TITLE:   GCN CIRCULAR
NUMBER:  33321
SUBJECT: GRB 230204B: ATCA radio detection
DATE:    23/02/14 04:42:11 GMT
FROM:    Tara Murphy at U of Sydney  <tara.murphy@sydney.edu.au>

Ashna Gulati (U. Sydney, CSIRO), James Leung (U. Sydney, CSIRO), David Kaplan (UWM), Tara Murphy (U. Sydney)

We observed GRB 230204B (Serino et al., GCN 33265) with the Australia Telescope Compact Array (ATCA), on 2023 February 8 from 13:00 to 23:00 UT (3.6 days after the MAXI/GSC trigger) at 5.5, 9.0, 16.7, 21.2, 33.0 and 35.0 GHz. In our preliminary analysis, we detect the radio counterpart at 16.7 GHz at a position consistent with the GIT optical counterpart position (Swain et al., GCN 33269).

Radio emission has not been detected within 1’ of the GRB position in previous radio surveys: National Radio Astronomy Observatory VLA Sky Survey (NVSS; Condon et al., 1998), Sydney University Molonglo Sky Survey (SUMSS; Mauch et al., 2003), the Rapid ASKAP Continuum Survey (RACS; McConnell et al., 2020) or the Very Large Array Sky Survey (VLASS; Lacy et al., 2019). We measured a VLASS 5-sigma upper limit of 0.69 mJy at 3GHz.

We report the ATCA detection and 5-sigma upper limits below:

Freq (GHz) |  Flux Density (mJy)
—----------------------------------------
5.5              | <0.56
9.0              | <0.25
16.7            | 0.19 +/- 0.03
21.2            | <0.14
33.0            | <0.12
35.0            | <0.13

Further analysis of this data is ongoing.

We thank CSIRO staff for supporting these observations.

The Australia Telescope Compact Array is part of the Australia Telescope National Facility which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Gomeroi people as the traditional owners of the Observatory site.