Constraints on the rate of supernovae lasting for more than a year from Subaru/Hyper Suprime-Cam

Kavli Affiliate: Naoki Yasuda

| First 5 Authors: Takashi J. Moriya, Ji-an Jiang, Naoki Yasuda, Mitsuru Kokubo, Kojiro Kawana

| Summary:

Some supernovae such as pair-instability supernovae are predicted to have the
duration of more than a year in the observer frame. To constrain the rates of
supernovae lasting for more than a year, we conducted a long-term deep
transient survey using Hyper Suprime-Cam (HSC) on the 8.2m Subaru telescope.
HSC is a wide-field (a 1.75 deg2 field-of-view) camera and it can efficiently
conduct transient surveys. We observed the same 1.75 deg2 field repeatedly
using the g, r, i, and z band filters with the typical depth of 26 mag for 4
seasons (from late 2016 to early 2020). Using these data, we searched for
transients lasting for more than a year. Two supernovae were detected in 2
continuous seasons, one supernova was detected in 3 continuous seasons, but no
transients lasted for all 4 seasons searched. The discovery rate of supernovae
lasting for more than a year with the typical limiting magnitudes of 26 mag is
constrained to be 1.4^{+1.3}_{-0.7}(stat.)^{+0.2}_{-0.3}(sys.) events deg-2
yr-1. All the long-lasting supernovae we found are likely Type IIn supernovae
and our results indicate that about 40% of Type IIn supernovae have
long-lasting light curves. No plausible pair-instability supernova candidates
lasting for more than a year are discovered. By comparing the survey results
and survey simulations, we constrain the luminous pair-instability supernova
rate up to z ~ 3 should be of the order of 100 Gpc-3 yr-1 at most, which is
0.01 – 0.1 per cent of the core-collapse supernova rate.

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