{
  "bibcode": "2021GCN.29750....1E",
  "body": "P.A. Evans (U. Leicester), M. Capalbi (INAF-IASFPA), M. Perri (SSDC &\nINAF-OAR), V. D'Elia (SSDC & INAF-OAR), J.A. Kennea (PSU), A.\nTohuvavohu (U. Toronto), B. Sbarufatti (PSU), J.P. Osborne (U.\nLeicester) and K.L. Page report on behalf of the Swift-XRT team:\n\nWe have analysed 6.0 ks of XRT data for GRB 210402A (Page et al. GCN\nCirc. 29743), from 160 s to 46.0 ks after the  BAT trigger. The data\ncomprise 1.1 ks in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. Using 1629 s of PC mode data and 3 UVOT\nimages, we find an enhanced XRT position (using the XRT-UVOT alignment\nand matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =\n198.25927, +44.51454 which is equivalent to:\n\nRA (J2000): 13h 13m 02.22s\nDec(J2000): +44d 30' 52.3\"\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+5.4 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.03 (+0.21, -0.27).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.811 (+0.027, -0.026). The\nbest-fitting absorption column is  3.25 (+/-0.13) x 10^21 cm^-2, in\nexcess of the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 2.09 (+0.20, -0.19)\nand a best-fitting absorption column of 3.2 (+/-0.8) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.6 x 10^-11 (5.6 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.2 (+/-0.8) x 10^21 cm^-2\nGalactic foreground: 1.5 x 10^20 cm^-2\nExcess significance: 6.5 sigma\nPhoton index:\t     2.09 (+0.20, -0.19)\n\nIf the light curve continues to decay with a power-law decay index of\n1.03, the count rate at T+24 hours will be 0.017 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.0 x\n10^-13 (9.4 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/01040123.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29750,
  "createdOn": 1617454421000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210402A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210402A"
}