Rapidly Evolving Transients from the Hyper Suprime-Cam SSP Transient Survey

Abstract

Rapidly evolving transients form a new class of transients which show shorter timescales of the light curves than those of typical core-collapse and thermonuclear supernovae. We performed a systematic search for rapidly evolving transients using the deep data taken with the Hyper Suprime-Cam Subaru Strategic Program Transient Survey. By measuring the timescales of the light curves of 1824 transients, we identified 5 rapidly evolving transients. Our samples are found in a wide range of redshifts (0.3 ≤ z ≤ 1.5) and peak absolute magnitudes (−17 ≥ M i ≥ −20). The properties of the light curves are similar to those of the previously discovered rapidly evolving transients. They show a relatively blue spectral energy distribution, with the best-fit blackbody of 8,000 -18,000 K. We show that some of the transients require power sources other than the radioactive decays of 56 Ni because of their high peak luminosities and short timescales. The host galaxies of all the samples are star-forming galaxies, suggesting a massive star origin for the rapidly evolving transients. The event rate is roughly estimated to be ∼4,000 events yr −1 Gpc −3 , which is about 1 % of core-collapse supernovae.

A systematic study on the rise time-peak luminosity relation for bright optical transients powered by wind shock breakout

“…Among them, the CSM interaction has long been considered as a major energy source for luminous type IIn SNe (Schlegel 1990;Filippenko 1997;Smith 2017;Blinnikov 2017), which show some narrow line features in their spectra and thus imply the presence of slowly moving materials ahead of the SN ejecta. The interaction-powered emission has also been paid great attention since the modern transient surveys, e.g., Palomar Transient Factory (PTF: Law et al 2009), ASAS-SN (Kochanek et al 2017), Pan-STARRS (Chambers et al 2016), and Subaru Hyper Suprime-Cam Subaru Strategic Program (Miyazaki et al 2018;Aihara et al 2018;Yasuda et al 2019), have discovered optical transients with short rising and declining timescales (e.g., Ofek et al 2010;Drout et al 2014;Arcavi et al 2016;Tanaka et al 2016;Pursiainen et al 2018;Tominaga et al 2019;Tampo et al 2020). In addition to ground-based telescopes, the recent advance in space-based monitoring surveys, such as the Kepler mission (Borucki et al 2010;Koch et al 2010;Howell et al 2014), also realized the early detection and subsequent follow-up observations of intriguing optical transients potentially explained by the interaction-powered emission, e.g., KSN 2015K (Rest et al 2018).…”