Ultraluminous X-ray sources are extragalactic objects located outside the nucleus of the host galaxy with bolometric luminosities exceeding 10(39) erg s(-1). These extreme luminosities-if the emission is isotropic and below the theoretical (Eddington) limit, where the radiation pressure is balanced by the gravitational pressure-imply the presence of an accreting black hole with a mass of approximately 10(2)-10(5) solar masses (M[symbol: see text]). The existence of such intermediate-mass black holes is in dispute, and though many candidates have been proposed, none are widely accepted as definitive. Here we report the detection of a variable X-ray source with a maximum 0.2-10 keV luminosity of up to 1.1 x 10(42) erg s(-1) in the edge-on spiral galaxy ESO 243-49, with an implied conservative lower limit for the mass of the black hole of approximately 500M[symbol: see text].

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 ultra-luminous X-ray (ULX) source ESO 243-49 HLX-1, which reaches a maximum luminosity of 10 42 erg s −1 (0.2-10 keV), currently provides the strongest evidence for the existence of intermediate mass black holes. To study the spectral variability of the source, we conduct an ongoing monitoring campaign with the Swift X-ray Telescope, which now spans more than two years. We found that HLX-1 showed two fast rise and exponential decay (FRED) type outbursts in the Swift XRT lightcurve with increases in the count rate of a factor ∼40 separated by 375±13 days. We obtained new XMM-Newton and Chandra dedicated pointings that were triggered at the lowest and highest luminosities, respectively. From spectral fitting, the unabsorbed luminosities ranged from 1.9×10 40 to 1.25×10 42 erg s −1 . We confirm here the detection of spectral state transitions from HLX-1 reminiscent of Galactic black hole binaries: at high luminosities, the X-ray spectrum showed a thermal state dominated by a disk component with temperatures of 0.26 keV at most, and at low luminosities the spectrum is dominated by a hard power law with a photon index in the range 1.4-2.1, consistent with a hard state. The source was also observed in a state consistent with the steep power law state, with a photon index of ∼ 3.5. In the thermal state, the luminosity of the disk component appears to scale with the fourth power of the inner disk temperature which supports the presence of an optically thick, geometrically thin accretion disk. The low fractional variability (rms of 9±9%) in this state also suggests the presence of a dominant disk. The spectral changes and long-term variability of the source cannot be explained by variations of the beaming angle and are not consistent with the source being in a super-Eddington accretion state as is proposed for most ULX sources with lower luminosities. All this indicates that HLX-1 is an unusual ULX as it is similar to Galactic black hole binaries, which have non-beamed and sub-Eddington emission, but with luminosities 3 orders of magnitude higher. In this picture, a lower limit on the mass of the black hole of >9000 M ⊙ can be derived, and the relatively low disk temperature in the thermal state also suggests the presence of an intermediate mass black hole of a few 10 3 M ⊙ .