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ATCA and ASKAP radio detections of ATLAS/ZTF Potential Supernova transient ATLAS21mwi/ZTF21abbcsyb

ATel #17007; Ashna Gulati (U. Sydney), Tara Murphy (U. Sydney), Katie Auchettl (U. Melbourne/UCSC)
on 31 Jan 2025; 08:06 UT
Credential Certification: Tara Murphy (tara.murphy@sydney.edu.au)

Subjects: Radio, Supernovae, Transient

On 15th April 2021, ATLAS21mwi, a potential supernova transient was reported by the ATLAS bot (Tonry et al., 2021) and given the TNS designation AT2021jve (https://www.wis-tns.org/object/2021jve). The transient was identified as a potential supernova in the ZTF data by the ALeRCE Broker System (Carrasco-Davis et al., 2021) on 12th May 2021. Using observations taken as part of the Rapid ASKAP Continuum Survey (RACS; McConnell et al. 2021), we found radio emission arising from this transient approximately six months after initial discovery, with non-detections at lower ASKAP frequencies of 0.888 GHz, before it brightened at 1.65 GHz.

We initiated radio observations using the Australian Telescope Compact Array (ATCA) to understand whether the radio emission is consistent with a supernova or its host galaxies AGN. The radio observation with the ATCA took place on 28 October 2024 at frequencies 2.1, 5.5 and 9.0 GHz, and the source was detected at all three observed frequencies. The ATCA observations give a spectral index of -0.93 +/- 0.05, consistent with synchrotron emission arising from a potential supernova forward shock interacting with the circum-stellar material.

We report the detections and 5-sigma upper limits below:

Date (UTC)TelescopeFrequency (GHz)Flux Density (mJy)
2019-04-27ASKAP0.888< 1.45
2021-01-23ASKAP 1.367 < 0.88
2022-01-14ASKAP 1.655 4.36 +/- 0.38
2022-02-22ASKAP 1.655 4.96 +/- 0.21
2022-03-02ASKAP 1.655 4.30 +/- 0.40
2022-04-19ASKAP 0.888 <0.85
2023-06-12VLA 3.000 <1.44 +/- 0.17
2024-01-07ASKAP 0.943 <2.74 +/- 0.22
2024-10-28ATCA 1.332 1.35 +/- 0.19
2024-10-28ATCA 1.844 1.13 +/- 0.13
2024-10-28ATCA 2.100 1.00 +/- 0.08
2024-10-28ATCA 2.356 1.07 +/- 0.09
2024-10-28ATCA 2.868 0.73 +/- 0.08
2024-10-28ATCA 5.500 0.46 +/- 0.03
2024-10-28ATCA 9.000 0.23 +/- 0.02

We thank CSIRO staff for supporting these observations.