A Rapidly Declining Transient Discovered with the Subaru/Hyper Suprime-Cam

Abstract

We perform a high-cadence transient survey with Subaru Hyper Suprime-Cam (HSC), which we call the Subaru HSC survey Optimized for Optical Transients (SHOOT). We conduct HSC imaging observations with time intervals of about one hour on two successive nights, and spectroscopic and photometric follow-up observations. A rapidly declining blue transient SHOOT14di at z = 0.4229 is found in observations on two successive nights with an image subtraction technique. The rate of brightness change is +1.28 +0.40 −0.27 mag day −1 (+1.83 +0.57 −0.39 mag day −1 ) in the observer (rest) frame and the rest-frame color between 3400 and 4400Å is MThe nature of the object is investigated by comparing its peak luminosity, decline rate, and color with those of transients and variables previously observed, and those of theoretical models. None of the transients or variables share the same properties as SHOOT14di. Comparisons with theoretical models demonstrate that, while the emission from the cooling envelope of a Type IIb supernova shows a slower decline rate than SHOOT14di, and the explosion of a red supergiant star with a dense circumstellar wind shows a redder color than SHOOT14di, the shock breakout at the stellar surface of the explosion of a 25M ⊙ red supergiant star with a small explosion energy of ≤ 0.4 × 10 51 erg reproduces the multicolor light curve of SHOOT14di. This discovery shows that a high-cadence, multicolor optical transient survey at intervals of about one hour, and continuous and immediate follow-up observations, is important for studies of normal core-collapse supernovae at high redshifts.

MUSSES2020J: The Earliest Discovery of a Fast Blue Ultraluminous Transient at Redshift 1.063

“…Since 2014, a series of transient surveys aiming to discover supernovae (SNe) within a few days of their explosions have been carried out through Subaru open-use programs (Tanaka et al 2016;Jiang et al 2017;Tominaga et al 2019). The "MUlti-band Subaru Survey for Early-phase Supernovae" (MUSSES) is a representative project which is designed to catch the first light of SNe with Subaru/HSC.…”

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).…”

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

“…Their light curves evolve much faster than the normal SNe. Until today, a considerable number of rapidly evolving transients have been identified, including SN 2002bj (Poznanski et al 2010), SN 2005ek (Drout et al 2013), SN 2010X (Kasliwal et al 2010), iPTF 16asu from Palomor Transient Factory (Whitesides et al 2017), KSN2015K from Kepler mission (Rest et al 2018), SN 2017czd (Nakaoka et al 2019), AT2018cow (Prentice et al 2018;Perley et al 2019), SN 2018bgv (Lunnan et al 2019), SN 2018gep (Ho et al 2019), SN 2019 bkc (Chen et al 2019;Prentice et al 2019), SN 2018kzr (McBrien et al 2019) and SHOOT14di (Tominaga et al 2019). Also, a few systematic searches have been performed and 14 and 72 rapidly evolving transients have been identified with PS1 (Drout et al 2014) and Dark Energy Survey (DES, Pursiainen et al 2018), respectively.…”