{
  "submittedHow": "email",
  "circularId": 44476,
  "subject": "GRB 260421B: radio observation with the VLA",
  "eventId": "GRB 260421B",
  "createdOn": 1777996244521,
  "submitter": "Stefano Giarratana at INAF-OAB <s.giarratana@ira.inaf.it>",
  "body": "S. Giarratana (INAF-OAB), M. Giroletti (INAF-IRA),\nG. Ghirlanda (INAF-OAB), N. Di Lalla (Stanford Univ.),\nN. Omodei (Stanford Univ.), O. S. Salafia (INAF-OAB),\nL. Nava (INAF-OAB)\n\n\nAt 05:08:16 UT on 2026 April 22 (T_mid = 1.07 days post-burst) \nthe Karl G. Jansky VLA observed the field of GRB 260421B\n(Fermi GBM team, GCN 44360, 44382; SVOM mission team, GCN 44362,\nGCN 44389, 44397; Insight-HXMT team, GCN 44401) at central\nfrequencies of 6, 10 and 15 GHz.\n\nThe standard 3C286 was used as bandpass and flux density\ncalibrator, while J1239-1023 was used as phase calibrator.\n\nFrom a preliminary analysis, we do not detect the radio\ncounterpart of GRB 260421B. We derive the following upper\nlimits (UL; 3sigma):\n\n================================================================\nT_mid\tFreq\tUL\tr.m.s.\tBeam\t\tPA\n[days]\t[GHz]\t[uJy]\t[uJy/b]\t[arcsec^2]\t[deg]\n================================================================\n1.07\t6\t24\t8\t0.47x0.28\t11\n1.07\t10\t24\t8\t0.30x0.18\t11\n1.07\t15\t27\t9\t0.20x0.11\t-2\n================================================================\n\nWe would like to thank the staff of the VLA for approving, executing,\nand processing the observations.\n\nThe National Radio Astronomy Observatory is a facility of the National\nScience Foundation operated under cooperative agreement by Associated\nUniversities, Inc.\n\nThese observations were carried out as part of project SF181027,\napproved in the framework of the Fermi - NRAO joint program agreement."
}