Kavli Affiliate: Naoki Yasuda
| First 5 Authors: Seiji Toshikage, Masaomi Tanaka, Naoki Yasuda, Takashi J. Moriya, Ichiro Takahashi
| Summary:
Recent high-cadence transient surveys have discovered rapid transients whose
light curve timescales are shorter than those of typical supernovae. In this
paper, we present a systematic search for rapid transients at medium-high
redshifts among 3381 supernova candidates obtained from the Subaru HSC-SSP
transient survey. We developed a machine learning classifier to classify the
supernova candidates into four types (Type Ia, Ibc, II supernovae, and rapid
transients) based on the features derived from the light curves. By applying
this classifier to the 3381 supernova candidates and by further applying the
quality cut, we selected 14 rapid transient samples. They are located at a wide
range of redshifts ($0.34 leq z leq 1.85$) and show a wide range of the peak
absolute magnitude ($-17 geq M geq -22$). The event rate of the rapid
transients is estimated to be $sim 6times10^3~rm{events~yr^{-1}~Gpc^{-3}}$
at $z sim 0.74$, which corresponds to about $2$ $%$ of the event rate of
normal core-collapse supernovae at the similar redshift. Based on the
luminosity and color evolution, we selected two candidates of Type Ibn
supernovae at $zsim0.75$. The event rate of Type Ibn SN candidates is more
than 1 $%$ of Type Ib SN rate at the same redshift, suggesting that this
fraction of massive stars at this redshift range eruptively ejects their
He-rich envelope just before the explosions. Also, two objects at $z=1.37$ and
1.85 show high luminosities comparable to superluminous supernovae. Their event
rate is about 10-25 $%$ of superluminous supernovae at $zsim 2$.
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