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

Abstract

We present multi-wavelength 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 year span. Using this sample, we constrain the rates of faint Iax (Mr ≳ −16) events within 60 Mpc at $12^{+14}_{-8}\%$ of the SN Ia rate. The overall Iax rate, at $15^{+17}_{-9}\%$ 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 $0.9^{+1.1}_{-0.5}\%$ of the Ia rate (a 2σ upper limit of approximately 3%). 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 $1-18\%$ of the SN Ia rate for this channel, consistent with our rate estimates.

A New Study on a Type Iax Stellar Remnant and its Probable Association with SN 1181

“…If the extended halo-like feature in the AKARI 90 μm data (radius 128″ ± 5″) is the farthest extent of the nebula, then the ejecta velocity would be ∼1700 km s −1 not much different from that of the shocked emission. Both values are consistent with the general decline of ejecta velocities more than 100 days post-eruption in Type Iax SNe (e.g., Kawabata et al 2018;Srivastav et al 2022).…”

Discovery of an Exceptional Optical Nebulosity in the Suspected Galactic SN Iax Remnant Pa 30 Linked to the Historical Guest Star of 1181 CE

“…Finally, the peak visual magnitude of SN 1181 has been estimated to be between +1.0 and −0.5 (Ritter et al 2021) or 0.0 and -1.4 (Schaefer 2022) which, assuming an A V ∼ 2.4-2.9 mag (Ritter et al 2021;Lykou et al 2022), implies M V values between −12 and −16. Such numbers indicate a subluminous SN event, consistent with the picture of a SN 1181 being a subluminous type Iax event which shows similar values (Jha 2017;Srivastav et al 2022). The presence of a hot central stellar remnant completes the picture of Pa 30 as a young SNR from a double-degenerate merger in a SN Iax event as some have proposed (Schwab et al 2016;Kashiyama et al 2019;Oskinova et al 2020).…”

Discovery of an Exceptional Optical Nebulosity in the Suspected Galactic SN Iax Remnant Pa 30 Linked to the Historical Guest Star of 1181 CE

“…Finally, the peak visual magnitude of SN 1181 has been estimated to be between +1.0 and −0.5 (Ritter et al 2021) or 0.0 and −1.4 (Schaefer 2023) which, assuming an A V ∼2.4-2.9 mag (Ritter et al 2021;Lykou et al 2023), implies M V values between −12 and −16. Such numbers indicate a subluminous SN event, consistent with the picture of SN 1181 being a subluminous type Iax event, which shows similar values (Jha 2017;Srivastav et al 2022). The presence of a hot central stellar remnant completes the picture of Pa 30 as a young SNR from a double-degenerate merger in a, SN Iax event as some have proposed (Kashiyama et al 2019;Oskinova et al 2020).…”

“…Because of its unusual central star, Pa 30 has been suggested as being an SNR arising from a double-degenerate merger leading to an SN Ia known as an SN Iax event (Gvaramadze et al 2019;Kashiyama et al 2019;Oskinova et al 2020;Ritter et al 2021;Lykou et al 2023). SNe Iax are characterized as subluminous SNe, the faintest of which have M V, peak = −13 to −16 (Srivastav et al 2022) However, Pa 30ʼs highly spherical morphology is in sharp contrast to the strongly asymmetric SN Iax ejecta in some models (Kashyap et al 2018).…”