arXiv subjects

Axel D. Schwope

Publications and source records attributed to Axel D. Schwope.

At least 37 records · Page 2Linked to original sources

arXiv2014

Kinematic analysis of a sample of X-ray luminous distant galaxy clusters. The $L_X$ - $σ_v$ relation in the $z>0.6$ universe

Observations and cosmological simulations show galaxy clusters as a family of nearly self-similar objects with properties that can be described by scaling relations as a function of e.g. mass and time. Here we study the scaling relations between the galaxy velocity dispersion and X-ray quantities like X-ray bolometric luminosity and temperature in galaxy clusters at high redshifts (0.64 $\leq$ z $\leq$ 1.46). We also compare our results with the similar study of the local HIFLUGCS sample. For the analysis, we use a set of 15 distant galaxy clusters extracted from the literature plus a sample of 10 newly discovered clusters selected in X-rays by the \XMM Distant Cluster Project (XDCP) with more than 10 confirmed spectroscopic members per cluster. We also study the evolution of this scaling relation by comparing the high redshift results with the data from the local HIFLUGCS sample. We also investigated the $L_X - T_X$ and the $σ_v - T_X$ relations for the 15 clusters in the literature sample. We report the results of the X-ray and kinematic analysis of 10 newly detected high redshift clusters and provide their spectroscopic and kinematic details. For the entire, distant sample we find a slope fully consistent with the one typical of local clusters, albeit with a large associated uncertainty. The study on the evolution of the amplitude reveals a positive offset if the self-similar evolution is neglected, hence possibly indicating the need for including evolutionary effects. However, the $L_X - T_X$ relation is found to be in good agreement with the local relation without any significant redshift evolution. Finally, the $σ_v - T_X$ relation appears to slightly deviate from the theoretical expectation that galaxies and gas particles have a similar specific kinetic energy. However, the associated uncertainty is currently too large for making any conclusive statement in this regard.

astro-ph.CO↗

arXiv2013

The space density of magnetic cataclysmic variables

We use the complete, X-ray flux-limited ROSAT Bright Survey (RBS) to measure the space density of magnetic cataclysmic variables (mCVs). The survey provides complete optical identification of all sources with count rate >0.2/s over half the sky ($|b|>30^\circ$), and detected 6 intermediate polars (IPs) and 24 polars. If we assume that the 30 mCVs included in the RBS are representative of the intrinsic population, the space density of mCVs is $8^{+4}_{-2} \times 10^{-7}\,{\rmpc^{-3}}$. Considering polars and IPs separately, we find $ρ_{polar}=5^{+3}_{-2} \times 10^{-7}\,{\rm pc^{-3}}$ and $ρ_{IP}=3^{+2}_{-1} \times 10^{-7}\,{\rm pc^{-3}}$. Allowing for a 50% high-state duty cycle for polars (and assuming that these systems are below the RBS detection limit during their low states) doubles our estimate of $ρ_{polar}$ and brings the total space density of mCVs to $1.3^{+0.6}_{-0.4} \times 10^{-6}\,{\rm pc^{-3}}$. We also place upper limits on the sizes of faint (but persistent) mCV populations that might have escaped detection in the RBS. Although the large uncertainties in the $ρ$ estimates prevent us from drawing strong conclusions, we discuss the implications of our results for the evolutionary relationship between IPs and polars, the fraction of CVs with strongly magnetic white dwarfs (WDs), and for the contribution of mCVs to Galactic populations of hard X-ray sources at $L_X \ga 10^{31} {\rm erg/s}$. Our space density estimates are consistent with the very simple model where long-period IPs evolve into polars and account for the whole short-period polar population. We find that the fraction of WDs that are strongly magnetic is not significantly higher for CV primaries than for isolated WDs. Finally, the space density of IPs is sufficiently high to explain the bright, hard X-ray source population in the Galactic Centre.

