arXiv subjects

A. Schwope

Publications and source records attributed to A. Schwope.

At least 73 records · Page 4Linked to original sources

arXiv2010

Cross-correlation of the 2XMMi catalogue with Data Release 7 of the Sloan Digital Sky Survey

The Survey Science Centre of the XMM-Newton satellite released the first incremental version of the 2XMM catalogue in August 2008 . With more than 220,000 X-ray sources, the 2XMMi was at that time the largest catalogue of X-ray sources ever published and thus constitutes an unprecedented resource for studying the high-energy properties of various classes of X-ray emitters such as AGN and stars. The advent of the 7th release of the Sloan Digital Sky Survey offers the opportunity to cross-match two major surveys and extend the spectral energy distribution of many 2XMMi sources towards the optical bands. We here present a cross-matching algorithm based on the classical likelihood ratio estimator. The method developed has the advantage of providing true probabilities of identifications without resorting to Monte-Carlo simulations. Over 30,000 2XMMi sources have SDSS counterparts with individual probabilities of identification higher than 90%. Using spectroscopic identifications from the SDSS DR7 catalogue supplemented by extraction from other catalogues, we build an identified sample from which the way the various classes of X-ray emitters gather in the multi dimensional parameter space can be analysed. We investigate two scientific use cases. In the first example we show how these multi-wavelength data can be used to search for new QSO2s. Although no specific range of observed properties allows us to identify Compton Thick QSO2s, we show that the prospects are much better for Compton Thin AGN2 and discuss several possible multi-parameter selection strategies. In a second example, we confirm the hardening of the mean X-ray spectrum with increasing X-ray luminosity on a sample of over 500 X-ray active stars and reveal that on average X-ray active M stars display bluer $g-r$ colour indexes than less active ones (abridged).

astro-ph.HE↗

arXiv2010

On the naming convention used for multiple star systems and extrasolar planets

The present naming convention for extrasolar planets used by the vast majority of researchers in the field is based upon an interpretation of the provisional I.A.U. standard for multiple star systems. With the existence of hundreds of exoplanets around single stars named by this convention and a handful of exoplanets around binary stars -- circumbinary planets -- it has become necessary to find a uniform and useful naming convention for the latter which is maximally compatible with the single host-star convention and which captures as much of the dynamical information about the planet as possible. We propose a simple and generic naming convention for all exoplanets which follows the provisional I.A.U. standard but more clearly indicates their dynamical status. The proposed convention is compatible with present usage and easily extendible to exoplanets around stars in systems of arbitrary multiplicity. We invite comments and discussion on the proposed convention, in the hope of a timely adoption by the I.A.U. Commissions 5, 8+24, 26, 42, 45 and 53.

astro-ph.SR↗

arXiv2010

The X-ray source content of the XMM-Newton Galactic Plane Survey

We report the results of an optical campaign carried out by the XMM-Newton Survey Science Centre with the specific goal of identifying the brightest X-ray sources in the XMM-Newton Galactic Plane Survey of Hands et al. (2004). In addition to photometric and spectroscopic observations obtained at the ESO-VLT and ESO-3.6m, we used cross-correlations with the 2XMMi, USNO-B1.0, 2MASS and GLIMPSE catalogues to progress the identification process. Active coronae account for 16 of the 30 identified X-ray sources. Many of the identified hard X-ray sources are associated with massive stars emitting at intermediate X-ray luminosities of 10^32-34 erg/s. Among these are a very absorbed likely hyper-luminous star with X-ray/optical spectra and luminosities comparable with those of eta Carina, a new X-ray selected WN8 Wolf-Rayet star, a new Be/X-ray star belonging to the growing class of Gamma-Cas analogs and a possible supergiant X-ray binary of the kind discovered recently by INTEGRAL. One of the sources, XGPS-25 has a counterpart which exhibits HeII 4686 and Bowen CIII-NIII emission lines suggesting a quiescent or X-ray shielded Low Mass X-ray Binary, although its properties might also be consistent with a rare kind of cataclysmic variable (CV). We also report the discovery of three new CVs, one of which is a likely magnetic system. The soft (0.4-2.0 keV) band LogN-LogS curve is completely dominated by active stars in the flux range of 1x10^-13 to 1x10^-14 erg/cm2/s. In total, we are able to identify a large fraction of the hard (2-10 keV) X-ray sources in the flux range of 1x10^-12 to 1x10^-13 erg/cm2/s with Galactic objects at a rate consistent with that expected for the Galactic contribution only. (abridged)

