space. We present a study of the core-collapse supernova rates for 0.4 < z < 2.9, and find good agreement with previous estimates and predictions from star formation history. During our survey, we also discovered two Type Ia supernovae in A 1689 cluster members, which allowed us to determine the cluster Ia rate to be 0.14(-0.09)(+0.19) SNuB h(2) (SNuB 10(-12) SNe L-circle dot,B(-1) yr(-1)), where the error bars indicate 1 sigma confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10(-0.06)(+0.13) +/- 0.02 in SNuM h(2) (SNuM = 10(-12) SNe M-1 yr(-1)). Furthermore, we explore the optimal future survey for improving the core-collapse supernova rate measurements at z greater than or similar to 2 using gravitational telescopes, and for detections with multiply lensed images, and we find that the planned WFIRST space mission has excellent prospects. Conclusions. Massive clusters can be used as gravitational telescopes to significantly expand the survey range of supernova searches, with important implications for the study of the high-z transient Universe.

Keyword
supernovae: general, gravitational lensing: strong, galaxies: star formation, galaxies: clusters: individual: A 1689, techniques: photometric
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-140360 (URN)10.1051/0004-6361/201628925 (DOI)000385832200100 ()
Available from: 2017-03-31 Created: 2017-03-31 Last updated: 2017-04-26Bibliographically approved
2. iPTF16geu: A multiply imaged, gravitationally lensed type Ia supernova
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2017 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 356, no 6335, 291-295 p.Article in journal (Refereed) Published
Abstract [en]

We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova, iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because the light from the stellar explosion was magnified more than 50 times by the curvature of space around matter in an intervening galaxy. We used high-spatial-resolution observations to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec, smaller than is typical in other studies of extragalactic gravitational lensing. The large magnification and symmetric image configuration imply close alignment between the lines of sight to the supernova and to the lens. The relative magnifications of the four images provide evidence for substructures in the lensing galaxy.

Keyword
supernova, strong lensing
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-141718 (URN)10.1126/science.aal2729 (DOI)000399540100055 ()
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-05-29Bibliographically approved
3. Testing for redshift evolution of Type Ia supernovae using the strongly lensed PS1-10afx at z = 1.4
Open this publication in new window or tab >>Testing for redshift evolution of Type Ia supernovae using the strongly lensed PS1-10afx at z = 1.4
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(English)Manuscript (preprint) (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-141715 (URN)
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-04-26Bibliographically approved
4. Searching for supernovae in the multiply-imaged galaxies behind the gravitational telescope A370
Open this publication in new window or tab >>Searching for supernovae in the multiply-imaged galaxies behind the gravitational telescope A370
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(English)Manuscript (preprint) (Other academic)
Keyword
supernova, strong lensing, galaxy cluster, gravitational telescope
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:su:diva-141717 (URN)
Available from: 2017-04-12 Created: 2017-04-12 Last updated: 2017-04-26Bibliographically approved

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