{
  "bibcode": "2021GCN.30172....1S",
  "body": "B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), K.L. Page\n(U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB),\nT. Sbarrato (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 Swift/BAT-GUANO\ndetected burst GRB 210606A (James DeLaunay et al. GCN Circ. 30134),\ncollecting 7.3 ks of Photon Counting (PC) mode data between T0+62.3 ks\nand T0+385.7 ks. \n\nFour uncatalogued X-ray sources are detected consistent with being\nwithin 394 arcsec of the Swift/BAT position, of which one (\"Source 1\")\nis fading with 4.6-sigma significance, and is therefore likely the GRB\nafterglow. Using 4521 s of PC mode data and 5 UVOT images, we find an\nenhanced XRT position (using the XRT-UVOT alignment and matching UVOT\nfield sources to the USNO-B1 catalogue): RA, Dec = 170.94110, +0.81293\nwhich is equivalent to:\n\nRA (J2000): 11h 23m 45.86s\nDec(J2000): +00d 48' 46.5\"\n\nwith an uncertainty of 2.3 arcsec (radius, 90% confidence). This\nposition is 6.1 arcmin from the Swift/BAT position. \n\nThe light curve can be modelled with a power-law decay with a decay\nindex of alpha=1.1 (+0.9, -0.6).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.8 (+0.5, -0.4). The\nbest-fitting absorption column is  1.4 (+1.6, -1.0) x 10^21 cm^-2,\nconsistent with the Galactic value of 3.8 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 (4.3 x\n10^-11) erg cm^-2 count^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.4 (+1.6, -1.0) x 10^21 cm^-2\nGalactic foreground: 3.8 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.8 (+0.5, -0.4)\n\nThe results of the XRT-team automatic analysis of the likely afterglow\nare at https://www.swift.ac.uk/ToO_GRBs/00021451/Source1.php.\nThe results of the full analysis of the XRT observations are available\nat https://www.swift.ac.uk/ToO_GRBs/00021451.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 30172,
  "createdOn": 1623356003000,
  "email": "aaron.tohu@gmail.com",
  "subject": "GRB 210606A: Swift-XRT afterglow detection",
  "submitter": "Aaron Tohuvavohu at U Toronto  <aaron.tohu@gmail.com>",
  "eventId": "GRB 210606A"
}