astro-ph.HE↗

arXiv2010

eROSITA on SRG: a X-ray all-sky survey mission

eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is the core instrument on the Russian Spektrum-Roentgen-Gamma (SRG) mission which is scheduled for launch in late 2012. eROSITA is fully approved and funded by the German Space Agency DLR and the Max-Planck-Society. The design driving science is the detection of 50 - 100 thousands Clusters of Galaxies up to redshift z ~ 1.3 in order to study the large scale structure in the Universe and test cosmological models, especially Dark Energy. This will be accomplished by an all-sky survey lasting for four years plus a phase of pointed observations. eROSITA consists of seven Wolter-I telescope modules, each equipped with 54 Wolter-I shells having an outer diameter of 360 mm. This would provide and effective area at 1.5 keV of ~ 1500 cm2 and an on axis PSF HEW of 15" which would provide an effective angular resolution of 25"-30". In the focus of each mirror module, a fast frame-store pn-CCD will provide a field of view of 1 deg in diameter for an active FOV of ~ 0.83 deg^2. At the time of writing the instrument development is currently in phase C/D.

astro-ph.IM↗

arXiv2010

Multi-site Observations of Pulsation in the Accreting White Dwarf SDSS J161033.64-010223.3 (V386 Ser)

Nonradial pulsations in the primary white dwarfs of cataclysmic variables can now potentially allow us to explore the stellar interior of these accretors using stellar seismology. In this context, we conducted a multi-site campaign on the accreting pulsator SDSS J161033.64-010223.3 (V386 Ser) using seven observatories located around the world in May 2007 over a duration of 11 days. We report the best fit periodicities here, which were also previously observed in 2004, suggesting their underlying stability. Although we did not uncover a sufficient number of independent pulsation modes for a unique seismological fit, our campaign revealed that the dominant pulsation mode at 609s is an evenly spaced triplet. The even nature of the triplet is suggestive of rotational splitting, implying an enigmatic rotation period of about 4.8 days. There are two viable alternatives assuming the triplet is real: either the period of 4.8 days is representative of the rotation period of the entire star with implications for the angular momentum evolution of these systems, or it is perhaps an indication of differential rotation with a fast rotating exterior and slow rotation deeper in the star. Investigating the possibility that a changing period could mimic a triplet suggests that this scenario is improbable, but not impossible. Using time-series spectra acquired in May 2009, we determine the orbital period of SDSS J161033.64-010223.3 to be 83.8 +/- 2.9 min. Three of the observed photometric frequencies from our May 2007 campaign appear to be linear combinations of the 609s pulsation mode with the first harmonic of the orbital period at 41.5min. This is the first discovery of a linear combination between nonradial pulsation and orbital motion for a variable white dwarf.

astro-ph.SR↗

arXiv2010

ARCRAIDER II: Arc search in a sample of non-Abell clusters

We present a search for gravitational arcs in a sample of X-ray luminous, medium redshift clusters of galaxies. The sample of clusters is called ARCRAIDER, is based on the ROSAT Bright Survey (RBS) and fulfills the following criteria: (a) X-ray luminosity Lx>=0.5x10^45erg/s (0.5-2keV band), (b) redshift range 0.1<=z<=0.52, (c) classified as clusters in the RBS, (d) not a member of the Abell catalogue and, finally, (e) visible from the ESO sites La Silla/Paranal (declination δ<=20deg). In total we found more than 35 (giant) arc/arclet candidates, including a possible radial arc, one galaxy-galaxy lensing event and a possible quasar triple image in 14 of the 21 clusters of galaxies. Hence 66% of the sample members are possible lenses.

