{
  "bibcode": "2023GCN.33429....1B",
  "body": "D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U. Leicester),\nK.L. Page (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti\n(INAF-OAB), A. D'Ai (INAF-IASFPA), S. Dichiara (PSU) and P.A. Evans (U.\nLeicester) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/GBM-detected burst GRB 230307A (Dalessi et al. GCN Circ. 33407)\nin a series of observations tiled on the sky. The total exposure time\nis 8.6 ks, distributed over 32 tiles; the maximum exposure at a single\nsky location was 1.6 ks. The data were collected between T0+76.4 ks and\nT0+100.9 ks, and are entirely in Photon Counting (PC) mode. \n\nTwo X-ray sources have been detected within the improved IPN error box\n(Kozyrev et al., GCN Circ. 33425), that has been fully covered by\nSwift/XRT observations.\n\n\nSource 2:\n   RA (J2000): 04h 03m 26.24s = 60.85935��\n   Dec (J2000): -75�� 22��� 43.8��� = -75.3788��\n   Error: 3.4��� (radius, 90% conf., enhanced)\n   Count-rate: 0.019 (��0.004) ct s-1\n   Distance: 36.6 arcsec from IPN position\n\nSource 3:\n   RA (J2000): 04h 03m 57.93s = 60.99137��\n   Dec (J2000): -75�� 21��� 26.8��� = -75.3574��\n   Error: 7.1��� (radius, 90% conf.)\n   Count-rate: 2.6 (+1.9, -1.3) ��10-3 ct s-1\n   Distance: 175 arcsec from IPN position\n\n\nSource 2 is below the RASS limit and shows no definitive signs of\nfading. Therefore, at the present time we cannot confirm this as the\nafterglow. Source 3 is at a position consistent with a QSO candidate\n(Wu et al., 2023, RAA, 23, 025006) and therefore is likely unrelated to\nGRB 230307A. Further observations are ongoing. \n\n\nThe results of the XRT-team automatic analysis of the tiled XRT\nobservations, including a position-specific upper limit calculator, are\navailable at https://www.swift.ac.uk/xrt_products/TILED_GRB00110. \n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 33429,
  "createdOn": 1678317437000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 230307A: Swift-XRT observations",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 230307A"
}