{
  "createdOn": 1779196642540,
  "bibcode": "2026GCN.44665....1G",
  "eventId": "GRB 260421B",
  "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\nAt 01:30:46 UT on 2026 April 24 (T_mid = 2.92 days post-burst) \nand at 01:38:23 UT on 2026 April 30 (T_mid = 8.92 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, an unresolved radio source\nis detected at 8.92 days post-burst at a position (J2000):\n\nRA: 12:40:00.478 +- 0.002\nDec: -17:44:24.70 +- 0.03\n\nconsistent with the X-ray (SVOM mission team, GCN 44362;\nEinstein Probe team, GCN 44387) and optical (He et al., GCN 44363;\nSánchez Álvarez et al., GCN 44364; SVOM mission team, GCN 44365,\n44377; Wu et al., GCN 44366; Pérez-Fournon et al., GCN 44383;\nGRANDMA/Kilonova-Catcher collaboration, GCN 44402) position\nof the transient.\n\nThe preliminary analysis yields the following results:\n\n================================================================\nT_mid\tFreq\tPeak\tr.m.s.\tBeam\t\tPA\n[days]\t[GHz]\t[uJy/b]\t[uJy/b]\t[arcsec^2]\t[deg]\n================================================================\n2.92\t6\t-\t8\t0.72x0.28\t-38\n2.92\t10\t-\t9\t0.50x0.19\t-43\n2.92\t15\t-\t12\t0.41x0.11\t-43\n8.92\t6\t52\t8\t0.58x0.27\t-33\n8.92\t10\t81\t9\t0.40x0.21\t-38\n8.92\t15\t137\t9\t0.32x0.12\t-38\n================================================================\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.",
  "circularId": 44665,
  "subject": "GRB 260421B: radio detection with the VLA",
  "submitter": "Stefano Giarratana at INAF-OAB <s.giarratana@ira.inaf.it>",
  "submittedHow": "email"
}