astro-ph.CO↗

arXiv2009

The XMM-Newton Wide Angle Survey (XWAS): the X-ray spectrum of type-1 AGN

We discuss the broad band X-ray properties of one of the largest samples of X-ray selected type-1 AGN to date (487 objects in total), drawn from the XMM-Newton Wide Angle Survey. The objects cover 2-10 keV luminosities from ~10^{42}-10^{45} erg s^{-1} and are detected up to redshift ~4. We constrain the overall properties of the broad band continuum, soft excess and X-ray absorption, along with their dependence on the X-ray luminosity and redshift and we discuss the implications for models of AGN emission. We constrained the mean spectral index of the broad band X-ray continuum to =1.96+-0.02 with intrinsic dispersion sigma=0.27_{-0.02}^{+0.01}. The continuum becomes harder at faint fluxes and at higher redshifts and luminosities. The dependence of Gamma with flux is likely due to undetected absorption rather than to spectral variation. We found a strong dependence of the detection efficiency of objects on the spectral shape which can have a strong impact on the measured mean continuum shapes of sources at different redshifts and luminosities. We detected excess absorption in ~3% of our objects, with column densities ~a few x10^{22} cm^{-2}. The apparent mismatch between the optical classification and X-ray properties of these objects is a challenge for the standard AGN unification model. We found that the fraction of objects with detected soft excess is ~36%. Using a thermal model, we constrained the soft excess mean temperature and intrinsic dispersion to ~100 eV and sigma~34 eV. The origin of the soft excess as thermal emission from the accretion disk or Compton scattered disk emission is ruled out on the basis of the temperatures detected and the lack of correlation of the measured temperature with the X-ray luminosity (abridged).

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arXiv2009

Multi-wavelength study of XMMU J2235.3-2557: the most massive galaxy cluster at z > 1

[Abridged] XMMU J2235.3-2557 is one of the most distant X-ray selected clusters, spectroscopically confirmed at z=1.39. We characterize the galaxy populations of passive members, the thermodynamical properties of the hot gas, its metal abundance and the total mass of the system using imaging data with HST/ACS (i775 and z850 bands) and VLT/ISAAC (J and K_s bands), extensive spectroscopic data obtained with VLT/FORS2, and deep Chandra observations. Out of a total sample of 34 spectroscopically confirmed cluster members, we selected 16 passive galaxies within the central 2' (or 1 Mpc) with ACS coverage, and inferred star formation histories for a sub-sample of galaxies inside and outside the core by modeling their spectro-photometric data with spectral synthesis models, finding a strong mean age radial gradient. Chandra data show a regular elongated morphology, closely resembling the distribution of core galaxies, with a significant cool core. We measure a global X-ray temperature of kT=8.6(-1.2,+1.3) keV (68% c.l.). By detecting the rest-frame 6.7 keV Iron K line, we measure a metallicty Z= 0.26(+0.20,-0.16) Zsun. In the likely hypothesis of hydrostatic equilibrium, we obtain a total mass of Mtot(<1 Mpc)=(5.9+-1.3)10^14 Msun. Overall, our analysis implies that XMM2235 is the hottest and most massive bona-fide cluster discovered to date at z>1, with a baryonic content, both its galaxy population and intra-cluster gas, in a significantly advanced evolutionary stage at 1/3 of the current age of the Universe.

