{
  "bibcode": "2007GCN..6337....1S",
  "body": "G. Stratta (ASDC), M. Perri (ASDC), D.N. Burrows (PSU) and\nM. Stamatikos (NASA/ORAU) report on behalf of the Swift XRT\nteam:\n\nWe have analyzed the first four orbits of Swift-XRT data on\nGRB 070420 (Stamatikos et al. GCN 6330), with a total exposure\nof 573 s in Windowed Timing (WT) mode and of 7.5 ks in Photon\nCounting (PC) mode. This provides a refined XRT position at\nRA,Dec(deg)=121.230194683,-45.5562815181  which is:\n\nRA(J2000)=08h 04m 55.22s\nDec(J2000)=-45d 33' 22.6\"\n\nwith an estimated error radius of 3.5 arcseconds (90% confidence).\nThis position is 62.3 arcseconds from the BAT position\n(Stamatikos et al. GCN 6330), 0.8 arcseconds from the initial XRT\nposition (Stamatikos et al. GCN 6330) and 2.6 arcseconds from the\nUVOT refined optical counterpart position\n(Holland et al. GCN 6336).\n\nThe 0.3-10 keV X-ray light curve presents a steep decay between\nT+106 s and T+300 s followed by a plateau phase up to about\nT+2ks (end of the first orbit). The last three orbits of data\ntaken in PC mode show a new steepening of the light curve,\nfrom T+5ks to T+18.5 ks (end of the third orbit).\nThe light curve from T+106 s to T+18.5 ks is well fit by a\ndouble broken power law model with decay indices:\nd1=-4.4+/-0.2, d2=-0.2+/-0.1 and d3=-1.5+/-0.1 and with the\nfirst break at about t1=230s and the second break at about\nt2=3200s.\n\nThe 0.3-10.0 keV X-ray spectrum from the XRT/WT data during the\ndecay phase is well fit by an absorbed power law with a photon\nindex of 2.6 +/- 0.1 and a total column density of\nNH=(4.1+/-0.3)e21 cm**-2. The X-ray spectrum from the XRT/PC\ndata during the flat decay phase (corrected from the pileup\neffects) can be fit by an absorbed power law with a photon index\nof 2.0+/-0.2 and a total column density of\nNH=(5.0+/-1.0)e21 cm**-2. We note that the Galactic column\ndensity in the direction of the source is 3.7e21 cm**-2\n(Dickey & Lockman 1990).\n\nAssuming the X-ray emission continues to decline with decay index\nd3, we predict a 0.3-10.0 keV XRT count rate of 1.3e-2 count/s at\nT+24h and 4.7e-3 count/s at T+48h, which corresponds to an\nobserved 0.3-10.0 keV flux of 7e-13 erg/cm**2/s and\n2.5e-13 erg/cm**2/s, respectively.\n\nThis circular is an official product of the Swift Team.",
  "circularId": 6337,
  "createdOn": 1177094089000,
  "email": "stratta@asdc.asi.it",
  "subject": "GRB 070420: Swift XRT refined analysis",
  "submitter": "Giulia Stratta at ASDC  <stratta@asdc.asi.it>",
  "eventId": "GRB 070420"
}