The search for superluminous supernovae with the Dark Energy Camera
Student thesis: Doctoral Thesis
We present the search for Superluminous Supernovae (SLSNe) within the Dark Energy Survey (DES), and using the Dark Energy Camera (DECam) in general. We construct empirical selection criteria for the selection of SLSNe from the first year of DES data followed by visual inspection of candidates. We present DES13S2cmm, the first spectroscopically-confirmed SLSN from DES, as a hydrogen-poor SLSN at a redshift of z = 0.663 ± 0.001. We updated our SLSNe search methodology based on our experiences and knowledge gained from this first season of DES data. In combination with the increase of the spectroscopic follow-up resources in the second year of DES operations, we have found 22 SLSNe candidates, 7 of which where spectroscopically confirmed as SLSNe events in the redshift range of 0.47 ≤ z ≤ 1.5. We present in detail the seven confirmed SLSNe and we draw attention to three SNe as the highlights of our SLSNe quest in DES Y2. Firstly, DES14S2qri was discovered at a redshift of z = 1.5, as themost luminous SN (Mz = −22.90) up to the writing of this thesis. DES14C1rhg was discovered at a redshift of z = 0.47 as the least luminous SLSN-I (Mr = −19.80), a finding that supports the hypothesis of a continuum that fills the gap between the peak brightness of SNe Ic and SLSNe-I. Lastly, DES14X3taz was detected at a redshift of z = 0.6 and is the second ever recorded SLSN to possess a well constrained pre-peak bump, which could be caused by a pre-explosion outburst of the SN. Using the DES Y2 sample of SLSNe we provide a basic calculation of the volumetric SLSNe rate, reporting a value of ∼ 206 events Gpc−3 yr−1 h371. This value is compatible with other estimates in the literature, considering the simplicity of our method. We fit the bolometric light curves of the entire SLSNe sample discovered by DES with two competing models for SLSNe-I - the radioactive decay of 56Ni, and a magnetar - and find that the magnetar is formally a better fit overall. Using the Magnetar model, we investigate possible cor-relations between the model parameters. We discovered moderate correlations between the explosion phase (texp) and the rise-time (τm), and between the rise-time (τm) and the spin-down time (P ). Moreover, we compare the bolometric light-curves of the entire SLSNe sample, without clear evidence of common behaviour, that would point towards a standardization. We find that the short DES observing seasons (∼ 5 months per calendar year) are limiting the discerning between the two models which, at late times (beyond 100 rest frame days), behave significantly differently. We present the Survey Using DECam for Superluminous Supernovae (SUDSS) as a complementary effort to DES SN survey, which operates since April 2014 and aims at obtaining a large and homogeneous sample of SLSNe out to redshift z ∼ 3, by maximizing its observing seasons in collaboration with DES SN survey.
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