{
  "bibcode": "2017GCN.20510....1S",
  "body": "B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), A.P. Beardmore (U.\nLeicester), S.L. Gibson (U. Leicester), A. D'Ai (INAF-IASFPA), A.\nMelandri (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Cholden-Brown (PSU),\nP.A. Evans (U. Leicester) and A.A. Breeveld (UCL-MSSL) report on behalf\nof the Swift team:\n\nSwift-XRT has performed follow-up observations of the optical transient\nreported by Lipunov et al. (GCN Circ. 20502) as a possible candidate\nafterglow of the Fermi/GBM-detected burst GRB 170121B (Hamburg et al.\nGCN Circ. 20505), collecting 4.5 ks of Photon Counting (PC) mode data\nbetween T0+124.0 ks and T0+147.4 ks. \n\nNo X-ray sources have been detected at the position of the optical\ntransient reported by Lipunov et al. (GCN Circ. 20502). \n\nAn uncatalogued X-ray source is detected within the XRT field of view\nat the position RA, Dec 72.6361, -9.2424 which is equivalent to:\n   RA(J2000)  = 04h 50m 32.66s\n   Dec(J2000) = -09d 14' 32.5\"\nwith an uncertainty of 2.7 arcseconds (radius, 90% containment). The\nsource has a 0.3-10 keV count rate of about 9e-3 ct/sec. We cannot\ndetermine fading at this time.\n\nThe 3-sigma upper limit in the field ranges from ~2e-3 to ~3e-3 ct\ns^-1, corresponding to a 0.3-10 keV observed flux of 6.5e-14 to 1.0e-13\nerg cm^-2 s^-1 (assuming a typical GRB spectrum).\n\nThe results of the XRT-team automatic analysis of the XRT observations,\nincluding a position specific upper limit calculator, are available at\nhttp://www.swift.ac.uk/ToO_GRBs/00020729.\n\n\nThe Swift/UVOT began settled observations 124 ks after the trigger\n(Hamburg et al, GCN Circ. 20505). Summing up the early white data at\nthe position of the OT found by Lipunov et al. (GCN Circ. 20502) we do\nnot find any source to an upper limit of 22.2 mags in 3430s.\nAt the position of the new uncatalogued XRT source described above we\ndo see a source already listed in the USNO-B1.0 catalogue and it is not\nfading.\n\n\nThis circular is an official product of the Swift team.",
  "circularId": 20510,
  "createdOn": 1485183219000,
  "email": "paolo.davanzo@brera.inaf.it",
  "subject": "GRB 170121B: Swift-XRT and UVOT observations",
  "submitter": "Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>",
  "eventId": "GRB 170121B"
}