XMM-NEWTON slew survey observations of the gravitational wave event GW150914

The detection of the first gravitational wave (GW) transient GW150914 prompted an extensive campaign of follow-up observations at all wavelengths. Although no dedicated XMM-Newton observations have been performed, the satellite passed through the GW150914 error region during normal operations. Here we report the analysis of the data taken during these satellite slews performed two hours and two weeks after the GW event. Our data cover 1.1 and 4.8 deg2 of the final GW localization region. No X-ray counterpart to GW150914 is found down to a sensitivity of 6 × 10−13 erg cm−2 s−1 in the 0.2–2 keV band. Nevertheless, these observations show the great potential of XMM-Newton slew observations for searching for the electromagnetic counterparts of GW events. A series of adjacent slews performed in response to a GW trigger would take lesssim1.5 days to cover most of the typical GW credible region. We discuss this scenario and its prospects for detecting the X-ray counterpart of future GW detections

The central region of M 31 observed with XMM-Newton. I. Group properties and diffuse emission

We present the results of a study based on an XMM-Newton Performance Verification observation of the central 30´of the nearby spiral galaxy M 31. In the 34-ks European Photon Imaging Camera (EPIC) exposure, we detect 116 sources down to a limiting luminosity of #1 10#2 erg s-1 (0.3-12 keV, d=760 kpc). The luminosity distribution of the sources detected with XMM-Newton flattens at luminosities below $\sim$ 2.5 1037 erg s-1 . We make use of hardness ratios for the detected sources in order to distinguish between classes of objects such as super-soft sources and intrinsically hard or highly absorbed sources. We demonstrate that the spectrum of the unresolved emission in the bulge of M 31 contains a soft excess which can be fitted with a $\sim$0.35-keV optically-thin thermal-plasma component clearly distinct from the composite point-source spectrum. We suggest that this may represent diffuse gas in the centre of M 31, and we illustrate its extent in a wavelet-deconvolved image

Swift and XMM-Newton observations of the dark GRB 050326

We present Swift and XMM-Newton observations of the bright gamma-ray burst GRB050326, detected by the Swift Burst Alert Telescope. The Swift X-Ray Telescope (XRT) and XMM-Newton discovered the X-ray afterglow beginning 54 min and 8.5 h after the burst, respectively. The prompt GRB050326 fluence was (7.7 ± 0.9) × 10−6 erg cm−2 (20–150 keV), and its spectrum was hard, with a power law photon index Γ = 1.25 ± 0.03. The X-ray afterglow was quite bright, with a flux of 7 × 10−11 erg cm−2 s−1 (0.3–8 keV), 1 h after the burst. Its light curve did not show any break nor flares between ~1 h and ~6 d after the burst, and decayed with a slope α = 1.70 ± 0.05. The afterglow spectrum is well fitted by a power-law model, suffering absorption both in the Milky Way and in the host galaxy. The rest-frame hydrogen column density is significant, NH,z >~4 × 1021 cm−2, and the redshift of the absorber was constrained to be z > 1.5. There was good agreement between the spatial, temporal, and spectral parameters as derived by Swift-XRT and XMM-Newton. By comparing the prompt and afterglow fluxes, we found that an early break probably occurred before the beginning of the XRT observation, similarly to many other cases observed by Swift. However, the properties of the GRB050326 afterglow are well described by a spherical fireball expanding in a uniform external medium, so a further steepening is expected at later times. The lack of such a break allowed us to constrain the jet half-opening angle ϑj >~7◦. Using the redshift constraints provided by the X-ray analysis, we also estimated that the beaming-corrected gamma-ray energy was larger than 3 × 1051 erg, at the high end of GRB energies. Despite the brightness in X rays, only deep limits could be placed by Swift-UVOT at optical and ultraviolet wavelengths. Thus, this GRB was a “truly dark” event, with the optical-to-X-ray spectrum violating the synchrotron limit. The optical and X-ray observations are therefore consistent either with an absorbed event or with a high-redshift one. To obey the Ghirlanda relation, a moderate/large redshift z >~ 4.5 is required