{
  "bibcode": "2005GCN..3695....1D",
  "body": "Andrea De Luca (IASF Mi) on behalf of a larger collaboraton \nreport:\n\nWe have analyzed the data from the XMM-Newton observation \nof GRB050713A, discovered by Swift on 2005, July 13 at \n04:29:02.39 UT (Falcone et al., GCN3581).\n\nThe XMM-Newton observation started on 2005, July 13 at \n10:18 UT and lasted for 30.7 ks. We report here on the \nanalysis of data collected with the EPIC/pn detector, \nwhich started observing the field at 10:54 UT (~6h 20min \nafter the GRB).\n\nAs reported by Loiseau et al. (GCN3594), the afterglow of \nGRB050713A is clearly detected in the pn image, at a \nposition fully consistent with the refined Swift/XRT one \n(Morris et al., GCN3606). \nExtracting source events from a circle of 25 arcsec radius \n(containing ~80% of the total counts), the time-averaged, \nbackground-subtracted count rate in the 0.2-8 keV range \nis 0.547+/-0.005 cts/s.\n\nThe afterglow is clearly seen to fade along the XMM-Newton \nobservation, spanning the time range 23.5-51.5 ks after \nthe GRB. The background-subtracted light curve (0.5-5 keV) \nis well fitted (reduced chi2=0.9, 26 d.o.f.) by a power law \ndecay with index delta=1.45+/-0.07 (90% c.l.). \nThe afterglow decay has significantly steepened with \nrespect to the epoch of the earlier Swift observation: \nMorris et al. (GCN 3606) observed an index delta=0.82+/-0.11\nin the time range 5-10 ks after the burst using Swift/XRT data. \nThis implies the presence of a break in the afterglow X-ray\nlight curve between 10 ks and 23.5 ks from the GRB.\n\nWe extracted the time-averaged spectrum and generated ad-hoc \nresponse and effective area files. We quote here errors at \n90% level for a single interesting parameter, unless otherwise \nspecified.\n\nA fit in the energy range 0.2-8 keV with an absorbed power \nlaw model yields a reduced chi2 of 1.25 for 172 d.o.f. \nThe resulting NH=(3.25+/-0.15)x10^21 cm^-2 is higher than \nthe expected Galactic value in the burst direction (NH=1.1x10^21 \ncm^-2, Dickey & Lockman, 1990); the best fitting power law photon \nindex is Gamma=2.16+/-0.05.\nSuch results are consistent with the XRT ones (Morris et al., \nGCN 3606), which implies no significant spectral evolution with\nrespect to the earlier phase of the afterglow.\n\nA better fit to the pn spectrum (reduced chi2=0.97, 171 dof) \nmay be obtained fixing the NH to the expected Galactic value \n(NH=1.1x10^21 cm^-2) and adding a neutral, redshifted absorber \ncomponent to the spectral model. With a simple F-test we evaluate \nthe chance occurrence probability of the improvement to be \nof 5x10^-11. The best fit value for the intrinsic NH is 4.0x10^21 \ncm^-2, while the best fit value for the redshift z is 0.55.\nAt 90% c.l. for 2 parameters, we obtain the following ranges:\nintrinsic NH=(0.4-3.2)x10^22 cm^-2; redshift z=(0.4-2.6).\nUsing such model, the resulting power law photon index is \nGamma=2.04+/-0.05.\nThe observed flux is of 2.2x10^-12 erg cm^-2 s^-1 in 0.2-10 keV;\nthe corresponding unabsorbed flux is of 3.8x10^-12 erg cm^-2 s^-1.\n\nAs a last step, we divided the pn dataset into two time intervals \nof ~9500 s and ~14600 s (each containing about half of the counts \nfrom the afterglow) and we repeated the spectral analysis. \nWe found no significant spectral changes in the two considered \nintervals.",
  "circularId": 3695,
  "createdOn": 1122578832000,
  "email": "deluca@mi.iasf.cnr.it",
  "subject": "GRB050713: analysis of the XMM-Newton observation",
  "submitter": "Andrea De Luca at IASF-CNR,Milano  <deluca@mi.iasf.cnr.it>",
  "eventId": "GRB 050713"
}