{
  "bibcode": "2007GCN..6172....1P",
  "body": "K.L. Page (U. Leicester) and S.B. Pandey (UCL-MSSL) report on behalf of \nthe Swift-XRT team:\n\nWe have analysed the first three orbits of Swift-XRT data obtained for GRB\n070306 (Pandey et al., GCN Circ. 6169), which includes 156 s of Windowed\nTiming (WT) data and 3.3 ks of Photon Counting (PC) mode data. Using the\nPC data we derive a refined position of RA, Dec = 148.0974, 10.4820, which\nis equivalent to\n\nRA(J2000)  =  09 52 23.39\nDec(J2000) = +10 28 55.3\n\nwith an estimated error radius of 3.6 arcsec (90% confidence). This lies\n67 arcsec and 3.3 arcsec from the onboard BAT and XRT positions given in\nGCN Circ. 6169, respectively.\n\nThe XRT light-curve initially decays between ~155 and 165 seconds after\nthe trigger, followed by a small increase in count rate until 180 seconds;  \nafter this time, the curve shows a steep decay, with alpha_1 = 6.3 +/- 0.2\nuntil 411 +/- 17 seconds post-trigger, at which point the decay flattens\nto alpha_2 = 0.22 +/- 0.08. All error bars are at the 90% confidence\nlevel. Note that Swift triggered on a precursor; if T0 for the light-curve\nfits were to be referenced to the main peak of the burst, around 100\nseconds later, this initial decay would not be so steep.\n\nThe WT spectrum can be modelled by a power-law of Gamma = 2.29 +/- 0.05,\nwith a total absorbing column of 3.9x10^21 cm^-2, compared to the Galactic\ncolumn of 2.94x10^20 cm^-2 in this direction. This value of NH was\ncalculated from the later PC data (Gamma = 2.14 +/- 0.17), when the\nspectral evolution apparent during the initial steep decay has ceased. The\nmean observed (unabsorbed) flux over 0.3-10 keV for this WT spectrum is\n1.73e-9 (3.48e-9) erg cm^-2 s^-1.\n\nIf the decay continues with a slope of alpha = 0.22, the count rate is\npredicted to be 0.21 count s^-1 at 24 hours. This corresponds to an\nobserved flux of 1.0e-11 erg cm^-2 s^-1 (over 0.3-10 keV), with the \nunabsorbed value being 1.9e-11 erg cm^-2 s^-1, using the spectral fit to \nthe PC data.\n\nThis circular is an official product of the XRT team.",
  "circularId": 6172,
  "createdOn": 1173223969000,
  "email": "kpa@star.le.ac.uk",
  "subject": "GRB 070306: XRT Team Refined Analysis",
  "submitter": "Kim Page at U.of Leicester  <kpa@star.le.ac.uk>",
  "eventId": "GRB 070306"
}