{
  "bibcode": "2007GCN..6852....1S",
  "body": "R. Starling, J.P. Osborne, K.L. Page (U. Leicester) and F.E. Marshall\n(NASA/GSFC) report, on behalf of the Swift XRT team:\n\nPreviously, Swift XRT data for the short GRB 070810B (trigger=287409; \nMarshall et al., GCN Circ. 6743) up to 13.8 ks after the BAT trigger \nshowed two possible sources within the BAT refined error circle, detected \nat 2-sigma significance in 7.2 ks and termed S1 and S2 (Starling et al., \nGCN Circ. 6754).\n \nWe have analysed a further 12.6 ks of Swift XRT photon counting mode data\nbeginning 42 days and ending 54 days after the burst, in order to assess \nthe variability of the two possible afterglow candidates.\n\nIn this second epoch of data we detect one X-ray source at 4-sigma \nsignificance within the refined BAT error circle (Sakamoto et al., GCN \nCirc. 6753), corresponding to the source S2 described in GCN Circ. 6754.\nUsing Bayesian analysis we find that S2 has between 20 and 54 counts at \nthe 99% confidence level or 1.6e-3 to 4.3e-3 count/s, consistent with the \nfirst epoch limits of 5.6e-4 to 3.6e-3 count/s. This suggests that S2 is \na persistent faint source, and not the afterglow of GRB 070810B.\n \nThe possible source S1 (GCN Circ. 6754), detected only at the 2-sigma \nlevel in the intial epoch observations, is not detected in the second \nepoch observations, providing an upper limit on the count rate of 6.7e-4 \ncount/s at 99% confidence based on the background count rate. This is  \nabove the 3-sigma lower limit on the source count rate at epoch 1 of \n5.6e-4 count/s, hence we cannot determine whether or not this source has \nfaded. \n \nThis is an official product of the Swift XRT team.",
  "circularId": 6852,
  "createdOn": 1191609235000,
  "email": "rlcs1@star.le.ac.uk",
  "subject": "GRB 070810B: further XRT analysis",
  "submitter": "Rhaana Starling at U of Leicester  <rlcs1@star.le.ac.uk>",
  "eventId": "GRB 070810B"
}