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arXiv2012

On the HU Aquarii planetary system hypothesis

In this work, we investigate the eclipse timing of the polar binary HU Aquarii that has been observed for almost two decades. Recently, Qian et al. attributed large (O-C) deviations between the eclipse ephemeris and observations to a compact system of two massive jovian companions. We improve the Keplerian, kinematic model of the Light Travel Time (LTT) effect and re-analyse the whole currently available data set. We add almost 60 new, yet unpublished, mostly precision light curves obtained using the time high-resolution photo-polarimeter OPTIMA, as well as photometric observations performed at the MONET/N, PIRATE and TCS telescopes. We determine new mid--egress times with a mean uncertainty at the level of 1 second or better. We claim that because the observations that currently exist in the literature are non-homogeneous with respect to spectral windows (ultraviolet, X-ray, visual, polarimetric mode) and the reported mid--egress measurements errors, they may introduce systematics that affect orbital fits. Indeed, we find that the published data, when taken literally, cannot be explained by any unique solution. Many qualitatively different and best-fit 2-planet configurations, including self-consistent, Newtonian N-body solutions may be able to explain the data. However, using high resolution, precision OPTIMA light curves, we find that the (O-C) deviations are best explained by the presence of a single circumbinary companion orbiting at a distance of ~4.5 AU with a small eccentricity and having ~7 Jupiter-masses. This object could be the next circumbinary planet detected from the ground, similar to the announced companions around close binaries HW Vir, NN Ser, UZ For, DP Leo or SZ Her, and planets of this type around Kepler-16, Kepler-34 and Kepler-35.

astro-ph.EP↗

arXiv2011

Cataclysmic Variables from SDSS. VIII. The Final Year (2007-2008)

This paper completes the series of cataclysmic variables (CVs) identified from the Sloan Digital Sky Survey I/II. The coordinates, magnitudes and spectra of 33 CVs are presented. Among the 33 are eight systems known previous to SDSS (CT Ser, DO Leo, HK Leo, IR Com, V849 Her, V405 Peg, PG1230+226 and HS0943+1404), as well as nine objects recently found through various photometric surveys. Among the systems identified since the SDSS are two polar candidates, two intermediate polar candidates and one candidate for containing a pulsating white dwarf. Our followup data have confirmed a polar candidate from Paper VII and determined tentative periods for three of the newly identified CVs. A complete summary table of the 285 CVs with spectra from SDSS I/II is presented as well as a link to an online table of all known CVs from both photometry and spectroscopy that will continue to be updated as future data appear.

astro-ph.SR↗

arXiv2011

Discovery of the X-ray selected galaxy cluster XMMU J0338.8+0021 at z = 1.49 - Indications for a young system with a forming brightest galaxy

We report on the discovery of a galaxy cluster at z = 1.490 originally selected as an extended X-ray source in the XMM-Newton Distant Cluster Project. Further observations carried out with the VLT-FORS2 spectrograph allowed the spectroscopic confirmation of seven secure cluster members, providing a median system redshift of z = 1.490 +/- 0.009. The color magnitude diagram of XMMU J0338.8+0021 reveals the presence of a well populated red sequence with z-H ~ 3, albeit with an apparent significant scatter in color. Since we do not detect indications for strong star formation activity in any of the objects, the color spread could indicate different stellar ages of the member galaxies. In addition, we found the brightest cluster galaxy in a very active dynamical state, with an interacting, merging companion located at a physical projected distance of d ~ 20kpc. From the X-ray luminosity we estimate a cluster mass of M200 ~ 1.2 x 10^(14) Msun. The data seem to suggest a scenario in which XMMU J0338.8+0021 is a young system, possibly caught in a moment of active ongoing mass assembly.

