Rapidly evolving transients in the Dark Energy Survey

Abstract

We present the results of a search for rapidly evolving transients in the Dark Energy Survey Supernova Programme. These events are characterized by fast light curve evolution (rise to peak in 10 d and exponential decline in 30 d after peak). We discovered 72 events, including 37 transients with a spectroscopic redshift from host galaxy spectral features. The 37 events increase the total number of rapid optical transients by more than factor of two. They are found at a wide range of redshifts (0.05 < z < 1.56) and peak brightnesses (−15.75 > M g > −22.25). The multiband photometry is well fit by a blackbody up to few weeks after peak. The events appear to be hot (T ≈ 10000 − 30000 K) and large (R ≈ 10 14 − 2 · 10 15 cm) at peak, and generally expand and cool in time, though some events show evidence for a receding photosphere with roughly constant temperature. Spectra taken around peak are dominated by a blue featureless continuum consistent with hot, optically thick ejecta. We compare our events with a previously suggested physical scenario involving shock breakout in an optically thick wind surrounding a core-collapse supernova (CCSNe), we conclude that current models for such a scenario might need an additional power source to describe the exponential decline. We find these transients tend to favor star-forming host galaxies, which could be consistent with a core-collapse origin. However, more detailed modeling of the light curves is necessary to determine their physical origin.

Observational properties of extreme supernovae

“…Due to the unusual observational properties observed in such transients, a wide range of possibilities has been suggested to explain their behaviour. The PS1 and DES samples showed blue, continuum dominated, spectra consistent with what observed for transients powered by a shock-breakout or recombination in an extended envelope [8] that might be due to an optically thick, low mass circumstellar wind surrounding a core-collapse SN [9]. Such an explanation is also the most widely formation of a magnetar in a binary neutron star merger (ref.…”

“…The peak magnitudes of FBOTs span from the fainter end of core-collapse SNe up to luminosities comparable to those of SLSNe without any significant trend between peak luminosity and evolution [7]. Their rise time is faster than the decline and the redder the band, the longer is the exponential decline timescale [8,9]. The post-peak decline timescales observed in the PS1 and DES samples cover a wide range, which is difficult to explain with a single value for an exponential decline, or in general with a single scenario or powering mechanism [9].…”

“…1), which is below the lines representing the maximum possible luminosity from a standard SN explosion. Some of these transients overall evolution is usually not as fast as the events presented in the Pan-STARRS (or PS1), the Subaru Hyper Suprime-Cam Transient Survey and the Dark Energy Survey (DES) samples [8,9,91], which in literature are becoming more often referred to as Fast Blue Optical Transients (FBOTs). Moreover, the transients of such samples, as well as the nearby event AT2018cow at 60 Mpc[101, 102, 103, 104, 105], show timescales and spectroscopic evolution inconsistent with any standard scenario or model able to reproduce the observables (or some of them) of the objects mentioned above.…”

“…FBOTs are usually characterised by a rapid light-curve rise to the peak (≲10 days from the last nondetection) and an exponential decline in 30 days after peak [9] (Fig. 4, left panel), or a time above half-maximum luminosity (t1/2) of less than 12 days [8] (Fig.…”

LSQ13ddu: a rapidly evolving stripped-envelope supernova with early circumstellar interaction signatures

“…In recent years transient surveys such as the Asteroid Terrestrial-impact Last Alert System (ATLAS; Tonry et al 2018), the La-Silla QUEST survey (LSQ; Baltay et al 2013), the All-Sky Automated Survey for Supernovae (ASAS-SN; Shappee et al 2014), the Dark Energy Survey (DES; Pursiainen et al 2018), and the Zwicky Transient Facility (ZTF; Bellm et al 2019) have used high-cadence observations (repeat visits every ∼1 -3 d) to reveal and study new classes of luminous and rapidly evolving transients (Drout et al 2014;Arcavi et al 2016). Numerous other objects showing exotic and unusual behaviour have been observed such as iPTF16asu (Whitesides et al 2017) and AT 2018cow (Prentice et al 2018b), with these transients presenting challenges to existing explosion models and progenitor scenarios.…”