{
  "bibcode": "2005GCN..3293....1D",
  "body": "Andrea De Luca (IASF Mi), Diego Gotz (IASF Mi), Sergio Campana (OAB)\non behalf of a larger collaboraton report:\n\nWe have analyzed the data from the XMM-Newton observation of\nGRB050326, discovered by Swift on 2005, Mar 26, 09:53:55 UTC\n(Markwardt et al., GCN3143).\n\nThe XMM-Newton observation started on 2005, Mar. 26 at 18:25 UTC\nand lasted for ~45.8 ks.\n\nA high particle background level affects the whole observation,\nwith several soft proton flares, particularly evident in pn data.\n\nWe improved the astrometry of the XMM-Newton/EPIC images\nby matching X-ray sources in the field to stars in the USNO-B1\ncatalogue. The refined position (J2000) for the X-ray afterglow is\n\nRA: 00h 27m 49.1s  Dec: -71d 22' 16.3\"\n\nThe 1 sigma error radius is 1.5 arcsec (including the rms error on\nthe cross-correlation as well as systematic uncertainties in the\noptical catalogue). The position is fully consistent with the XRT\ncoordinates (Moretti et al., GCN3147) as well as with the preliminary\nXMM-Newton position by Ehle & Perez-Martinez (GCN3149).\n\nThe MOS light curve (0.3-8 keV) is well fitted by a power law decay\nwith index delta=1.81+/-0.11 (90% confidence level), with a reduced\nchi2 of 0.6 (21 dof). Adding pn data (with a larger bkg contamination)\nyields fully consistent results (delta=1.85+/-0.10), but with a poorer\nfit quality (owing to bkg fluctuations).\n\nWe extracted time-averaged spectra from the three EPIC cameras and\nwe generated ad-hoc response files. We quote here errors at 90%\nconfidence level for a single interesting parameter unless otherwise\nspecified.\nA simultaneous fit with an absorbed power law model yields a reduced\nchi2 of 1.11 (241 dof). The resulting NH=(1.20+/-0.15)x10^21 cm^-2\nis higher than the expected Galactic value in the burst direction\n(NH=4.5x10^20 cm^-2, Dickey & Lockman, 1990); the best fitting power\nlaw photon index is Gamma=2.10+/-0.05.\n\nA better fit (reduced chi2=1.05, 240 dof) may be obtained\nfixing the NH to the expected Galactic value (NH=4.5x10^20 cm^-2) and\nadding a neutral, redshifted absorber component to the spectral model.\nWith a simple F-test we evaluate the chance occurrence probability of\nthe improvement to be of 2.6x10^-4. Such model yields an intrinsic\nNH>3x10^21 and a redshift z>1 (90% confidence level for 2 parameters\nof interest). However, neither the intrinsic column density nor the\nredshift are well constrained towards large values, owing to the lack\nof absorption edges in the spectrum.\nThe resulting power law photon index is Gamma=2.01+/-0.05.\nThe observed flux is of 5.2x10^-13 erg cm^-2 s^-1 in 0.2-10 keV;\nthe corresponding unabsorbed flux is of 7.4x10^-13 erg cm^-2 s^-1.\n\nFinally, we divided the dataset into two time intervals of ~15900 s and\n~27600 s (each containing about half of the counts from the afterglow)\nand we repeated the spectral analysis. We found no significant spectral\nchanges in the two considered intervals.\n\nThis message may be cited.",
  "circularId": 3293,
  "createdOn": 1113914748000,
  "email": "deluca@mi.iasf.cnr.it",
  "subject": "GRB050326: analysis of the XMM-Newton observation",
  "submitter": "Andrea De Luca at IASF-CNR,Milano  <deluca@mi.iasf.cnr.it>",
  "eventId": "GRB 050326"
}