astro-ph.CO↗

arXiv2009

Optical identification of XMM sources in the CFHTLS

We present optical spectroscopic identifications of X-ray sources in ~3 square degrees of the XMM-Large Scale Structure survey (XMM-LSS), also covered by the Canada France Hawaii Telescope Legacy Survey (CFHTLS), obtained with the AAOmega instrument at the Anglo Australian Telescope. In a flux limited sample of 829 point like sources in the optical band with g' <~22 mag and the 0.5-2 keV flux > 1x10^{-15}erg/cm^2/s, we observed 695 objects and obtained reliable spectroscopic identification for 489 sources, ~59% of the overall sample. We therefore increase the number of identifications in this field by a factor close to five. Galactic stellar sources represent about 15% of the total (74/489). About 55% (267/489) are broad-line Active Galactic Nuclei (AGNs) spanning redshifts between 0.15 and 3.87 with a median value of 1.68. The optical-to-X-ray spectral index of the broad-line AGNs is 1.47, typical of optically-selected Type I quasars and is found to correlate with the rest frame X-ray and optical monochromatic luminosities at 2 keV and 2500 angstroms respectively. Consistent with previous studies, we find alpha_ox not to be correlated with z. In addition, 32 and 116 X-ray sources are, respectively absorption and emission-line galaxies at z<0.76. From a line ratio diagnostic diagram it is found that in about 50% of these emission line galaxies, the emission lines are powered significantly by the AGN. Thirty of the XMM sources are detected at one or more radio frequencies. In addition, 24 sources have ambiguous identification: in 8 cases, two XMM sources have a single optical source within 6 arcsecs of each of them, whereas, 2 and 14 XMM sources have, respectively, 3 and 2 possible optical sources within 6 arcsecs of each of them.

astro-ph.CO↗

arXiv2009

VLT optical observations of the isolated neutron star RX J0420.0-5022

X-ray observations performed with ROSAT led to the discovery of 7 radio-silent isolated neutron stars (INSs) which are detected only through the relatively dim and purely thermal X-ray emission from the cooling star surface. A few of these INSs (a.k.a. X-ray Dim INSs, or XDINSs) have been also detected at optical wavelengths where they seem to feature thermal spectra. Optical studies of XDINSs thus play a crucial role in mapping the temperature distribution on the neutron star surface and in investigating the existence of an atmosphere around the neutron star. The aim of this work is to investigate the optical identification of the XDINS RX J0420.0-5022, tentatively proposed by Haberl et al. (2004) based on VLT observations. We re-analysed the original observations of Haberl et al. to assess the detection significance of the proposed counterpart and we performed deeper VLT observations aiming at a higher confidence detection. With a ~2 sigma detection significance and a re-computed flux of B=27.52+/-0.61, we can not rule out that the proposed counterpart was spurious and produced by the halo of a very bright nearby star. While we could not detect the proposed counterpart in our deeper VLT observations, we found evidence for a marginally significant (~3.9 sigma) detection of a similarly faint object (B= 27.5+/-0.3), ~ 0.5" north of it and coincident with the updated Chandra position of RX J0420.0-5022. Interestingly, the angular separation is consistent with the upper limit on the RX J0420.0-5022 proper motion (Motch et al. 2009), which suggests that we might have actually detected the Haberl et al. proposed counterpart. From the flux of the putative RX J0420.0-5022 counterpart we can rule out a > 7 optical excess with respect to the extrapolation of the XMM-Newton spectrum.

astro-ph.HE↗

arXiv2009

The isolated neutron star RBS1774 revisited. Revised XMM-Newton X-ray parameters and an optical counterpart from deep LBT-observations

We report optical B-band observations with the Large Binocular Telescope LBT of the isolated neutron star RBS1774. The stacked image with total exposure 2.5h reveals a candidate optical counterpart at mB = 26.96 +- 0.20 at position RA(2000) = 21:43:03.4, DEC(2000)} = +06:54:17:5, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ~40 (15 - 60 at 1sigma confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star's surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve.

astro-ph.GA↗

arXiv2009

Proper motions of thermally emitting isolated neutron stars measured with Chandra

