{
  "bibcode": "2007GCN..6644....1E",
  "body": "P.A. Evans (U. Leicester) and H. Ziaeepour (UCL-MSSL) report on behalf of \nthe Swift/XRT team:\n\nWe have analyzed the first 1.3 ks of Swift XRT data for GRB 070721A \n(Ziaeepour et al. GCN Circ. 6639), comprising 35 s in Windowed Timing (WT) \nmode, and 1.3 ks in Photon Counting (PC) mode. The burst is clearly \ndetected. Using 799 s of overlapping XRT Photon Counting mode and UVOT \nV-band data, we find an astrometrically corrected X-ray position (using \nthe XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 \ncatalogue): RA, Dec = 3.16348, -28.55017 which is equivalent to:\n\nRA (J2000):  00 12 39.24\nDec (J2000): -28 33 00.6\n\nwith an uncertainty of 2.3 arcsec (radius, 90% confidence). This position \nis 3.2\" from the initial XRT position reported in GCN Circ. 6639, and 95\" \nfrom the BAT-refined position reported by Sakamoto et al. (GCN Circ. \n6642).\n\nThe XRT light curve shows a fading behaviour, which is well fitted by a \nbroken power-law. The initial decay followed a slope of alpha=2.97 \n(+0.57/-0.42). At T0+281 (+112/-71) s the decay shallows to an alpha of \n0.75 (+0.39/-0.49).\n\nThe Photon Counting mode spectrum is well fitted by an absorbed power-law, \nwith a column density of 1.61e20 cm^-2 (the Galactic value) and a gamma of \n2.24 (+0.33/-0.26). This is consistent with the value derived for the BAT \nspectrum (GCN Circ 6642). The observed (unabsorbed) 0.3-10 keV flux is \n6.53e-12 (8.23e-12) erg cm^-2 s^-1.\n\nIf the source continues to decay at the same rate, we predict a count rate \nof 2.7e-3 counts/s at T0+24 hours, which corresponds to an observed \n(unabsorbed) flux of 1.87e-13 (2.36e-13) erg cm^-2 s^-1.\n\nThis circular is an official product of the Swift/XRT team.",
  "circularId": 6644,
  "createdOn": 1185028271000,
  "email": "pae9@star.le.ac.uk",
  "subject": "GRB 070721A: Swift/XRT refined analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@star.le.ac.uk>",
  "eventId": "GRB 070721A"
}