1. High-redshift supernova rates measured with the gravitational telescope A 1689Tanja Petrushevska, R. Amanullah, Ariel Goobar, S. Fabbro, Joel Johansson, Tor Kjellsson, Chris Lidman, K. Paech, Johan Richard, H. Dahle, Raphael Ferretti, J.P. Kneib, M. Limousin, Jakob Nordin, V. Stanishev, 2016, original scientific article Abstract: 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 ∆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 ∼ 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+0.19 −0.09 ± 0.01 SNuB h 2 (SNuB ≡ 10−12 SNe L −1 ,B yr−1), where the error bars indicate 1σ confidence intervals, statistical and systematic, respectively. The cluster rate normalized by the stellar mass is 0.10+0.13 −0.06 ± 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 & 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.
Keywords: supernovae: general – gravitational lensing: strong – galaxies: star formation – galaxies: clusters: individual: A 1689 –
techniques: photometric
Published in RUNG: 23.01.2018; Views: 4393; Downloads: 0
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2. Supernova spectra below strong circumstellar interactionGiorgos Leloudas, E.Y. Hsiao, Joel Johansson, Keichi Maeda, T.J. Moriya, Jakob Nordin, Tanja Petrushevska, J. M. Silverman, Jesper Sollerman, M.D. Stritzinger, Francesco Taddia, D. Xu, 2015, original scientific article Abstract: We construct spectra of supernovae (SNe) interacting strongly with a circumstellar medium (CSM) by adding SN templates, a blackbody
continuum, and an emission-line spectrum. In a Monte Carlo simulation we vary a large number of parameters, such as the SN
type, brightness and phase, the strength of the CSM interaction, the extinction, and the signal to noise ratio (S/N) of the observed
spectrum. We generate more than 800 spectra, distribute them to ten different human classifiers, and study how the different simulation
parameters affect the appearance of the spectra and their classification. The SNe IIn showing some structure over the continuum were
characterized as “SNe IInS” to allow for a better quantification. We demonstrate that the flux ratio of the underlying SN to the
continuum fV is the single most important parameter determining whether a spectrum can be classified correctly. Other parameters,
such as extinction, S/N, and the width and strength of the emission lines, do not play a significant role. Thermonuclear SNe get
progressively classified as Ia-CSM, IInS, and IIn as fV decreases. The transition between Ia-CSM and IInS occurs at fV ∼ 0.2−0.3. It
is therefore possible to determine that SNe Ia-CSM are found at the (un-extincted) magnitude range −19.5 > M > −21.6, in very good
agreement with observations, and that the faintest SN IIn that can hide a SN Ia has M = −20.1. The literature sample of SNe Ia-CSM
shows an association with 91T-like SNe Ia. Our experiment does not support that this association can be attributed to a luminosity bias
(91T-like being brighter than normal events). We therefore conclude that this association has real physical origins and we propose that
91T-like explosions result from single degenerate progenitors that are responsible for the CSM. Despite the spectroscopic similarities
between SNe Ibc and SNe Ia, the number of misclassifications between these types was very small in our simulation and mostly at low
S/N. Combined with the SN luminosity function needed to reproduce the observed SN Ia-CSM luminosities, it is unlikely that SNe Ibc
constitute an important contaminant within this sample. We show how Type II spectra transition to IIn and how the Hα profiles vary
with fV . SNe IIn fainter than M = −17.2 are unable to mask SNe IIP brighter than M = −15. A more advanced simulation, including
radiative transfer, shows that our simplified model is a good first order approximation. The spectra obtained are in good agreement
with real data.
Keywords: supernovae
Published in RUNG: 22.01.2018; Views: 4227; Downloads: 0
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