astro-ph.CO↗

arXiv2011

Discovery of a massive X-ray luminous galaxy cluster at z=1.579

We report on the discovery of a very distant galaxy cluster serendipitously detected in the archive of the XMM-Newton mission, within the scope of the XMM-Newton Distant Cluster Project (XDCP). XMMUJ0044.0-2033 was detected at a high significance level (5sigma) as a compact, but significantly extended source in the X-ray data, with a soft-band flux f(r<40")=(1.5+-0.3)x10^(-14) erg/s/cm2. Optical/NIR follow-up observations confirmed the presence of an overdensity of red galaxies matching the X-ray emission. The cluster was spectroscopically confirmed to be at z=1.579 using ground-based VLT/FORS2 spectroscopy. The analysis of the I-H colour-magnitude diagram shows a sequence of red galaxies with a colour range [3.7 < I-H < 4.6] within 1' from the cluster X-ray emission peak. However, the three spectroscopic members (all with complex morphology) have significantly bluer colours relative to the observed red-sequence. In addition, two of the three cluster members have [OII] emission, indicative of on-going star formation. Using the spectroscopic redshift we estimated the X-ray bolometric luminosity, Lbol = 5.8x10^44 erg/s, implying a massive galaxy cluster. This places XMMU J0044.0-2033 at the forefront of massive distant clusters, closing the gap between lower redshift systems and recently discovered proto- and low-mass clusters at z >1.6.

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arXiv2011

The SDSS White Dwarf - M Star Library

The Sloan Digital Sky Survey (SDSS), originally targeted at quasi-stellar objects, has provided us with a wealth of astronomical byproducts through the last decade. Since then, the number of white dwarfs (WDs) with physically bound main-sequence star companions (mostly dM stars) has increased radically, allowing for fundamentally new insights into stellar physics. Different methods for the retrieval and follow-up analysis of SDSS WD-dM binaries have been applied in the literature, leading to a rising number of WD-dM catalogs. Here we present a detailed literature search, coupled with our own hunting for SDSS WD-dMs by color selection, the outcome being named the "SDSS White Dwarf - M Star Library". We also explain improvements of our automated spectral analysis method.

astro-ph.SR↗

arXiv2011

The X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.56 - The dawn of starburst activity in cluster cores

Observational galaxy cluster studies at z>1.5 probe the formation of the first massive M>10^14 Msun dark matter halos, the early thermal history of the hot ICM, and the emergence of the red-sequence population of quenched early-type galaxies. We present first results for the newly discovered X-ray luminous galaxy cluster XMMU J1007.4+1237 at z=1.555, detected and confirmed by the XMM-Newton Distant Cluster Project (XDCP) survey. We selected the system as a serendipitous weak extended X-ray source in XMM-Newton archival data and followed it up with two-band near-infrared imaging and deep optical spectroscopy. We can establish XMMU J1007.4+1237 as a spectroscopically confirmed, massive, bona fide galaxy cluster with a bolometric X-ray luminosity of Lx=(2.1+-0.4)\times 10^44 erg/s, a red galaxy population centered on the X-ray emission, and a central radio-loud brightest cluster galaxy. However, we see evidence for the first time that the massive end of the galaxy population and the cluster red-sequence are not yet fully in place. In particular, we find ongoing starburst activity for the third ranked galaxy close to the center and another slightly fainter object. At a lookback time of 9.4Gyr, the cluster galaxy population appears to be caught in an important evolutionary phase, prior to full star-formation quenching and mass assembly in the core region. X-ray selection techniques are an efficient means of identifying and probing the most distant clusters without any prior assumptions about their galaxy content.

astro-ph.CO↗

arXiv2010

A pan-chromatic view of the galaxy cluster XMMU J1230.3+1339 at z=0.975 - Observing the assembly of a massive system

We present a comprehensive galaxy cluster study of XMMU J1230.3+1339 based on a joint analysis of X-ray data, optical imaging and spectroscopy observations, weak lensing results, and radio properties for achieving a detailed multi-component view of this newly discovered system at z=0.975. We find an optically very rich and massive system with M200$\simeq$(4.2$\pm$0.8)$\times$10^14 M$\sun$, Tx$\simeq$5.3(+0.7--0.6)keV, and Lx$\simeq$(6.5$\pm$0.7)$\times$10^44 erg/s, for which various widely used mass proxies are measured and compared. We have identified multiple cluster-related components including a central fly-through group close to core passage with associated marginally extended 1.4GHz radio emission possibly originating from the turbulent wake region of the merging event. On the cluster outskirts we see evidence for an on-axis infalling group with a second Brightest Cluster Galaxy (BCG) and indications for an additional off-axis group accretion event. We trace two galaxy filaments beyond the nominal cluster radius and provide a tentative reconstruction of the 3D-accretion geometry of the system. In terms of total mass, ICM structure, optical richness, and the presence of two dominant BCG-type galaxies, the newly confirmed cluster XMMU J1230.3+1339 is likely the progenitor of a system very similar to the local Coma cluster, differing by 7.6 Gyr of structure evolution.