The remarkable astrometric capabilities of Chandra offer the possibility to measure proper motions of X-ray sources with an unprecedented accuracy in this wavelength range. We recently completed a proper motion survey of three of the seven thermally emitting radio-quiet isolated neutron stars (INSs) discovered in the ROSAT all-sky survey. These INSs (RX J0420.0-5022, RX J0806.4-4123, and RX J1308.6+2127) either lack an optical counterpart or have one so faint that ground based or space born optical observations push the current possibilities of the instrumentation to the limit. Pairs of ACIS observations were acquired 3 to 5 years apart to measure the displacement of the sources on the X-ray sky using as reference the background of extragalactic or remote Galactic X-ray sources. We derive 2 sigma upper limits of 123 mas/yr and 86 mas/yr on the proper motion of RX J0420.0-5022 and RX J0806.4-4123, respectively. RX J1308.6+2127 exhibits a very significant displacement (~ 9 sigma) yielding mu = 220 +/- 25 mas/yr, the second fastest measured among all ROSAT discovered INSs. The source is probably moving away rapidly from the Galactic plane at a speed which precludes any significant accretion of matter from the interstellar medium. Its transverse velocity of ~ 740 (d/700pc) km/s might be the largest of all ROSAT INSs and its corresponding spatial velocity stands among the fastest recorded for neutron stars. RX J1308.6+2127 is thus a middle-aged (age ~ 1 My) high velocity cooling neutron star. We investigate its possible origin in nearby OB associations or from a field OB star. In most cases, the flight time from birth place appears significantly shorter than the characteristic age derived from spin down rate. The distribution in transverse velocity of ROSAT INSs is not statistically different from that of normal radio pulsars.

astro-ph.HE↗

arXiv2008

The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue

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 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~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 .

astro-ph↗

arXiv2008

Average Fe K-alpha emission from distant AGN

One of the most important parameters in the XRB (X-ray background) synthesis models is the average efficiency of accretion onto SMBH (super-massive black holes). This can be inferred from the shape of broad relativistic Fe lines seen in X-ray spectra of AGN (active galactic nuclei). Several studies have tried to measure the mean Fe emission properties of AGN at different depths with very different results. We compute the mean Fe emission from a large and representative sample of AGN X-ray spectra up to redshift ~ 3.5. We developed a method of computing the rest-frame X-ray average spectrum and applied it to a large sample (more than 600 objects) of type 1 AGN from two complementary medium sensitivity surveys based on XMM-Newton data, the AXIS and XWAS samples. This method makes use of medium-to-low quality spectra without needing to fit complex models to the individual spectra but with computing a mean spectrum for the whole sample. Extensive quality tests were performed by comparing real to simulated data, and a significance for the detection of any feature over an underlying continuum was derived. We detect with a 99.9% significance an unresolved Fe K-alpha emission line around 6.4 keV with an EW ~ 90 eV, but we find no compelling evidence of any significant broad relativistic emission line in the final average spectrum. Deviations from a power law around the narrow line are best represented by a reflection component arising from cold or low-ionization material. We estimate an upper limit for the EW of any relativistic line of 400 eV at a 3 sigma confidence level. We also marginally detect the so-called Iwasawa-Taniguchi effect on the EW for the unresolved emission line, which appears weaker for higher luminosity AGN.

astro-ph↗

arXiv2008

2XMM J083026+524133: The most X-ray luminous cluster at redshift 1

In the distant universe X-ray luminous clusters of galaxies are rare objects. Large area surveys are therefore needed to probe the high luminosity end of the cluster population at redshifts z >= 1. We correlated extended X-ray sources from the second XMM-Newton source catalogue (2XMM) with the SDSS in order to identify new clusters of galaxies. Distant cluster candidates in empty SDSS fields were imaged in the R and z bands with the Large Binocular Telescope. We extracted the X-ray spectra of the cluster candidates and fitted thermal plasma models to the data. We determined the redshift 0.99 +-0.03 for 2XMM J083026+524133 from its X-ray spectrum. With a bolometric luminosity of 1.8 x 10^45 erg/sec this is the most X-ray luminous cluster at redshifts z >= 1. We measured a gas temperature of 8.2 +- 0.9 keV and and estimate a cluster mass M(500) = 5.6 x 10^14 M(solar). The optical imaging revealed a rich cluster of galaxies.

