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Aims.We present the first X-ray observations with the XMM-Newton and INTEGRAL satellites of the recently discovered cataclysmic variable 1RXS J173021.5-055933, together with simultaneous UV and coordinated optical photometry aiming at characterising its broad-band temporal and spectral properties and classifying this system as a magnetic one.

Context.Following an extensive survey of the galactic plane by the INTEGRAL satellite, new hard X-ray sources are discovered with a significant fraction of Cataclysmic Variables (CVs) among them.

Aims.HETE J1900.1–2455 is the seventh known X-ray transient accreting millisecond pulsar and has been in outburst for more than one year. We compared the data on HETE J1900.1–2455 with other similar objects and made an attempt at deriving constraints on the physical processes responsible for a spectral formation.

Aims.XMM-Newton observations to determine for the first time the broad-band X-ray properties of the faint, high galactic latitude intermediate polar UU Col are presented.

We present the first time resolved medium resolution optical spectroscopy of the recently identified peculiar Intermediate Polar (IP) 1RXS J154814.5-452845, which allows us to precisely determine the binary orbital period ($P_{\Omega}=9.87$±0.03 h) and the white dwarf spin period ($P_{\omega}=693.01$±0.06 s). This system is then the third just outside the purported ~6–10 h IP orbital period gap and the fifth of the small group of long period IPs, which has a relatively high degree of asynchronism. From the presence of weak red absorption features, we identify the secondary star with a spectral type K2 ±2 V, which appears to have evolved on the nuclear timescale. From the orbital radial velocities of emission and the red absorption lines a mass ratio $q=0.65$±0.12 is found. The masses of the components are estimated to be $M_{{\rm WD}} \geq 0.5~M_{\odot}$and $M_{{\rm sec}}=0.4{-}0.79~M_{\odot}$and the binary inclination $25^\circ < i \leq 58^\circ$. A distance between 540–840 pc is estimated. At this distance, the presence of peculiar absorption features surrounding Balmer emissions cannot be due to the contribution of the white dwarf photosphere and their spin modulation suggests an origin in the magnetically confined accretion flow. The white dwarf is also not accreting at a particularly high rate ($\dot M < 5$$\times$$10^{16}~{\rm g~s}^{-1}$), for its orbital period. The spin-to-orbit period ratio $P_{\omega}/P_{\Omega}$= 0.02 and the low mass accretion rate suggest that this system is far from spin equilibrium. The magnetic moment of the accreting white dwarf is found to be $\mu < 4.1$$\times$1032G cm3, indicating a low magnetic field system.

We report the first time-resolved photometric and spectroscopic optical observations of the X-ray source RX J2133.7+5107, identified in the ROSAT survey. A clear persistent optical light pulsation is discovered with fast photometry at a period of $P_{\omega}=(570.823\pm0.013)$s which we associate with the spin period of an accreting white dwarf. Radial velocity curves of the strong emission lines show modulation with a period of $P_{\Omega}=(7.193\pm0.016)$h, identified as the orbital period. These observations establish that the source is a member of the intermediate polar class (IPs) of magnetic cataclysmic variables. With only 4 IPs with longer orbital periods, RX J2133.7+5107  is among the widest systems. It is a unique IP with an orbital period in the middle of the so-called (6-10) h IP gap and it shows a significant degree of asynchronism with a ratio $P_{\omega}$/$P_{\Omega}$of 0.02. When attributed to the motion of the white dwarf, the emission lines orbital modulation yields a mass function of $f_{\rm m} = (1.05\pm 0.21)\times 10^{-2}$$M_{\odot}\,$which, for a probable inclination $i \leq 45^{\circ}$and a white dwarf mass $M_{\rm wd} = (0.6{-}1.0)~M_{\odot}$, corresponds to a secondary mass $M_{\rm s} \geq (0.27{-}0.37)$$M_{\odot}\,$.

We present the hard X-ray time-averaged spectrum of the intermediate polar V709 Cas observed with INTEGRAL. We performed the observation using data from the IBIS/ISGRI instrument in the 20–100 keV energy band and from JEM-X at lower energy (5–20 keV). Using different multi-temperature and density X-ray post-shock models we measured an improved post-shock temperature of ~40 keV and estimated the V709 Cas mass to be 0.82$^{+0.12}_{-0.25}$$M_{\odot}$. We compare the resulting spectral parameters with previously reported BeppoSAX and RXTEobservations.