astro-ph.CO↗

arXiv2009

Cataclysmic Variables from SDSS VII. The Seventh Year (2006)

Coordinates, magnitudes and spectra are presented for 39 cataclysmic variables found in Sloan Digital Sky Survey spectra that were primarily obtained in 2006. Of these, 12 were CVs identified prior to the SDSS spectra (GY Cnc, GO Com, ST LMi, NY Ser, MR Ser, QW Ser, EU UMa, IY UMa, HS1340+1524, RXJ1610.1+0352, Boo 1, Leo 5). Follow-up spectroscopic observations of seven systems (including one from year 2005 and another from year 2004) were obtained, resulting in estimates of the orbital periods for 3 objects. The new CVs include two candidates for high inclination, eclipsing systems, 4 new Polars and three systems whose spectra clearly reveal atmospheric absorption lines from the underlying white dwarf.

astro-ph.GA↗

arXiv2008

The Subaru/XMM-Newton Deep Survey (SXDS): III. X-Ray Data

We present the X-ray source catalog in the Subaru/XMM-Newton deep survey. A continuous area of 1.14 deg^2 centered at R.A. = 02h18m and Dec. = -05d is mapped by seven pointings with XMM-Newton covering the 0.2-10 keV band. From the combined images of the EPIC pn and MOS cameras, we detect 866, 1114, 645, and 136 sources with sensitivity limits of 6x10^{-16}, 8x10^{-16}, 3x10^{-15}, and 5x10^{-15} erg cm^{-2} s^{-1} in the 0.5-2, 0.5-4.5, 2-10, and 4.5-10 keV bands, respectively, with detection likelihood >= 7 (corresponding to a confidence level of 99.91%). The catalog consists of 1245 sources in total including 32 extended-source candidates. The averaged log N-log S relations are in good agreement with previous results, bridging the flux range between Chandra deep surveys and brighter surveys. The log N-log S relations show significant spatial variation among pointings on a scale of 0.2 deg^2. Analyzing the auto correlation function, we detect significant clustering signals from the 0.5-2 keV band sample, which can be fit with a power law form (θ/θ_c)^{-0.8} with a correlation length of θ_c=5.9^{+1.0}_{-0.9} arcsec when the integral constraint term is included. In the 2-10 keV band, however, the clustering is not significant with a 90% upper limit of θ_c < 1.5 arcsec.

astro-ph↗

arXiv2006

Spitzer IRS Spectroscopy of Intermediate Polars: Constraints on Mid-Infrared Cyclotron Emission

We present Spitzer Infrared Spectrograph (IRS) observations of eleven intermediate polars (IPs). Spectra covering the wavelength range from 5.2 to 14 $μ$m are presented for all eleven objects, and longer wavelength spectra are presented for three objects (AE Aqr, EX Hya, and V1223 Sgr). We also present new, moderate resolution (R $\sim$ 2000) near-infrared spectra for five of the program objects. We find that, in general, the mid-infrared spectra are consistent with simple power laws that extend from the optical into the mid-infrared. There is no evidence for discrete cyclotron emission features in the near- or mid-infrared spectra for any of the IPs investigated. If cyclotron emission is occurring in the 5.2 to 14.0 $μ$m bandpass it constitutes less than 1% of the bolometric luminosity of any of the IPs. We discuss our results in the context of the standard model for IPs.