astro-ph↗

arXiv2008

Diffuse radio emission from clusters in the MareNostrum Universe simulation

Large-scale diffuse radio emission is observed in some clusters of galaxies. There is ample of evidence that the emission has its origin in synchrotron losses of relativistic electrons, accelerated in the course of clusters mergers. In a cosmological simulation we locate the structure formation shocks and estimate their radio emission. We proceed as follows: Introducing a novel approach to identify strong shock fronts in an SPH simulation, we determine the Mach number as well as the downstream density and temperature in the MareNostrum Universe simulation which has 2x1024^3 particles in a 500 Mpc/h box and was carried out with non-radiative physics. Then, we estimate the radio emission using the formalism derived in Hoeft & Brueggen (2007) and produce artificial radio maps of massive clusters. Several of our clusters show radio objects with similar morphology to large-scale radio relics found in the sky, whereas about half of the clusters show only very little radio emission. In agreement with observational findings, the maximum diffuse radio emission of our clusters depends strongly on their X-ray temperature. We find that the so-called accretion shocks cause only very little radio emission. We conclude that a moderate efficiency of shock acceleration, namely xi_e <= 0.005, and moderate magnetic fields in the region of the relics, namely 0.07 to 0.8 muGauss are sufficient to reproduce the number density and luminosity of radio relics.

astro-ph↗

arXiv2008

The serendipituous discovery of a short-period eclipsing polar in 2XMMp

We report the serendipituous discovery of the new eclipsing polar 2XMMp J131223.4+173659. Its striking X-ray light curve attracted immediate interest when we were visually inspecting the source products of the 2XMMp catalogue. This light curve revealed its likely nature as a magnetic cataclysmic variable of AM Herculis (or polar) type with an orbital period of ~92 min, which was confirmed by follow-up optical spectroscopy and photometry. 2XMMp J131223.4+173659 probably has a one-pole accretion geometry. It joins the group of now nine objects that show no evidence of a soft component in their X-ray spectra despite being in a high accretion state, thus escaping ROSAT/EUVE detection. We discuss the likely accretion scenario, the system parameters, and the spectral energy distribution.

astro-ph↗

arXiv2008

Indications for 3 Mpc-scale large-scale structure associated with an X-ray luminous cluster of galaxies at z=0.95

X-ray luminous clusters of galaxies at z~1 are emerging as major cosmological probes and are fundamental tools to study the cosmic large-scale structure and environmental effects of galaxy evolution at large look-back times. We present details of the newly-discovered galaxy cluster XMMU J0104.4-0630 at z=0.947 and a probable associated system in the LSS environment. The clusters were found in a systematic study for high-redshift systems using deep archival XMM-Newton data for the serendipitous detection and the X-ray analysis, complemented by optical/NIR imaging observations and spectroscopy of the main cluster. We find a well-evolved, intermediate luminosity cluster with Lx=(6.4+-1.3)x10^43 erg/s (0.5-2.0 keV) and strong central 1.4 GHz radio emission. The cluster galaxy population exhibits a pronounced transition toward bluer colors at cluster-centric distances of 1-2 core radii, consistent with an age difference of 1-2 Gyr for a single burst solar metallicity model. The second, less evolved X-ray cluster at a projected distance of 6.4 arcmin (~3 Mpc) and a concordant red-sequence color likely forms a cluster-cluster bridge with the main target as part of its surrounding large-scale structure at z~0.95.

astro-ph↗