TITLE: GCN CIRCULAR NUMBER: 41038 SUBJECT: GRB 250704B / EP250704a: VLA radio detection DATE: 25/07/08 17:46:51 GMT FROM: Genevieve Schroeder at Cornell University genevieveschroeder@u.northwestern.edu
G. Schroeder (Cornell), J. Rastinejad, W. Fong (Northwestern), T. Laskar (Utah) report:
We observed the location of the short-duration GRB 250704B/EP 250704A (Wang et al., GCN 40940; Li et al., GCNs 40941, 40956, Frederiks et al., GCN 40972; Wang et al., GCN 40978; Shimizu et al., GCN 41025) with the Karl G. Jansky Very Large Array (VLA) in C configuration under program 25A-063 (PI Schroeder) at a mid time of 2025 July 8 at 09:57 UT (4.1 days post-burst) for 1.25 hours at a mean frequency of 6 GHz.
In preliminary analysis, we detect a 20-sigma radio source with a flux density of ~150 microJy at the position:
RA(J2000) = 20:03:29.511 Dec(J2000) = +12:01:23.31
with an uncertainty of ~0.2" in each coordinate. This position is consistent with the X-ray position (Li et al., GCNs 40941, 40956; Evans et al. GCN 40951, Salvaggio et al. GCN 40987) and optical position (Schneider et al., GCN 40942). At z=0.661 (An et al. GCN 40966), this corresponds to a rest-frame luminosity of ~ 2e30erg/s/Hz, on the bright end of typical short-duration Gamma-ray burst radio afterglow luminosities at a similar rest-frame time (e.g., Laskar et al. 2022). Further observations are planned to assess the variability of the radio source and its connection to GRB 250704B and EP250704A.
We thank the VLA staff for quickly approving and executing these observations.
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