{
  "bibcode": "2004GCN..2698....1D",
  "body": "A. DeLuca & D. Gotz (IASF-Mi), S. Campana (OA Brera) on behalf of a larger\ncollaboration report:\n\n\"We have analysed the data XMM-Newton observation of GRB 040827 (Gotz et \nal.\nGCN 2670). A preliminary account of these data has been given by\nRodriguez-Pascual & Gonzalez-Riestra (GCN 2688).\n\nThe observation started on 2004-08-27 at 18:07:56.UT, lasting 54.3 ks.\nThanks to quick-look data it was soon realised that an afterglow was \npresent\nbut it was more than 1arcmin off the camera boresight. Therefore, the \ntelescope\nwas re-pointed during the observation (causing problems in the generation\nof the ancillary file for spectral analysis).\n\nThe source intensity profile is consistent within errors with the\ninstrumental PSF (possible earlier reports of an extended source might be\ndue to the re-pointing of the satellite).\nAstrometry of the XMM-Newton/EPIC images was done by matching X-ray\nsources in the field to stars in the USNO-B1 catalogue. The refined\nposition (J2000) for the X-ray afterglow (source XMMUJ151701.3-160828,\nGCN 2678) is: RA(2000) 15h 17m 01.39s, Dec(2000):-16d 08' 28.77''.\nThe positional accuracy is at a level of 1.5'' (68% c.l.).\nThis position is consistent with earlier reports (Rodriguez-Pascual &\nGonzalez-Riestra GCN 2688, XMM-2) and with the position of the likely\nafterglow established based on optical-NIR data (Berger et al. GCN 2680;\nGladders & Berger GCN 2681; Kaplan & Berger GCN 2683; Tanvir et al. GCN \n2684;\nMalesani et al. GCN 2685).\n\nWe extracted spectra from the three EPIC cameras. We took the arf file\nfrom the same region of extraction of a different observation.\nA single absorbed power law model provides a good description of the data\n(chi2_red=1.2 with 187 degrees of freedom), however the column density\n(N_H=3.7_{-1.2}^{+4.2}x10^21 cm-2, errors at 90% c.l.) is much larger\nthan the column density in this direction of the Galaxy (N_H=8x10^20 cm-2,\nDickey & Lockman 1990, or N_H=5x10^20 cm-2 based on Schlegel et al. 1998 \nmaps).\nFixing the column density to N_H=8x10^20 cm-2 results in a unacceptable fit\nwith chi2_red=3.0.\nWe then include an absorption component at the redshift of the afterglow,\nkeeping fixed the Galactic column density to N_H=8x10^20 cm-2.\nThe new fit is good (chi2_red=1.0) providing a heavily absorbed \nafterglow with\nN_H=1.3_{-0.3}^{+0.6}x10^22 cm-2. The redshift is relatively well \nconstrained to\nz=0.9_{-0.2}^{+0.9}. The power law photon index is Gamma=2.3+/-0.1 and\nthe unabsorbed 0.5-10 keV flux is 3.4x10^{-13} erg cm-2 s-1.\n\nThe 0.2-10 keV pn light curve shows a clear decay in time. We excluded from\nthis analysis the first 4 ks when the XMM-Newton pointing was not \ndefinitive.\nA power law decay with t^{-1.6+/-0.2} can account for the main decay.\"\n\nThis message can be cited.",
  "circularId": 2698,
  "createdOn": 1094666994000,
  "email": "campana@merate.mi.astro.it",
  "subject": "GRB040827: analysis of the XMM-Newton observation",
  "submitter": "Sergio Campana at INAF-OAB  <campana@merate.mi.astro.it>",
  "eventId": "GRB 040827"
}