{
  "bibcode": "2021GCN.30023....1O",
  "body": "J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), E. Ambrosi \n(INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR),\nB. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), A.P.\nBeardmore (U. Leicester) and A. D'Ai report on behalf of the Swift-XRT\nteam:\n\nWe have analysed 7.0 ks of XRT data for GRB 210515C (D'Ai et al. GCN\nCirc. 30020), from 76 s to 29.8 ks after the  BAT trigger. The data\ncomprise 98 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. Using 1614 s of PC mode data and 3 UVOT images, we\nfind an enhanced XRT position (using the XRT-UVOT alignment and\nmatching UVOT field sources to the USNO-B1 catalogue): RA, Dec =\n1.09417, -14.95334 which is equivalent to:\n\nRA (J2000): 00h 04m 22.60s\nDec(J2000): -14d 57' 12.0\"\n\nwith an uncertainty of 2.3 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=2.63 (+0.13, -0.12), followed by a break at T+853 s to\nan alpha of 0.57 (+/-0.14).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 3.06 (+0.24, -0.21). The\nbest-fitting absorption column is  1.7 (+/-0.4) x 10^21 cm^-2, in\nexcess of the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.11 (+0.26, -0.23)\nand a best-fitting absorption column of 6.4 (+5.7, -3.8) x 10^20 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.1 x 10^-11 (3.7 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     6.4 (+5.7, -3.8) x 10^20 cm^-2\nGalactic foreground: 2.6 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     2.11 (+0.26, -0.23)\n\nIf the light curve continues to decay with a power-law decay index of\n0.57, the count rate at T+24 hours will be 3.8 x 10^-3 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x\n10^-13 (1.4 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01048618.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 30023,
  "createdOn": 1621148716000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210515C: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210515C"
}