We report on the first pointed X-ray observations with XMM-Newtonand RXTEsatellites of the X-ray source RX J0757.0+6306 = HT Cam. We detect a strong 515 s X-ray modulation confirming the optical photometric period found in 1998, which definitively assigns this source to the intermediate polar class of magnetic cataclysmic variables. The lack of orbital sidebands in the X-rays indicates that the X-ray period is the spin period of the accreting white dwarf. Simultaneous ultraviolet and optical B-band photometry acquired with the XMM-Newton Optical Monitor and coordinated optical UBVRIphotometric data acquired at the Nordic Optical Telescope (La Palma) show that the optical pulse is in phase with the X-rays and hence originates in the magnetically-confined accretion flow. The lack of ultraviolet spin modulation suggests that accretion-induced heating on the white dwarf surface is not important in this source. Spectral analyses of XMM-Newton EPIC and RGS data show that HT Cam has a multi-temperature spectrum and, contrary to most intermediate polars, it does not suffer from strong absorption. With its 86 min orbital period, HT Cam is the third confirmed system of this class below the 2–3 h period gap accreting at a low rate.

Two recent INTEGRALpapers report a timing and spectral analysis of the transient Be/X-ray pulsar SAX J2103.5+4545 at high energies (5–200 keV). In this work we present for the first time a study of the pulse profile at energies above 20 keV using INTEGRALdata. The spin-pulse profile shows a prominent (with a duty cycle of 14%) and broad (with a FWHMof ~51 s) peak and a secondary peak which becomes more evident above 20 keV. The pulsed fraction increases with energy from ~45% at 5–40 keV to ~80% at 40–80 keV. The morphology of the pulse profile also changes as a function of energy, consistent with variations in the spectral components that are visible in the pulse phase resolved spectra. A study of the double peaked profile shows that the difference in the two peaks can be modeled by a different scattering fraction between the radiation from the two magnetic poles.

We report on preliminary results of IBIS/ISGRI serendipitous observations of Cygnus X-3 in the 15–100 keV energy range during the INTEGRAL Performance and Verification phase. This peculiar microquasar was inside IBIS/ISGRI field of view at a ~9° distance from the pointing direction during Cygnus X-1 staring observations in November and December 2002. We analyzed observations from 27 November 2002 to 8 December 2002 with an effective on source exposure time of ~300 ks. Cyg X-3 was always significantly detected in the 15–40 and 40–100 keV energy bands during single exposures lasting between 30 min and one hour. The source light curve shows the characteristic 4.8-hour modulation with a shape consistent with a standard template. The two light curves' phase zero have no measurable offset and their values are consistent with historical ephemeris. These results show that even at this early stage of the mission, IBIS/ISGRI is capable of producing high quality scientific results on highly off axis, relatively bright targets.

We report on the first far-UV observations of the asynchronous polar BY Cam made by the Far-Ultraviolet Spectroscopic Explorer (FUSE). The source is known to exhibit the most extreme NV/CIV emission resonance line ratio observed among polars. The FUSE observations reveal a OVI resonance line weaker than in the prototype of polars, AM Her, with the absence of a detectable narrow component. The OVI broad line is detected with an equivalent width of the same order as in AM Her, the blueward doublet component is clearly present but the redward component is strongly affected by H2absorption. The presence of a strong NIII line and weak CIII lines also confirms the peculiar CNO line flux. We compare the resonance CNO line intensities with the predictions of the CLOUDY plasma code coupled to a geometrical model of the accretion column. Varying the temperature and/or intensity of the ionising spectrum is unable to reproduce the observed broad line ratios. A solution is obtained by significantly altering the element abundances with a strong depletion of C, overabundance of N and a weak underabundance of O. This confirms previous suggestions of non-solar abundances which may result from redistribution in the accreted material following nova outbursts and/or the secondary nuclear evolution. A very significant H2absorption is observed in front of the source, a possible indication for either the existence of a dense interstellar cloud or of circumstellar material.

We present the last pointed observation of AM Her carried out during the life of the BeppoSAX satellite. It was bright at the beginning of the observation, but dropped to the lowest X-ray level ever observed so far. The X-ray emission during the bright period is consistent with accretion occurring onto the main pole of the magnetized white dwarf. The rapid change from the active stateto the low deep state indicates a drop by a factor of 17 in the accretion rate and hence that accretion switched-off. The short timescale (less than one hour) of this variation still remains a puzzle. Optical photometry acquired simultaneousy during the low state shows that the white dwarf remains heated, although a weak emission from the accretion stream could be still present. Cyclotron radiation, usually dominating the Vand Rbands, is negligible thus corroborating the possibility that AM Her was in an off-accretion state. The X-ray emission during the inactive state is consistent with coronal emission from the secondary late type star.

