Aims. Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods. The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results. The catalogue, the largest ever made at X-ray wavelengths, contains 246 897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191 870 unique sources. The catalogue fields cover a sky area of more than 500 deg 2 . The non-overlapping sky area is ∼360 deg 2 (∼1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties

The XIS is an X-ray Imaging Spectrometer system, consisting of state-of-the-art charge-coupled devices (CCDs) optimized for X-ray detection, camera bodies, and control electronics. Four sets of XIS sensors are placed at the focal planes of the grazing-incidence, nested thin-foil mirrors (XRT: X-Ray Telescope) onboard the Suzaku satellite. Three of the XIS sensors have front-illuminated CCDs, while the other has a back-illuminated CCD. Coupled with the XRT, the energy range of 0.2-12 keV with energy resolution of 130 eV at 5.9 keV, and a field of view of 18 × 18 are realized. Since the Suzaku launch on 2005 July 10, the XIS has been functioning well.

Context. Our Galaxy hosts at its dynamical center Sgr A*, the closest supermassive black hole. Surprisingly, its luminosity is several orders of magnitude lower than the Eddington luminosity. However, the recent observations of occasional rapid X-ray flares from Sgr A* provide constraints on the accretion and radiation mechanisms at work close to its event horizon. Aims. Our aim is to investigate the flaring activity of Sgr A* and to constrain the physical properties of the X-ray flares. Methods. In Spring 2007, we observed Sgr A* with XMM-Newton with a total exposure of ∼230 ks. We have performed timing and spectral analysis of the new X-ray flares detected during this campaign. To study the range of flare spectral properties, in a consistent manner, we have also reprocessed, using the same analysis procedure and the latest calibration, archived XMM-Newton data of previously reported rapid flares. The dust scattering was taken into account during the spectral fitting. We also used Chandra archived observations of the quiescent state of Sgr A* for comparison. Results. On April 4, 2007, we observed for the first time within a time interval of roughly half a day, an enhanced incidence rate of X-ray flaring, with a bright flare followed by three flares of more moderate amplitude. The former event represents the second brightest X-ray flare from Sgr A* on record with a peak amplitude of about 100 above the quiescent luminosity. This new bright flare exhibits similar light-curve shape (nearly symmetrical), duration (∼3 ks) and spectral characteristics to the very bright flare observed in ), are compatible within the error bars with those of the bright flares. The column density found, for a power-law model taking into account the dust scattering, during the flares is at least two times higher than the value expected from the (dust) visual extinction toward Sgr A* (A V ∼ 25 mag), i.e., 4.5 × 10 22 cm −2 . However, our fitting of the Sgr A* quiescent spectra obtained with Chandra, for a power-law model taking into account the dust scattering, shows that an excess of column density is already present during the non-flaring phase. Conclusions. The two brightest X-ray flares observed so far from Sgr A* exhibited similar soft spectra.

We present results of optical identiÐcation of the X-ray sources detected in the ASCA Large Sky Survey. Optical spectroscopic observations were done for 34 X-ray sources that were detected with the SIS in the 2È7 keV band above 3.5 p. The Ñux limit corresponds to D1 ] 10~13 ergs cm~2 s~1 in the 2È10 keV band. The sources are identiÐed with 30 active galactic nuclei (AGNs), two clusters of galaxies, and one Galactic star. Only one source is still unidentiÐed.All of the X-ray sources that have a hard X-ray spectrum with an apparent photon index of smaller than 1 in the 0.7È10 keV band are identiÐed with narrow-line or weak-broad-line AGNs at redshifts smaller than 0.5. This fact supports the idea that absorbed X-ray spectra of narrow-line and weak-broadline AGNs make the cosmic X-ray background (CXB) spectrum harder in the hard X-ray band than that of a broad-line AGN, which is the main contributor in the soft X-ray band. Assuming their intrinsic spectra are same as a broad-line AGN (a power-law model with a photon index of 1.7), their X-ray spectra are Ðtted with hydrogen column densities of at the objectÏs redshift. On log N H (cm~2) \ 22È23 the other hand, X-ray spectra of the other AGNs are consistent with that of a nearby type 1 Seyfert galaxy. In the sample, four high-redshift luminous broad-line AGNs show a hard X-ray spectrum with an apparent photon index of 1.3^0.3. The hardness may be explained by the reÑection component of a type 1 Seyfert galaxy. The hard X-ray spectra may also be explained by absorption with at the objectÏs redshift, if we assume an intrinsic photon index of 1.7. The origin log N H (cm~2) \ 22È23 of the hardness is not clear yet.Based on the log NÈlog S relations of each population, contributions to the CXB in the 2È10 keV band are estimated to be 9% for less-absorbed AGNs including the four high-(log N H (cm~2) \ 22) redshift broad-line AGNs with a hard X-ray spectrum, 4% for absorbed AGNs (22 \ log N H (cm~2) \ 23, without the four hard broad-line AGNs), and 1% for clusters of galaxies in the Ñux range from 3 ] 10~11 ergs cm~2 s~1 to 2 ] 10~13 ergs cm~2 s~1. If the four hard broad-line AGNs are included in the absorbed AGNs, the contribution of the absorbed AGNs to the CXB is estimated to be 6%.In optical spectra, there is no high-redshift luminous cousin of a narrow-line AGN in our sample. The redshift distribution of the absorbed AGNs is limited below z \ 0.5 excluding the four hard broad-line AGNs, in contrast to the existence of 15 less-absorbed AGNs above z \ 0.5. The redshift distribution of the absorbed AGNs suggests a deÐciency of AGNs with column densities of in log N H (cm~2) \ 22È23 the redshift range 0.5È2, or in the X-ray luminosity range larger than 1044 ergs s~1, or both. If the large column densities of the four hard broad-line AGNs are real, they could complement the deÐciency of X-ray absorbed luminous high-redshift AGNs.