VLASS constraints on the radio afterglow of the GRB afterglow/hypernova candidate SRGe J195057.5+672122
ATel #14059; B. Marcote (JIVE), M. Giroletti (INAF), G. Migliori (INAF), S. Giarratana (U. Bologna)
on 1 Oct 2020; 17:18 UT
Credential Certification: Benito Marcote (marcote@jive.eu)
Subjects: Radio, Gamma-Ray Burst, Transient
We report the first constraints on the putative radio emission of SRGe J195057.5+672122, reported as a possible gamma-ray burst (GRB) afterglow/hypernova (Sazonov et al. ATel #13987) with a fading optical emission (Perley, ATel #13989; Zaznobin et al. ATel #13990).
We have analyzed the available data from the Karl G. Jansky Very Large Array Sky Survey (VLASS) taken on 23 August 2020 at a central frequency of 3.0 GHz (with a total bandwidth of 2 GHz). This epoch took place approximately a couple of months after the estimated time for the GRB (May-June 2020; see ATel #13987).
No significant emission is reported above a 3-sigma level of 0.45 mJy/beam, where the resulting synthesized beam is 3.2" x 2.3" (and position angle of -54.5 deg). For reference, a previous VLASS epoch on 8 September 2017 (years before the putative GRB) also shows no significant radio emission at a 3-sigma upper-limit of 0.45 mJy/beam. At the estimated distance of z ~ 0.06 (ATel #13987), the obtained value implies an upper-limit on the radio luminosity of ~ 1.2 x 10^38 erg/s, using standard cosmological parameters.
We note that GRB/hypernova classified events like GRB 980425 or GRB 030329 reached the peak of the radio emission at similar frequencies around 30-40 and 60 days post burst, respectively. Therefore, the reported observation likely took place around or right after the expected maximum of the radio emission.
Additional, more sensitive, radio observations with the VLA will be conducted to search for the expected radio afterglow.