We present RXTE and BeppoSAX observations of the Intermediate Polar V 709 Cas acquired in 1997 and 1998 respectively. The X-ray emission from 0.1 to 30 keV is dominated by the strong pulsation at the rotational period of the white dwarf (312.8 s) with no sign of orbital or sideband periodicity, thus confirming previous ROSAT results. However, we detect changes in the power spectra between the two epochs. While the second harmonic of the spin period is present during both observations, the first harmonic is absent in 1997. An increase in the amplitude of the spin pulsation is found between 1997 and 1998 together with a decrease in the X-ray flux. The average X-ray spectrum from 0.1 to 100 keV is well described by an isothermal plasma at ~27 keV plus complex absorption and an iron Kαfluorescent line, due to reflection from the white dwarf surface. The rotational pulsation is compatible with complex absorption dominating the low energy range, while the high energy spin modulation can be attributed to tall shocks above the accreting poles. The RXTE spectrum in 1997 also shows the presence of an absorption edge from ionized iron likely located in the pre-shock accretion flow. The variations along the spin period of the partial covering absorber and of reflection are compatible with the classical accretion curtain scenario. The variations in the spin pulse characteristics and X-ray flux indicate that V 709 Cas experiences changes in the mass accretion rate on timescales from months to years.

Results are presented from the first detailed spectroscopic observations of the recently identified intermediate polar RX J0028.8+5917/V709 Cas. The study of the emission line radial velocities allows us to remove the uncertainties on the different aliases of the orbital period and a best value is found at (0.2225$ \pm $0.0002) day. It is also found that the system shows significant $EW\sim$(2-4) Åbroad absorptions affecting the Balmer lines from H$_{\delta}$to H$_{\beta}$. These broad absorptions are interpreted as the contribution of an underlying white dwarf atmosphere. The characteristics of the absorptions are found to be consistent with a DA log g= 8 white dwarf at a temperature of ~23 000 K, contributing ~17% (at 4500 Å) to the overall flux. This is the first direct detection of a white dwarf in an intermediate polar system. The absence of significant Zeeman splitting indicates a magnetic field lower than 10 MG, confirming that, at least in some cases, intermediate polars have weaker fields than polars. Different possibilities are discussed to explain the substantial contribution of the white dwarf to the overall flux.

The bright eclipsing and bursting low-mass X-ray binary EXO 0748-676 has been observed at several occasions by XMM-Newtonduring the initial calibration and performance verification (CAL/PV) phase. We present here the results obtained from observations with the EPIC cameras. Apart from several type-I X-ray bursts, the source shows a high degree of variability with the presence of soft flares. The wide energy coverage and high sensitivity of XMM-Newtonallows for the first time a detailed description of the spectral variability. The source is found to be the superposition of a central (~2 108cm) Comptonized emission, most probably a corona surrounding the inner edge of an accretion disk, associated with a more extended (~3 1010cm) thermal halo at a typical temperature of ~0.6 keV with an indication of non-solar abundances. Most of the variations of the source can be accounted for by a variable absorption affecting only the central comptonized component and reaching up to NH$\sim 1.3 10^{23}$cm-2. The characteristics of the surrounding halo are found compatible with an irradiated atmosphere of an accretion disc which intercepts the central emission due to the system high inclination.

XMM-Newtonobservations of the Crab provide new information on its integrated X-ray spectrum and the variation of the spectral form across the nebula. The Crab pulsar and its surrounding torus exhibit the hardest spectra with power-law indices of $\Gamma = 1.6$and 1.8. The jet and outer reaches of the nebula are significantly softer with $\Gamma = 2.1$and 2.3 respectively. For the whole nebula, the huge number of recorded counts allows a detailed examination of the soft X-ray absorption due to cool gas in the foreground of the Crab. Absorption edges due to oxygen and neon are clearly identified. Oxygen and iron in the interstellar medium are underabundant by a factor of $0.63 \pm 0.01$. The average $N_{\rm H}=3.45\pm0.02 10^{21}$cm-2and varies by less than $\pm11\%$on a scale equal to or larger than 20 arcsec over the face of the nebula. These observations of the Crab provide an excellent demonstration of the power of the EPIC cameras on XMM-Newtonfor spatial, spectral and timing studies.

