{
  "bibcode": "2021GCN.29625....1P",
  "body": "M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti\n(PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U.\nLeicester), K.L. Page (U. Leicester) and A. D'Ai (INAF-IASFPA) report\non behalf of the Swift-XRT team:\n\nWe have analysed 11 ks of XRT data for GRB 210305A (D'Ai et al. GCN\nCirc. 29595), from 67 s to 178.1 ks after the  BAT trigger. The data\ncomprise 184 s in Windowed Timing (WT) mode (the first 9 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. Using 2502 s of PC mode data and 4 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 = 319.81054, +34.55403\nwhich is equivalent to:\n\nRA (J2000): 21h 19m 14.53s\nDec(J2000): +34d 33' 14.5\"\n\nwith an uncertainty of 1.4 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+5.3 ks) can be modelled with a\npower-law decay with a decay index of alpha=0.91 (+0.10, -0.09).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.44 (+/-0.08). The\nbest-fitting absorption column is  3.2 (+0.5, -0.4) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.0 x 10^21 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.84 (+/-0.16) and a\nbest-fitting absorption column of 4.0 (+0.9, -0.8) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 4.3 x 10^-11 (6.1 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     4.0 (+0.9, -0.8) x 10^21 cm^-2\nGalactic foreground: 2.0 x 10^21 cm^-2\nExcess significance: 4.1 sigma\nPhoton index:\t     1.84 (+/-0.16)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01035922.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29625,
  "createdOn": 1615222100000,
  "email": "antonino.dai@inaf.it",
  "subject": "GRB 210305A: Swift-XRT refined Analysis",
  "submitter": "Antonino D'Ai at IASF-PA  <antonino.dai@inaf.it>",
  "eventId": "GRB 210305A"
}