{
  "bibcode": "2009GCN..9777....1S",
  "body": "R. Starling (U. Leicester) and M. Stamatikos (NASA/ORAU) report on behalf \nof the Swift-XRT team:\n\nWe have analysed the first two orbits of Swift XRT data for GRB 090812 \n(trigger=359711, Stamatikos et al. GCN Circ. 9768) spanning T0+78 s to \nT0+12.4 ks. The UVOT-enhanced XRT position was given by Goad et al. in GCN \nCirc. 9748.\n\nThe light curve shows initial flaring, with two large flares overlaid on a \npower law of decay slope alpha1=1.5+/-0.5. The power law then breaks at \napproximately 960 s to a shallower slope of alpha=1.05+/-0.10.\n\nA power law is an acceptable fit to a spectrum formed from the first orbit \nwindowed timing (WT) mode data centred at T0+230 s, with a photon index, \nGamma, of 1.97+/-0.03. The resulting column density at the source \n(z=2.452, de Ugarte Postigo et al. GCN Circ. 9771) is (1.00+/-0.09)e22 \ncm^-2 in addition to the Galactic column of 2.26e20 cm^-2 (Kalberla et al. \n2005). \nThe 0.3-10 keV observed (unabsorbed) count to flux conversion is 1 ct = \n3.4e-11 (4.2e-11) erg/cm2/s.\nA fit to the spectrum formed from the first and second orbit photon \ncounting (PC) mode data centred at T0+2760 s is consistent with the WT \nspectral results.\n\nInterestingly, the X-ray spectral slope we derive is consistent with slope \nreported for the optical data from GROND, centred at T0+7860 s (Updike et \nal. GCN Circ. 9773.), which may imply a single spectral slope between\nthe X-ray and optical bands several thousand seconds after the trigger. \n\nWhile we only have two orbits of data, if we assume the light curve \ncontinues to decay with a power law of index alpha=1.05, the \npredicted count rate at T+24 hours will be 0.023 count s^-1, \ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 7.7e-13 \n(9.5e-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/00359711.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9777,
  "createdOn": 1250090367000,
  "email": "rlcs1@star.le.ac.uk",
  "subject": "GRB 090812: Swift XRT refined analysis",
  "submitter": "Rhaana Starling at U of Leicester  <rlcs1@star.le.ac.uk>",
  "eventId": "GRB 090812"
}