{
  "bibcode": "2009GCN..8956....1E",
  "body": "P. A. Evans and K.L. Page (U Leicester) report on behalf of the \nSwift-XRT team:\n\nWe have analysed 4.4 ks of XRT data for GRB 090308 (Evans et al. GCN\nCirc. 8948), from 130 s to 12.2 ks after the BAT trigger. The data\ncomprise 55 s in Windowed Timing (WT) mode with the remainder in Photon\nCounting (PC) mode. Using 460 s of PC mode data and 1 UVOT image, we\nfind an enhanced XRT position (using the XRT-UVOT alignment and matching\nUVOT field sources to the USNO-B1 catalogue): RA, Dec = 183.50120,\n-48.81710 which is equivalent to:\n\nRA (J2000): 12 14 0.28\nDec(J2000): -48 49 01.6\n\nwith an uncertainty of 1.6 arcsec (radius, 90% confidence).\n\nThe light curve can be modelled with an initial power-law decay with an\nindex of alpha=2.63 (+0.16, -0.13), followed by a break at T+830 s to an\nalpha of 1.2 (+0.5, -1.9).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.93 (+0.28, -0.26). The\nbest-fitting absorption column is 2.86 (+1.01, -0.88) x 10^21, in excess\nof the Galactic value of 8.5 x 10^20 cm^-2 (Kalberla et al. 2005). The\ncounts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum is 4.5 x 10^-11 (6.8 x 10-11) erg cm^-2\ncount^-1.\n\nIf the light curve continues to decay with a power-law decay index of\n1.9, the count rate at T+24 hours will be 2.0 x 10^-4 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.1 x \n10^-15 (1.4 x 10^-14) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00345777.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 8956,
  "createdOn": 1236584026000,
  "email": "pae9@star.le.ac.uk",
  "subject": "GRB 090308: Swift-XRT refined analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@star.le.ac.uk>",
  "eventId": "GRB 090308"
}