{
  "bibcode": "2022GCN.32135....1S",
  "body": "B. Sbarufatti (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U.\nLeicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.\nAmbrosi  (INAF-IASFPA) , D.N. Burrows (PSU), J. D. Gropp (PSU) and P.A.\nEvans (U. Leicester) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nFermi/LAT-detected burst GRB 220527A (Bissaldi et al. GCN Circ. 32131),\ncollecting 1.7 ks of Photon Counting (PC) mode data between T0+30.1 ks\nand T0+31.9 ks. \n\nTwo uncatalogued X-ray sources are detected, of which one (\"Source 2\")\nis above the RASS 3-sigma upper limit at this position, and is\ntherefore likely the GRB afterglow. Using 1733 s of PC mode data and 1\nUVOT image, we find an enhanced XRT position (using the XRT-UVOT\nalignment and matching UVOT field sources to the USNO-B1 catalogue):\nRA, Dec = 323.52805, -14.97183 which is equivalent to:\n\nRA (J2000): 21h 34m 06.73s\nDec(J2000): 14d 58' 18.6\"\n\nwith an uncertainty of 2.6 arcsec (radius, 90% confidence). This\nposition is 4.9 arcmin from the Fermi/LAT position.  The light curve is\nconsistent with a constant source of mean count rate 3.9e-01 ct/sec. A\npower-law fit gives an index of 0.6 (+2.5, -1.1).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.83 (+0.21, -0.20). The\nbest-fitting absorption column is  9.8 (+6.1, -3.5) x 10^20 cm^-2,\nconsistent with the Galactic value of 6.2 x 10^20 cm^-2 (Willingale et\nal. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux\nconversion factor deduced from this spectrum  is 3.6 x 10^-11 (4.2 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     9.8 (+6.1, -3.5) x 10^20 cm^-2\nGalactic foreground: 6.2 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.83 (+0.21, -0.20)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021503.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021503.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 32135,
  "createdOn": 1653700203000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 220527A: Swift-XRT afterglow detection",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 220527A"
}