SN 2020kyg and the rates of faint Iax supernovae from ATLAS

Shubham Srivastav, S J Smartt, M E Huber, K C Chambers, C R Angus, T-W Chen, F P Callan, J H Gillanders, O R McBrien, S A Sim, M Fulton, J Hjorth, K W Smith, D R Young, K Auchettl, J P Anderson, G Pignata, T J L de Boer, C-C Lin, E A Magnier

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We present multiwavelength follow-up observations of the ATLAS discovered faint Iax supernova SN 2020kyg that peaked at an absolute magnitude of Mg ≈ −14.9 ± 0.2, making it another member of the faint Iax supernova population. The bolometric light curve requires only ≈7 × 10−3 M⊙ of radioactive 56Ni, with an ejected mass of Mej ∼ 0.4 M⊙ and a low kinetic energy of E ≈ 0.05 ± 0.02 × 1051 erg. We construct a homogeneous volume-limited sample of 902 transients observed by ATLAS within 100 Mpc during a 3.5 yr span. Using this sample, we constrain the rates of faint Iax (Mr ≳ −16) events within 60 Mpc at 12+14−8 per cent of the SN Ia rate. The overall Iax rate, at 15+17−9 per cent of the Ia rate, is dominated by the low-luminosity events, with luminous SNe Iax (Mr ≲ −17.5) like 2002cx and 2005hk, accounting for only 0.9+1.1−0.5 per cent of the Ia rate (a 2σ upper limit of approximately 3 per cent). We favour the hybrid CONe WD + He star progenitor channel involving a failed deflagration of a near Chandrasekhar mass white dwarf, expected to leave a bound remnant and a surviving secondary companion, as a candidate explanation for faint Iax explosions. This scenario requires short delay times, consistent with the observed environments of SNe Iax. Furthermore, binary population synthesis calculations have suggested rates of 1−18 per cent of the SN Ia rate for this channel, consistent with our rate estimates.
Original languageEnglish
Pages (from-to)2708–2731
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date28 Jan 2022
Publication statusPublished - Apr 2022


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