{
  "bibcode": "2009GCN..9163....1M",
  "body": "Mangano V., Sbarufatti B. (INAF-IASFPA) report on behalf of the\nSwift XRT Team:\n\nWe have analysed the first four orbits of Swift-XRT data obtained from\nGRB 090418 (trigger 349510; Mangano, et al., GCN Circ. 9149),\ncomprising 116 s taken in Windowed Timing (WT) mode, from T+102 s to\nT+218 s, and a total exposure of 8.5 ks in Photon Counting (PC)\nmode from T+219 s to the end of the observation at T+18 ks.\n\nThe best position of the X-ray afterglow is the UVOT enhanced XRT\nposition given in Goad, et al., GCN Circ. 9154, that is\nRA, Dec = 269.31329, +33.40607 which is equivalent to:\n\nRA (J2000): 17h 57m 15.19s\nDec (J2000): +33d 24' 21.8\"\n\nwith an uncertainty of 1.7 arcsec (radius, 90% confidence).\n\nThe 0.3-10 keV X-ray light curve is well fitted by a doubly broken\npawer law, with a initial decay slope alpha1=1.7+/-0.1,\na first breal at about T+245 s, an intermediate decay slope\nalpha2=0.35 -0.1+0.06, a second break at about T+2 ks and\na final decay slope alpha3=1.39+/-0.06\nIf decaying at this rate, the afterglow will reach a count-rate of\n6.1E-3 counts/s at T+48h.\n\nThe average WT spectrum (corresponding to the initial steep decay phase)\nis best fitted by an absorbed power-law model, with photon index 2.0+/-0.2,\nand intrinsic NH=(6+/-3)E21 cm-2 (at the redshift z=1.608,\nChornock, et al., GCN circ. 9151) in excess with respect to the galactic\nabsorption value of 3.6E20 cm-2 (Kalberla et al. 2005).\nThe average observed(unabsorbed) flux in the 0.3-10 keV band is\n3.5(4.6)E-10 ergs cm-2 s-1.\nThe average PC spectrum of the first orbit (covering the intermediate\nslowly decaying phase) is well fitted by an absorbed power-law model,\nwith photon index 2.1+/-0.1, intrinsic NH=(1.2+/0.3)E22 cm-2\nand average observed(unabsorbed) flux in the 0.3-10 keV band of\n1.5(2.2)E-10 ergs cm-2 s-1.\nFinally, the average PC spectrum from T+4.2 ks to T+18 ks (orbits 2-4)\nis well fitted by an absorbed power-law model,\nwith photon index 2.0+/-0.1, intrinsic NH=(1.1+/0.2)E22 cm-2\nand average observed(unabsorbed) flux in the 0.3-10 keV band of\n1.3(1.8)E-11 ergs cm-2 s-1.\nThe average count-rate to observed(unabsorbed) flux conversion factor\nis 4.5(6.5)E-11.\nAll quoted errors are at 90% confidence level.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/00349510.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 9163,
  "createdOn": 1240160119000,
  "email": "vanessa@ifc.inaf.it",
  "subject": "GRB 090418: Swift XRT refined analysis",
  "submitter": "Vanessa Mangano at INAF-IASFPA  <vanessa@ifc.inaf.it>",
  "eventId": "GRB 090418"
}