Context. A significant number of cataclysmic variables have been detected as hard X-ray sources in the INTEGRAL survey, most of them of the magnetic intermediate polar type.Aims. We present a detailed X-ray broad-band study of two new sources, IGR?J00234+6141 and 1RXS?J213344.1+510725, that allow us to classify them as secure members of the intermediate polar class.Methods. Timing and spectral analysis of IGR?J00234+6141 are based on an XMM-Newton observation and INTEGRAL publicly available data. For 1RXS?J213344.1+510725, we use XMM-Newton and Suzaku observations at different epochs, as well as INTEGRAL publicly available data.Results. We determine a spin period of 561.64?? 0.56?s for the white dwarf in IGR?J00234+6141. The X-ray pulses are observed up to ?2?keV. From XMM-Newton and Suzaku observations of 1RXS?J213344.1+510725, we find a rotational period of 570.862?? 0.034?s. The observations span three epochs where the pulsation is observed to change at different energies both in amplitude and shape. In both objects, the spectral analysis spanned over a wide energy range, from 0.3 to 100?keV, shows the presence of multiple emission components absorbed by dense material. The X-ray spectrum of IGR?J00234+6141 is consistent with a multi-temperature plasma with a maximum temperature of ?50?keV. In 1RXS?J213344.1+510725, multiple optically thin components are inferred, as well as an optically thick (blackbody) soft X-ray emission with a temperature of ?100?eV. This adds 1RXS?J213344.1+510725 to the growing group of soft X-ray intermediate polars.Conclusions. Though showing similar rotational periods and being hard X-ray sources, these two intermediate polars appear different in several respects, among which the presence of a soft X-ray component in 1RXS?J213344.1+510725. This source also emits circularly polarized light in the optical band, thus joining the group of soft and polarized intermediate polars as a fifth member. How the hard X-ray and polarized emission are thermalized in these systems is a timely question.

Aims. We analyze the first X-ray observations with XMM-Newton of 1RXS?J070407.9+262501 and 1RXS?180340.0+401214, in order to characterize their broad-band temporal and spectral properties, also in the UV/optical domain, and to confirm them as intermediate polars.Methods. For both objects, we performed a timing analysis of the X-ray and UV/optical light curves to detect the white dwarf spin pulsations and study their energy dependence. For 1RXS?180340.0+401214 we also analyzed optical spectroscopic data to determine the orbital period. X-ray spectra were analyzed in the 0.2?10.0?keV range to characterize the emission properties of both sources.Results. We find that the X-ray light curves of both systems are energy dependent and are dominated, below 3?5?keV, by strong pulsations at the white dwarf rotational periods (480?s for 1RXS?J070407.9+262501 and 1520.5?s for 1RXS?180340.0+401214). In 1RXS?180340.0+401214 we also detect an X-ray beat variability at 1697?s which, together with our new optical spectroscopy, favours an orbital period of 4.4?h that is longer than previously estimated. Both systems show complex spectra with a hard (temperature up to 40?keV) optically thin and a soft (kT ~ 85?100?eV) optically thick components heavily absorbed by material partially covering the X-ray sources.Conclusions. Our observations confirm the two systems as intermediate polars and also add them as new members of the growing group of ?soft? systems which show the presence of a soft X-ray blackbody component. Differences in the temperatures of the blackbodies are qualitatively explained in terms of reprocessing over different sizes of the white dwarf spot. We suggest that systems showing cooler soft X-ray blackbody components also possess white dwarfs irradiated by cyclotron radiation.

Context. Sirius is the brightest star in the sky and a strong source of diffuse light for modern telescopes so that the immediate surroundings of the star are still poorly known.Aims. We study the close surroundings of the star (2 to 25??) by means of adaptive optics and coronographic device in the near-infrared, using the ESO/ADONIS system. Methods. The resulting high contrast images in the JHKs bands have a resolution of ~0.2??? and limiting apparent magnitude ranging from mK=9.5 at 3??? from Sirius-A to mK=13.1 at 10??. These are the first and deepest images of the Sirius system in this infrared range.Results. From these observations, accurate infrared photometry of the Sirius-B white dwarf companion is obtained. The JH magnitudes of Sirius-B are found to agree with expectations for a DA white dwarf of temperature (T=25000?K) and gravity (log g = 8.5), consistent with the characteristics determined from optical observations. However, a small, significant excess is measurable for the K band, similar to that detected for ?dusty? isolated white dwarfs harbouring suspected planetary debris. The possible existence of such circumstellar material around Sirius-B has still to be confirmed by further observations.Conclusions. These deep images allow us to search for small but yet undetected companions to Sirius. Apart from Sirius-B, no other source is detected within the total 25??? field. A comparison of the flux expected from the faintest known brown dwarfs at the distance of Sirius demonstrates that the above limiting magnitudes correspond to a star of spectral type later than T5 at 5??? and T7 at 10??. Using theoretical spectra of brown dwarfs and planet-size objects, we also show that the end of the brown dwarf sequence is reached in the outer part of the image. The minimum detectable mass is around 10 MJupinside the planetary limit, indicating that an extrasolar planet at a projected distance of ~25?AU from Sirius would have been detected.

