TITLE: GCN CIRCULAR NUMBER: 35642 SUBJECT: GRB 240122A: ATCA detection of radio counterpart DATE: 24/01/27 06:27:28 GMT FROM: Gemma Anderson at Curtin U gemma.anderson@curtin.edu.au

G. E. Anderson (Curtin), A. Gulati (USyd), L. Rhodes (Oxford), J. K. Leung (UofT/HUJI), A. J. van der Horst (GWU), S. Chastain (UNM) on behalf of the PanRadio GRB collaboration

The Australia Telescope Compact Array (ATCA) observed the MAXI-detected long GRB 240122A (Negoro et al., GCN 35593) at the GOTO (Kumar et al., GCN 35596) and Swift-XRT localisation (Ambrosi et al., GCN 35600) as part of the Large ATCA "PanRadio GRB" follow-up program C3542 (PI. Anderson).

The observation took place on 2024-01-24 at 12:00 UT for 2.5 hours at 5.5 and 9 GHz. We detected a candidate radio afterglow at 9 GHz consistent with the GOTO and XRT position with a preliminary flux density of ~160 microJy with a RMS sensitivity of 20 microJy, and obtained a 3 sigma upper limit of 135 microJy at 5.5 GHz.

Further observations are planned.

We thank the CSIRO Space and Astronomy staff for supporting these observations. We acknowledge the Gomeroi people as the traditional owners of the Observatory site. The Australia Telescope Compact Array is part of the Australia Telescope National Facility (https://ror.org/05qajvd42) which is funded by the Australian Government for operation as a National Facility managed by CSIRO.

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