{
  "bibcode": "2022GCN.33014....1R",
  "body": "A. Rossi (INAF), G. Pugliese (API, Amsterdam university), D. A. Kann \n(Goethe Univ.), B. Schneider (CEA Paris-Saclay), and V. D'Elia (INAF/OAR \nand ASI/SSDC) report on behalf of the Stargate collaboration:\n\nWe performed photometric observations of the afterglow of GRB 221202A \ndetected by the Swift Burst Alert Telescope (BAT) at 20:06:10.56 UT \n(Caputo et al., GCN 33005; De Wet et al., GCN 33007; Beardmore et al., \nGCN 33008;�� Strausbaugh et al., GCN 33009; Evans et al., GCN 33010) with \nthe FORS2 instrument at the ESO VLT-UT1 in the R_Special, I_Bessel and \nz_Gunn filters (in the following RIz). The observation started at \n06:50:29 UT (about 10.73 hours after the BAT detection), and consisted \nof 500 s in R, 800 s in I, and 1320 s in z.\n\nWe detect a source in the XRT error circle in all filters at position \nRA, Dec. (J2000) = 05:08:19.94,-59:49:58.6, astrometrized against Gaia \nDR3 field stars. We measure the following photometry, consistent with \nthe upper limits of MeerLICHT (S. de Wet et al., GCN 33007) and LCOGT \n(R. Strausbaugh et al., GCN 33009):\n\nR = 23.10 +/- 0.05 mag,\nI = 22.68 +/- 0.06 mag,\nz = 22.52 +/- 0.07 mag.\n\nMagnitudes are calibrated against SkyMapper field stars and are in the \nAB system. For the R and I bands we use the Lupton formulas to convert \nthe standard stars to the BVRI photometric system, then convert the \nmeasured magnitudes back to the AB system.\n\nA source at the same position is visible in r'-band images downloaded \nand stacked from the Legacy Imaging Survey, with r' ~ 24.3 mag (AB). \nTherefore, we conclude that the detected source is dominated by the \nafterglow of GRB 221202A and slightly contaminated by the GRB host \ngalaxy. We derive an X-ray to optical slope beta_OX ~ 0.8, therefore the \nafterglow is not dark, just faint.\n\nWe acknowledge the support provided by T. C. Emy and the Paranal staff, \nin particular Ana Escorza, Ricardo Arrue, Marcela Espinoza, and Michael \nAbdul-Masih.",
  "circularId": 33014,
  "createdOn": 1670088539000,
  "email": "andrea.rossi@inaf.it",
  "subject": "GRB 221202A: VLT/FORS2 Afterglow Discovery",
  "submitter": "Andrea Rossi at INAF  <andrea.rossi@inaf.it>",
  "eventId": "GRB 221202A"
}