{
  "bibcode": "2011GCN.12348....1D",
  "body": "P. D'Avanzo (INAF-OAB), J. K. Cannizzo (NASA/UMBC), P.A. Evans and M.R. Goad\n(U. Leicester) report on behalf of the Swift-XRT team:\n\nAt 04:36:53 UT, September 16, 2011, Swift began a Target of Opportunity\nobservation of the AGILE discovered burst GRB 110915B (Del Monte et al. et\nal. GCN Circ. 12341).\n\nWe have analysed 2.1 ks of XRT data, from 36.8 ks to 43.2 ks after the\nAGILE trigger. The data are entirely in Photon Counting (PC) mode.  An\nuncatalogued X-ray source is detected within the AGILE error circle. Using\n2132 s of PC mode data and 3 UVOT images, we find an enhanced XRT position\n(using the XRT-UVOT alignment and matching UVOT field sources to the\nUSNO-B1 catalogue): RA, Dec = 77.55470, +1.93280 which is equivalent to:\n\nRA (J2000): 05h 10m 13.13s\nDec(J2000): +01d 55' 57.9\"\n\nwith an uncertainty of 1.8 arcsec (radius, 90% confidence). This position\nis 37 arcsec from the AGILE position. The light curve is consistent with a\nconstant source of mean count rate 7.1e-02 ct/sec. A power-law fit gives\nan index of -0.3 (+2.3, -1.1).\n\nA spectrum formed from the PC mode data can be fitted with an absorbed\npower-law with a photon spectral index of 1.85 (+0.36, -0.27). The\nbest-fitting absorption column is  9 (+10, -1) x 10^20 cm^-2, consistent\nwith 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 deduced\nfrom this spectrum  is 3.9 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1.\n\nA summary of the PC-mode spectrum is thus:\nTotal column:             9 (+10, -1) x 10^20 cm^-2\nGalactic foreground: 8.5 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:             1.85 (+0.36, -0.27)\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00020185.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 12348,
  "createdOn": 1316174721000,
  "email": "paolo.davanzo@brera.inaf.it",
  "subject": "GRB 110915B: XRT afterglow candidate",
  "submitter": "Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>",
  "eventId": "GRB 110915B"
}