The HSC-SSP Transient Survey: Implications from Early Photometry and Rise Time of Normal Type Ia Supernovae

Abstract

With a booming number of Type Ia supernovae (SNe Ia) discovered within a few days of their explosions, a fraction of SNe Ia that show luminosity excess in the early phase (early-excess SNe Ia) have been confirmed. In this article, we report early-phase observations of seven photometrically normal SNe Ia (six early detections and one deep non-detection limit) at the COSMOS field through a half-year transient survey as a part of the Hyper Suprime-Cam Subaru Strategic Program (HSC SSP). In particular, a blue light-curve excess was discovered for HSC17bmhk, a normal SN Ia with rise time longer than 18.8 days, during the first four days after the discovery. The blue early excess in optical wavelength can be explained not only by interactions with a non-degenerate companion or surrounding dense circumstellar matter but also radiation powered by radioactive decays of 56 Ni at the surface of the SN ejecta. Given the growing evidence of the early-excess discoveries in normal SNe Ia that have longer rise times than the average and a similarity in the nature of the blue excess to a luminous SN Ia subclass, we infer that early excess discovered in HSC17bmhk and other normal SNe Ia are most likely attributed to radioactive 56 Ni decay at the surface of the SN ejecta. In order to successfully identify normal SNe Ia with early excess similar to that of HSC17bmhk, early UV photometries or high-cadence blue-band surveys are necessary.

The detection efficiency of Type Ia supernovae from the Zwicky Transient Facility: limits on the intrinsic rate of early flux excesses

“…They also note however that the fraction of SNe Ia with an excess is highly dependent on the SN subclass. Finally, Jiang et al (2020) present a handful of young SNe Ia observed as part of the HSC-SSP survey and estimate an early excess rate of ∼14% based on power-law fits to the early light curve.…”

Optical and Near-Infrared Observations of the Nearby Type Ia Supernova 2017cbv

“…Excess emission in the early light curve has been reported in a number of SNe Ia (Cao et al 2015;Marion et al 2016;Hosseinzadeh et al 2017a;Jiang et al 2018;Dimitriadis et al 2019a;Shappee et al 2019;Li et al 2019b). Al-ternatively, these early light curve features may be associated with mixing of radioactive 56 Ni (Piro & Morozova 2016;Miller et al 2018;Magee et al 2018;Jiang et al 2020;, He-shell detonation (Jiang et al 2017;Maeda et al 2018;Polin et al 2019;Siebert et al 2020), or circumstellar material interaction in DD scenario (Levanon & Soker 2017. Meanwhile, other studies have searched for narrow Hα/He emission lines in nebular phase spectra as a characteristic signature of the SD scenario (Marietta et al 2000;Mattila et al 2005;Pan et al 2010;Leonard 2007;Pan et al 2012;Liu et al 2012Liu et al , 2013Lundqvist et al 2013Lundqvist et al , 2015Shappee et al 2018;Graham et al 2015;Maguire et al 2016;Botyánszki et al 2018;Sand et al 2018Sand et al , 2019Shappee et al 2018;Dimitriadis et al 2019b;Holmbo et al 2019;Tucker et al 2019).…”

Prospects of Searching for Type Ia Supernovae with 2.5-m Wide Field Survey Telescope

“…The Equation of State Supernova Cosmology Experiment program found about 200 SNe Ia with redshifts from 0.1 to 0.8 using the 4-meter CTIO Blanco telescope during its 2002-2008 running [30,31]. With the Hubble Space Telescope and the Subaru Hyper Suprime-Cam, the redshifts of discovered SNe Ia have been up to above 1.5 [10,[32][33][34][35]. On the other hand, several supernova surveys are designed to catch the nearby supernovae to investigate their physical nature.…”