F. Haberl

The European Photon Imaging Camera on XMM-Newton: The pn-CCD camera

The European Photon Imaging Camera (EPIC) consortium has provided the focal plane instruments for the three X-ray mirror systems on XMM-Newton. Two cameras with a reflecting grating spectrometer in the optical path are equipped with MOS type CCDs as focal plane detectors (Turner 2001), the telescope with the full photon flux operates the novel pn-CCD as an imaging X-ray spectrometer. The pn-CCD camera system was developed under the leadership of the Max-Planck-Institut fur extraterrestrische Physik (MPE), Garching. The concept of the pn-CCD is described as well as the dierent operational modes of the camera system. The electrical, mechanical and thermal design of the focal plane and camera is briefly treated. The in-orbit performance is described in terms of energy resolution, quantum eciency, time resolution, long term stability and charged particle background. Special emphasis is given to the radiation hardening of the devices and the measured and expected degradation due to radiation damage of ionizing particles in the rst 9 months of in orbit operation.

The ROSAT all - sky survey bright source catalogue

In order to ensure the quality of the source catalogue derived from the SASS processing an automatic as well as a visual screening procedure was applied to 1378 survey fields. Most (94%) of the 18,811 sources were confirmed by this screening process. The rest is flagged for various reasons. Broad band images are available for a subset of the flagged sources. Details of the screening process can be found at www.rosat.mpe-garching.mpg.de/survey/rass-bsc/doc.html.

The XMM-Newton view of stellar coronae: X-ray spectroscopy of the corona of AB Doradus

M. A. acknowledges support from the Swiss National Science Foundation (grants 2100-049343 and 2000-058827), from the Swiss Academy of Sciences, and from the Swiss Commission for Space Research. H. M., K. B, and J. P. acknowledge financial support from PPARC. A. M. and R. P. acknowledge support from the Italian Space Agency. SRON is supported financially by NWO.

An accreting pulsar with extreme properties drives an ultraluminous x-ray source in NGC 5907

Spinning up an extragalactic neutron star Ultraluminous x-ray sources (ULXs) are strange objects in other galaxies that cannot be explained by conventional accretion onto stellar-mass objects. This has led to exotic interpretations, such as the long-sought intermediate-mass black holes. Israel et al. observed a ULX in the nearby galaxy NGC 5907 and found that it is instead a neutron star. The spinning neutron star is accreting material so fast that its spin period is quickly accelerating. The only way that it can consume enough material to explain these properties is if it has a strong multipolar magnetic field. Science, this issue p. 817 An ultraluminous x-ray source in NGC 5907 is a spinning neutron star with a complex magnetic field. Ultraluminous x-ray sources (ULXs) in nearby galaxies shine brighter than any x-ray source in our Galaxy. ULXs are usually modeled as stellar-mass black holes (BHs) accreting at very high rates or intermediate-mass BHs. We present observations showing that NGC 5907 ULX is instead an x-ray accreting neutron star (NS) with a spin period evolving from 1.43 seconds in 2003 to 1.13 seconds in 2014. It has an isotropic peak luminosity of ~1000 times the Eddington limit for a NS at 17.1 megaparsec. Standard accretion models fail to explain its luminosity, even assuming beamed emission, but a strong multipolar magnetic field can describe its properties. These findings suggest that other extreme ULXs (x-ray luminosity ≥ 1041 erg second−1) might harbor NSs.

Bright radio emission from an ultraluminous stellar-mass microquasar in M 31

A subset of ultraluminous X-ray sources (those with luminosities of less than 1040 erg s−1; ref. 1) are thought to be powered by the accretion of gas onto black holes with masses of ∼5–20, probably by means of an accretion disk. The X-ray and radio emission are coupled in such Galactic sources; the radio emission originates in a relativistic jet thought to be launched from the innermost regions near the black hole, with the most powerful emission occurring when the rate of infalling matter approaches a theoretical maximum (the Eddington limit). Only four such maximal sources are known in the Milky Way, and the absorption of soft X-rays in the interstellar medium hinders the determination of the causal sequence of events that leads to the ejection of the jet. Here we report radio and X-ray observations of a bright new X-ray source in the nearby galaxy M 31, whose peak luminosity exceeded 1039 erg s−1. The radio luminosity is extremely high and shows variability on a timescale of tens of minutes, arguing that the source is highly compact and powered by accretion close to the Eddington limit onto a black hole of stellar mass. Continued radio and X-ray monitoring of such sources should reveal the causal relationship between the accretion flow and the powerful jet emission.

The proper motion and energy distribution of the isolated neutron star RX J0720.4-3125

ESO 4 m class telescope and VLT deep imaging of the isolated neutron star RX J0720.4-3125 reveals a proper motion of µ = 97 ± 12 mas/yr and a blue U − B color index. We show that a neutron star atmosphere model modified to account for a limited amount of hydrogen on the stars surface can well represent both the optical and X-ray data without invoking any additional thermal component. The large proper motion almost completely excludes the possibility that accretion from the interstellar medium is the powering mechanism of the X-ray emission. It also implies that the proposed spin down is entirely due to magnetic dipole losses. RX J0720.4-3125 is thus very likely a middle aged cooling neutron star. Its overall properties are quite similar to some of the long period radio pulsars recently discovered, giving further support to the idea that RX J0720.4-3125 may be a pulsar whose narrow radio beam does not cross the Earth.

A ROSAT PSPC catalogue of X-ray sources in the SMC region ?

