GCN Circular 5469
Sergio Campana (OAB) & Andrea De Luca (IASF Mi) on behalf of a larger collaboration report: We have analyzed the data from the XMM-Newton observation of GRB060729, discovered by Swift on 2006, Jul 29, 19:12:29 UT (Grupe et al., GCN5365). The XMM-Newton observation started on 2006, July 30 07:59 UT and lasted for ~61 ks. A high particle background level affects only mildly the whole observation and only the highest flares have been cut out, in consideration also of the source strength. The background subtracted pn light curve (0.3-10 keV) shows a clear decay from about 5 c/s at the beginning of the observation down to 2 c/s. The light curve can be fit with a power law decay with index delta=1.04+/-0.02 but with a large chi2=1.8 (58 dof). This is due to a large bump in the middle of the exposure. Adding a Gaussian we obtain a better chi2=0.7 (55 dof). The central time is 69+/-1 ks (90% confidence) from the burst start and the (Gaussian) width over the time is about 7+/-2%. We note also that the time of the XMM-Newton observation is close to the break time observed by Swift XRT in the GRB060729 light curve (Grupe, GCN5432). Fitting a broken power law to we obtain a first decay index delta1=0.85+/-0.05, which is inconsistent with the early slope of 0.34 reported by Grupe. We extracted time-averaged spectra from the EPIC pn camera (since in the initial part of the MOS observation the GRB spectrum should be mildly piled-up) and the two RGS spectrometers (first and second order) and we generated ad-hoc response files. A simultaneous fit with an absorbed power law model with Galactic and intrinsic (at a redshift of z=0.54, Thoene et al. GCN5373) yields a reduced chi2 of 1.05 (1824 dof, without any systematic error). The resulting NH=(3.9+/-0.9)x1020 cm-2 (consistent with the Galactic value of NH=4.8x1020 cm-2, Dickey & Lockman 1990) and a relatively low NH_host=(9.2+/-0.4)x1020 cm-2. The best fitting power law photon index is Gamma=2.09+/-0.01. The RGS spectrometers do now show any clear evidence of absorption or emission lines in the 0.3-2 keV energy range. The observed flux is of 9.5x10-12 erg cm-2 s-1 in 0.3-10 keV; the corresponding unabsorbed flux is of 1.2x10-11 erg cm-2 s-1. This message may be cited.