{
  "bibcode": "2007GCN..6452....1G",
  "body": "C. Guidorzi, P. Romano (Univ Bicocca&INAF-OAB), J. Hill (GSFC),\nA. Beardmore, P.A. Evans (U. Leicester), A. Moretti (INAF-OAB),\nreport on behalf of the Swift team:\n\nWe have analysed the first five orbits of GRB 070521 (Guidorzi\net al., GCN Circ. 6431) with total observing times of 10.2 ks in\nPhoton Counting mode in the Swift XRT.\nThe XRT position, using the UVOT to astrometrically correct the XRT field,\nassuming a fixed mapping between the XRT and UVOT instruments, is\nRA(J2000)=242.6608 deg, Dec(J2000)=+30.2561 deg, corresponding to:\n\nRA(J2000)  = 16h 10m 38.60s\nDec(J2000) = +30d 15' 21.8\"\n\nwith an uncertainty of 1.7 arcsec (radius, 90% containment).\nThis was based on 3 intervals of overlapping XRT/UVOT V-band data\ntotalling 866 s. The UVOT astrometry is performed relative to USNOB1.\n\nThis is 6.6 arcsec from the initial X-ray position,\n4.0 arcsec from the XRT position notice,\nand 17 arcsec from the BAT refined position (Palmer et al., GCN Circ. 6440).\n\nThe XRT light curve exhibits an initial flaring behaviour superposed\nto a power-law decay (index of 0.5 +/- 0.1) up to ~T+600 s.\nA break in the power-law decay is observed at T+(6.8 +/- 0.9) ks,\nafter which it steepens with a power-law index of 1.7 +/- 0.1\nup to T+34 ks (90% confidence intervals).\n\nWe extracted a spectrum of the PC data from T+4.7 ks to T+13 ks.\nThis can be fit with an absorbed power law with a photon index\nof 2.11 +/- 0.16 and column density of (7+/-1)E21 cm^-2\nsignificantly in excess of the Galactic value\n(2.8E20 cm^-2; Dickey & Lockman, 1990).\n\nThe absorbed (unabsorbed) 0.3-10.0keV flux for that spectrum\nis 1.6E-11 (3.2E-11) ergs cm^-2 s^-1.\n\nAssuming the source continues to decay at the same rate, we predict\nan XRT count rate of 7.9E-3 counts/s at T+24 hours, which corresponds\nto an observed (unabsorbed) flux of 4.6E-13 (9.3E-13) ergs cm^-2 s^-1.\n\nThis circular is an official product of the Swift XRT team.",
  "circularId": 6452,
  "createdOn": 1179824859000,
  "email": "cristiano.guidorzi@brera.inaf.it",
  "subject": "GRB 070521: Swift-XRT refined analysis",
  "submitter": "Cristiano Guidorzi at INAF-OAB  <cristiano.guidorzi@brera.inaf.it>",
  "eventId": "GRB 070521"
}