We present a catalogue of 517 discrete X-ray sources in a 66 eld covering the Small Magellanic Cloud (SMC). The catalogue was derived from the pointed ROSAT PSPC observations performed between October 1991 and May 1994 and is complementary to the Large Magellanic Cloud (LMC) catalogue published by Haberl & Pietsch (1999). We followed the same identication scheme and used, among other information, X-ray hardness ratios and spatial extent to classify unknown sources as candi- dates for active galactic nuclei (AGN), foreground stars, supernova remnants (SNRs), supersoft sources (SSSs) and X-ray binaries. For 158 sources a likely source type is given, from which 46 sources are suggested as background AGN (including candidates resulting from a compari- son of X-ray and radio images). Nearly all of the X-ray binaries known in the SMC were detected in ROSAT PSPC observations; most of them with luminosities below 10 36 erg s 1 suggesting that the fraction of high luminos- ity X-ray binary systems in the Magellanic Clouds (MCs) is not signicantly larger than in our galaxy. Seventeen X-ray sources are associated with SNRs found in earlier work and we suggest here two additional extended sources as SNR candidates. Three very soft sources are newly clas- sied as SSSs from which one is identied with the sym- biotic star LIN 358 in the SMC.

X-ray observations of Be/X-ray binaries in the SMC

Fifteen Be/X-ray binaries and candidates in the SMC were observed serendipitously with the EPIC instruments of XMM-Newton during two observations of SNR 0047-73.5 and SNR 0103-72.6 in October 2000. A total of twelve of those sources are detected. For eleven of them an accurate position and in part detection of X-ray pulsations support the proposed identification as Be/X-ray binaries. In one case the improved X-ray position excludes the previously suggested identification with an Ha emission line star found within the ROSAT error circle. The detection of pulsations (172.2 s, 320.1 s and 751 s) from three hard X-ray sources with periods known from ASCA observations confirm their proposed identifications with ROSAT sources and their optical Be star counterparts. In addition, pulsations with a period of 263.6 s were found from XMMU J004723.7-731226 = RX J0047.3 -7312. For SAX J0103.2-7209 a pulse period of 341.2±0.5 s was determined, continuing the large spin-up seen with ASCA, BeppoSAX and Chandra between 1996 and 1999 with a period derivative of -1.6 s yr -1 covering now 4.5 years. The 0.3-10.0 keV EPIC spectra of all eleven Be/X-ray binaries and candidates are consistent with power-law energy distributions with derived photon indices strongly peaked at 1.00 with a standard deviation of 0.16. No pulsations are detected from RXJ0049.2-7311 and RXJ0049.5-7310 (both near the 9 s pulsar AX J0049-732) and RXJ0105,1-7211 (near AXJ0105-722, which may pulsate with 3.3 s), leaving the identification of the ASCA sources with ROSAT and corresponding XMM-Newton objects still unclear. We present an updated list of high-mass X-ray binaries (HMXBs) and candidates in the SMC incorporating improved X-ray positions obtained from Chandra and XMM-Newton observations. Including the results from this work and recent publications the SMC HMXB catalogue comprises 65 objects with at least 37 showing X-ray pulsations.

Discovery of a 0.42-s pulsar in the ultraluminous X-ray source NGC 7793 P13

NGC 7793 P13 is a variable (luminosity range ∼100) ultraluminous X-ray source proposed to host a stellar-mass black hole of less than 15 M⊙ in a binary system with orbital period of 64 d and a 18-23 M⊙ B9Ia companion. Within the EXTraS (Exploring the X-ray Transient and variable Sky) project, we discovered pulsations at a period of ∼0.42 s in two XMM-Newton observations of NGC 7793 P13, during which the source was detected at LX ∼ 2.1 × 1039 and 5 × 1039 erg s-1 (0.3-10 keV band). These findings unambiguously demonstrate that the compact object in NGC 7793 P13 is a neutron star accreting at super-Eddington rates. While standard accretion models face difficulties accounting for the pulsar X-ray luminosity, the presence of a multipolar magnetic field with B ∼ few × 1013 G close to the base of the accretion column appears to be in agreement with the properties of the system.

X-ray monitoring of optical novae in M 31 from July 2004 to February 2005

Context. Optical novae have recently been identified as the major class of supersoft X-ray sources in M 31 based on ROSAT and early XMM-Newton and Chandra  observations. Aims. This paper reports on a search for X-ray counterparts of optical novae in M 31 based on archival Chandra  HRC-I and ACIS-I as well as XMM-Newton observations of the galaxy center region obtained from July 2004 to February 2005. Methods. We systematically determine X-ray brightness or upper limit for counterparts of all known optical novae with outbursts between November 2003 to the end of the X-ray coverage. In addition, we determine the X-ray brightnesses for counterparts of four novae with earlier outbursts. Results. For comparison with the X-ray data we created a catalogue of optical novae in M 31 based on our own nova search programs and on all novae reported in the literature. We collected all known properties and named the novae consistently following the CBAT scheme. We detect eleven out of 34 novae within a year after the optical outburst in X-rays. While for eleven novae we detect the end of the supersoft source phase, seven novae are still bright more than 1200, 1600, 1950, 2650, 3100, 3370 and 3380 d after outburst. One nova is detected to turn on 50 d, another 200 d after outburst. Three novae unexpectedly showed short X-ray outbursts starting within 50 d after the optical outburst and lasting only two to three months. The X-ray emission of several of the novae can be characterized as supersoft from hardness ratios and/or X-ray spectra or by comparing HRC-I count rates with ACIS-I count rates or upper limits. Conclusions. The number of detected optical novae at supersoft X-rays is much higher than previously estimated (>