{
  "bibcode": "2022GCN.31410....1B",
  "body": "D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), K.L. Page (U.\nLeicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T.\nSbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB) and P.A. Evans (U.\nLeicester) report on behalf of the Swift-XRT team:\n\nSwift-XRT has performed follow-up observations of the\nSwift/BAT-GUANO-detected burst GRB 220107A (DeLaunay et al. GCN Circ.\n31402), collecting 699 s of Photon Counting (PC) mode data between\nT0+26.7 ks and T0+27.4 ks. \n\nAn uncatalogued X-ray source is detected and is above the RASS 3-sigma\nupper limit at this position, and is therefore likely the GRB\nafterglow. Using 698 s of PC mode data and 1 UVOT image, we find an\nenhanced XRT position (using the XRT-UVOT alignment and matching UVOT\nfield sources to the USNO-B1 catalogue): RA, Dec = 169.80648, +34.17014\nwhich is equivalent to:\n\nRA (J2000): 11h 19m 13.55s\nDec(J2000): +34d 10' 12.5\"\n\nwith an uncertainty of 2.3 arcsec (radius, 90% confidence). This\nposition is 3.0 arcmin from the Swift/BAT-GUANO position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=2.5 (+0.5, -2.4).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.84 (+0.27, -0.18). The\nbest-fitting absorption column is  3.1 (+6.1, -0.9) x 10^20 cm^-2,\nconsistent with the Galactic value of 2.2 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 3.5 x 10^-11 (3.7 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.1 (+6.1, -0.9) x 10^20 cm^-2\nGalactic foreground: 2.2 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.84 (+0.27, -0.18)\n\nIf the light curve continues to decay with a power-law decay index of\n2.5, the count rate at T+24 hours will be 0.054 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x\n10^-12 (2.0 x 10^-12) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00021476.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021476.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 31410,
  "createdOn": 1641623965000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 220107A: Swift-XRT afterglow detection",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 220107A"
}