We present mid-infrared spectrophotometric results obtained with the ISO on the peculiar X-ray binary Cygnus X-3 in quiescence, at orbital phases 0.83 to 1.04. The 2.4–12 $\mu$m continuum radiation observed with ISOPHOT-S can be explained by thermal free-free emission in an expanding wind with, above 6.5 $\mu$m, a possible additional black-body component with temperature $T \sim 250$ K and radius $R \sim 5000$  $R_{\odot}$ at 10 kpc, likely due to thermal emission by circumstellar dust. The observed brightness and continuum spectrum closely match that of the Wolf-Rayet star WR 147, a WN8+B0.5 binary system, when rescaled at the same 10 kpc distance as Cygnus X-3. A rough mass loss estimate assuming a WN wind gives ~$1.2\,\times\, 10^{-4}$  ${M}_\odot$ yr$^{-1}$. A line at ~4.3 $\mu$m with a more than 4.3 $\sigma$ detection level, and with a dereddened flux of 126 mJy, is interpreted as the expected He I 3p–3s line at 4.295 $\mu$m, a prominent line in the WR 147 spectrum. These results are consistent with a Wolf-Rayet-like companion to the compact object in Cyg X-3 of WN8 type, a later type than suggested by earlier works.

Context. The nature of the hard X-ray source XSS J12270-4859 is still unclear. It was claimed to be a possible magnetic cataclysmic variable of the Intermediate Polar type from its optical spectrum and a possible 860 s X-ray periodicity in RXTEdata. However, recent observations do not support the latter variability, leaving this X-ray source still unclassified.Aims. To investigate its nature we present a broad-band X-ray and gamma ray study of this source based on a recent XMM-Newtonobservation and archival INTEGRALand RXTEdata. Using the Fermi/LAT 1-year point source catalogue, we tentatively associate XSS J12270-4859 with 1FGL J1227.9-4852, a source of high-energy gamma rays with emission up to 10 GeV. We further complement the study with UV photometry from XMM-Newtonand ground-based optical and near-IR photometry.Methods. We have analysed both timing and spectral properties in the gamma rays, X-rays, UV and optical/near-IR bands of XSS J12270-4859.Results. The X-ray emission is highly variable, showing flares and intensity dips. The flares consist of flare-dip pairs. Flares are detected in both X-rays and the UV range, while the subsequent dips are present only in the X-ray band. Further aperiodic dipping behaviour is observed during X-ray quiescence, but not in the UV. The broad-band 0.2–100 keV X-ray/soft gamma ray spectrum is featureless and well described by a power law model with Γ= 1.7. The high-energy spectrum from 100 MeV to 10 GeV is represented by a power law index of 2.45. The luminosity ratio between 0.1–100 GeV and 0.2–100 keV is ~0.8, indicating that the GeV emission is a significant component of the total energy output. Furthermore, the X-ray spectrum does not greatly change during flares, quiescence and the dips seen in quiescence. The X-ray spectrum however hardens during the post-flare dips, where a partial covering absorber is also required to fit the spectrum. Optical photometry acquired at different epochs reveals a period of 4.32 hr that could be ascribed to the binary orbital period. Near-IR, possibly ellipsoidal, variations are detected. Large amplitude variability on shorter (tens mins) timescales is found to be non-periodic.Conclusions. The observed variability at all wavelengths together with the spectral characteristics strongly favour a low-mass atypical low-luminosity X-ray binary and are against a magnetic cataclysmic variable nature. The association with a Fermi/LAT high-energy gamma ray source further strengths this interpretation.

Context. The nature of the hard X-ray source XSS J12270-4859 is still unclear. It was claimed to be a possible magnetic cataclysmic variable of the Intermediate Polar type from its optical spectrum and a possible 860 s X-ray periodicity in RXTEdata. However, recent observations do not support the latter variability, leaving this X-ray source still unclassified.