astro-ph↗

arXiv2006

The complex X-ray spectrum of the isolated neutron star RBS1223

We present a first analysis of a deep X-ray spectrum of the isolated neutron star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring observations in 2005/2006 were combined with archival observations obtained in 2003 and 2004 to form a spin-phase averaged spectrum containing 290000 EPIC-pn photons. This spectrum shows higher complexity than its predecessors, and can be parameterised with two Gaussian absorption lines superimposed on a blackbody. The line centers, E_2 ~ 2E_1, could be regarded as supporting the cyclotron interpretation of the absorption features in a field B ~ 4 x 10**13 G. The flux ratio of those lines does not support this interpretation. Hence, either feature might be of truly atomic origin.

astro-ph↗

arXiv2000

Accretion Stream Mapping of HU Aquarii

We present a new mapping algorithm, the "Accretion Stream Mapping (ASM)" which uses the full phase-coverage of a light curve to derive spatially resolved intensity distributions along the accretion stream in magnetic cataclysmic variables of AM Herculis type (polars). The surface of the accretion stream is approximated as a duodecadon shaped tube. After successfully testing this method on artificial data we applied it to emission line light curves of Hbeta, Hgamma and He II lambda 4686 of the bright eclipsing polar HU Aqr. We find Hydrogen and Helium line emission bright in the threading region of the stream where the stream couples onto magnetic field lines. It is particularly interesting, that the stream is bright on the irradiated side, facing the white dwarf, which highlights the interplay of collisional and radiative excitation/ionization.

astro-ph↗

arXiv1998

Modelling of the magnetic accretion flow in HU Aquarii

We present a magnetic stripping model for AM Her type objects. Our model is based on an equilibrium condition between ram pressure and magnetic pressure in a stiff dipolar magnetic field. We investigate the detailed geometry of the stripping process, most of which can be tackled analytically. By involving additional numerical calculations, the model allows the prediction of phase-resolved spectra and Doppler tomograms. The emission line features from the companion star, the horizontal stream and the accretion curtain are identified with the emission line components found by Gaussian fitting to observational data of HU Aqr in its high accretion state. Given the simplicity of the model, its agreement with the observation is remarkably good and enables and radii, total mass accretion rate, bulk temperature, and coupling density.

astro-ph↗

arXiv1998

Tomography of Polars

We are reviewing the power of Doppler tomography for detailed investigations of polars (magnetic cataclysmic binaries without accretion disk). Using high-resolution spectroscopy in combination with tomography as analytic tool, the structure and extent of the accretion flows and accretion curtains in the binaries can be uncovered and the irradiated and non-irradiated parts of the mass-donating secondary stars can be made visible. In addition we show, how basic system parameters like the binary inclination and the mass ratio can be addressed by tomography.

astro-ph↗

arXiv1998

Accretion Stream Mapping

We present a new mapping algorithm, the Accretion Stream Mapping, which uses the complete emission-line light curve to derive spatially resolved intensity distributions along the stream on a surface created as a duodecadon shaped tube. We successfully test this method on artificial data and then applied it to emission line light curves in Hbeta, Hgamma and HeII 4686 of the magnetic CV HU Aqr. We find Balmer emission near the threading point in the stream facing the white dwarf and Helium emission all over the magnetic part of the stream.

astro-ph↗

arXiv1997

Polars -- multisite emission -- multiwavelength observation

We review the main observational characteristics of AM Herculis stars (polars) at X-ray, EUV, UV, IR and optical wavelengths. Particular emphasis is given to multi-epoch, multi-wavelength observations of the eclipsing polar HU Aqr (RX J2107.9-0518). In AM Herculis stars the broad-band spectral energy distribution from X-rays to the IR is governed by only very small structures: the hot accretion regions on the footpoints af accreting field lines. The most extended structures in the binary systems on the other hand, the mass-donating secondary stars and the accretion streams, distinctly appear only as Doppler-shifted emission or absorption lines. They can best be studied by investigating selected narrow spectral features in the optical, ultraviolet or the near infrared. In this contribution both aspects will be highlighted, the structure of the accretion regions as inferred from multi-wavelength observations with low or no spectral resolution, as well as the structure of the secondary stars and the accretion streams as inferred from high-resolution spectral observations and Doppler mapping.

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