{
  "bibcode": "2021GCN.29622....1D",
  "body": "V. D'Elia (SSDC & INAF-OAR), A. D'Ai (INAF-IASFPA), D.N. Burrows (PSU),\nJ. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L.\nPage (U. Leicester), A.P. Beardmore (U. Leicester) and A. Melandri\n(INAF-OAB) report on behalf of the Swift-XRT team:\n\nWe have analysed 10 ks of XRT data for GRB 210306A (D'Elia et al. GCN\nCirc. 29597), from 65 s to 182.6 ks after the  BAT trigger. The data\ncomprise 576 s in Windowed Timing (WT) mode (the first 7 s were taken\nwhile Swift was slewing) with the remainder in Photon Counting (PC)\nmode. Using 3375 s of PC mode data and 9 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 = 129.95774, +60.20523\nwhich is equivalent to:\n\nRA (J2000): 08h 39m 49.86s\nDec(J2000): +60d 12' 18.8\"\n\nwith an uncertainty of 1.4 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=0.435 (+/-0.027), followed by a break at T+1548 s to an\nalpha of 1.58 (+/-0.06).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 1.89 (+0.05, -0.04). The\nbest-fitting absorption column is  1.53 (+0.15, -0.14) x 10^21 cm^-2,\nin excess of the Galactic value of 4.2 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.98 (+0.14, -0.13)\nand a best-fitting absorption column of 1.7 (+/-0.4) x 10^21 cm^-2. The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.5 x 10^-11 (4.7 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     1.7 (+/-0.4) x 10^21 cm^-2\nGalactic foreground: 4.2 x 10^20 cm^-2\nExcess significance: 5.2 sigma\nPhoton index:\t     1.98 (+0.14, -0.13)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01035994.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 29622,
  "createdOn": 1615219707000,
  "email": "valerio.delia@ssdc.asi.it",
  "subject": "GRB 210306A: Swift-XRT refined Analysis",
  "submitter": "Valerio D'Elia at ASDC  <valerio.delia@ssdc.asi.it>",
  "eventId": "GRB 210306A"
}