Mass-loss rate constraint on the Type Ia SN 2021aefx from ATCA radio observations

ATel #15077; E. Kundu (Michigan State University), P. Lundqvist (Stockholm University), S. D. Ryder (Macquarie University), M. Perez-Torres (IAA-CSIC, Granada), C.-I. Bjornsson (Stockholm University), C. Fransson (Stockholm University), M. D. Filipovic (Western Sydney University), D. Venkattu (Stockholm University)
on 30 Nov 2021; 04:00 UT
Credential Certification: Esha Kundu (kunduesh@msu.edu)

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We report the non-detection at radio wavelengths of the Type Ia SN 2021aefx, discovered on 2021-11-11 12:30:43.776 UT at the position RA(J2000.0)= 04:19:53.320, DEC(J2000.0)=-54:56:52.60 (TNS Astronomical Transient Report No. 129095). SN 2021aefx occurred in the galaxy NGC 1566 (z=0.005; D=14.9 Mpc from arXiv:2009.04090), and was confirmed to be a Type Ia event 2 days later (TNSCR3899). We observed SN 2021aefx on 2021-11-13 between UT 14:30-17:30 and 2021-11-19 from UT 13:00 to 17:00 using the Australia Telescope Compact Array (ATCA). In the first epoch, we observed the SN at central frequencies of 5.5 GHz, 9 GHz and 18 GHz using a bandwidth of 2 GHz, while for the second epoch only central frequencies of 5.5 GHz and 9 GHz were used. We found no evidence of radio emission at the expected location of SN 2021aefx in either epoch. The 3-sigma upper limits on the flux density were 0.07 mJy (5.5 GHz), 0.06 mJy (9 GHz), and 0.05 mJy (18 GHz) at the first epoch; and 0.04 mJy (5.5 GHz) and 0.03 mJy (9 GHz) at the second epoch. Adopting the host galaxy distance as 14.9 Mpc, the 3-sigma limit of 0.07 mJy at 5.5 GHz corresponds to an upper limit on the monochromatic luminosity of 1.86e25 erg/s. For our standard model with a presupernova wind speed of 100 km/s (see ATels #11324, #12411, #14325) the above limit to the radio luminosity corresponds to an upper limit of 1.6e-8 solar masses per year for the mass-loss rate, assuming that SN 2021aefx exploded on Nov 7 UT, i.e., days before our first observation. The upper limit to the mass-loss rate of SN 2021aefx is among the most stringent upper limits found for Type Ia SNe (Lundqvist et al. 2020 ApJ 890 159), illustrating the importance of probing the radio emission from Type Ia SNe within a radius of about 20 Mpc. We would like to extend our thanks to the ATCA staff for enabling these observations. The ATCA is part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site.