GCN 44160: GRB 260310A: VLA Multi-frequency Radio Observations

2026-03-30T20:08:21.102Z | rev 0 | event: GRB 260310A
D. A. Perley (LJMU), G. Schroeder (Cornell), and T. Laskar (Utah) report on behalf of a larger collaboration:

The Karl G. Jansky Very Large Array observed the location of the afterglow (Hinds et al., TNS AstroNote 2026-65; Konno et al., GCN 43974) associated with GRB 260310A (Fermi GBM Team, GCN 43951; Hamburg & Meegan, GCN 43975) using all available receivers from S-band to Q-band, providing nearly continuous spectral coverage from 2 to 50 GHz.   Observations were carried out on UT 2026-03-27 between 07:45 and 11:06 UT, approximately 17.2 days after the GRB.

Consistent with previous reports (Rhodes et al., GCN 44005; Giarratana et al., GCN 44045; Ho et al., GCN 44057; Ho et al., GCN 44134) we detect very strong radio emission from the afterglow.  Preliminary flux densities are:

| freq(GHz) |  flux(mJy)     |
|-----------|----------------|
| 3         |  2.90 +/- 0.04 |
| 6         |  7.52 +/- 0.05 |
| 10        | 11.11 +/- 0.11 |
| 15        | 11.73 +/- 0.16 |
| 33        |  9.58 +/- 0.39 |
| 45        |  7.98 +/- 0.27 |

This indicates that the afterglow has brightened at low frequencies since the observations of Giarratana et al. and Rhodes et al. at ~4 days post-GRB, and that the peak of the f_nu spectral energy distribution during our observations was at approximately 15 GHz.

We thank the NRAO for rapidly approving our DDT request for a public multifrequency campaign on this exceptional GRB, and Heidi Medlin for assistance with checking the SBs.   

Further observations are planned.