MPI Fur Extraterrestrische Physik

Garching bei München, Germany

MPI Fur Extraterrestrische Physik

Garching bei München, Germany
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Beuermann K.,University of Gottingen | Burwitz V.,MPI fur extraterrestrische Physik | Reinsch K.,University of Gottingen | Schwope A.,Leibniz Institute for Astrophysics Potsdam | Thomas H.-C.,MPI fur Astrophysik
Astronomy and Astrophysics | Year: 2017

We report photometric and spectroscopic observations of the polar V358 Aqr (=RX J2316-0527) collected over 25 yr. It was discovered as a bright very soft X-ray source in the ROSAT All Sky Survey, but had lapsed into a low state when reobserved in 1993. We have obtained an optical photometric ephemeris, which is free of cycle count errors and allows to correctly phase events around the orbit even for observations that lie decades apart. V358 Aqr possesses an accreting pole in the upper hemisphere of the white dwarf that is visible over the entire orbital period of 209.45 min. The magnetic field strength derived from cyclotron line emission is 31.8 MG. The orbital motion of the cyclotron lines yields an inclination of 60° and an offset of the magnetic pole from the rotational axis of about 10°. The secondary star is of spectral type dM4.0 ± 0.5 and the distance is 540 ± 100 pc. V358 Aqr is peculiar in showing giant optical outbursts that bear all of the characteristics of stellar flares. With two flares observed in 72 h on source, the flare frequency may be high. The total energy radiated in the flare of 28 November 2010 exceeded 1036 erg. While the flares clearly occur on the secondary star, it seems that they may or may not be connected with coronal mass ejection and subsequent accretion onto the white dwarf. © ESO, 2017.

Churazov E.,MPI fur Astrophysik | Churazov E.,Space Research Institute | Khabibullin I.,MPI fur Astrophysik | Khabibullin I.,Space Research Institute | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2017

We use a model of the molecular gas distribution within ~100 pc from the centre of theMilky Way (Kruijssen, Dale & Longmore) to simulate time evolution and polarization properties of the reflected X-ray emission, associated with the past outbursts from Sgr A*.While this model is too simple to describe the complexity of the true gas distribution, it illustrates the importance and power of long-term observations of the reflected emission. We show that the variable part of X-ray emission observed by Chandra and XMM-Newton from prominent molecular clouds is well described by a pure reflectionmodel, providing strong support of the reflection scenario. While the identification of Sgr A* as a primary source for this reflected emission is already a very appealing hypothesis, a decisive test of this model can be provided by future X-ray polarimetric observations, which will allow placing constraints on the location of the primary source. In addition, X-ray polarimeters (like, e.g. XIPE) have sufficient sensitivity to constrain the line-of-sight positions of molecular complexes, removing major uncertainty in the model. © 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

Thomas H.-C.,MPI fur Astrophysik | Beuermann K.,Leibniz Institute for Astrophysics Potsdam | Reinsch K.,Leibniz Institute for Astrophysics Potsdam | Schwope A.D.,MPI fur Extraterrestrische Physik | Burwitz V.,MPI fur Astrophysik
Astronomy and Astrophysics | Year: 2012

We report optical and X-ray observations of the high-field polar RX J1007.5-2017 performed between 1990 and 2012. It has an orbital period of 208.60 min determined from the ellipsoidal modulation of the secondary star in an extended low state. The spectral flux of the dM3 - secondary star yields a distance of 790 ± 105 pc. At low accretion levels, RX J1007.5-2017 exhibits pronounced cyclotron emission lines. The second and third harmonic fall in the optical regime and yield a field strength in the accretion spot of 94 MG. The source is highly variable on a year-to-year basis and was encountered at visual magnitudes between V ∼ 20 and V ∼ 16. In the intermediate state of 1992 and 2000, the soft X-ray luminosity exceeds the sum of the luminosities of the cyclotron source, the hard X-ray source, and the accretion stream by an order of magnitude. An X-ray high state, corresponding to the brightest optical level, has apparently not been observed so far. © ESO, 2012.

Das P.,MPI fur Extraterrestrische Physik | Gerhard O.,MPI fur Extraterrestrische Physik | Churazov E.,MPI fur Astrophysik | Churazov E.,Space Research Institute IKI | Zhuravleva I.,MPI fur Astrophysik
Monthly Notices of the Royal Astronomical Society | Year: 2010

We use a new non-parametric Bayesian approach to obtain the most probable mass distributions and circular velocity curves along with their confidence ranges, given deprojected density and temperature profiles of the hot gas surrounding X-ray bright elliptical galaxies. For a sample of six X-ray bright ellipticals, we find that all circular velocity curves are rising in the outer parts due to a combination of a rising temperature profile and a logarithmic pressure gradient that increases in magnitude. Therefore at large radii, mass density profiles rise more steeply than isothermal profiles, implying that we are probing the more massive group-sized haloes in which these galaxies are embedded. Comparing the circular velocity curves we obtain from X-rays to those obtained from dynamical models, we find that the former are often lower in the central -10 kpc. This is probably due to a combination of (i) non-thermal contributions of up to -35 per cent in the pressure (with stronger effects in NGC-4486), (ii) multiple-temperature components in the hot gas, (iii) incomplete kinematic spatial coverage in the dynamical models and (iv) mass profiles that are insufficiently general in the dynamical modelling. Complementing the total mass information from the X-rays with photometry and stellar population models to infer the dark matter content, we find evidence for massive dark matter haloes with dark matter mass fractions of -35-80 per cent at-2Re, rising to a maximum of 80-90 per cent at the outermost radii. We also find that the six galaxies follow a Tully-Fisher relation with a slope of -4 and that their circular velocities at-1Re-correlate strongly with the velocity dispersion of the local environment. As a result, the galaxy luminosity at-1Re-also correlates with the velocity dispersion of the environment. These relations suggest a close link between the properties of central X-ray bright elliptical galaxies and their environments. © 2010 The Authors. Journal compilation © 2010 RAS.

Churazov E.,Max Planck Institute for Astrophysics | Churazov E.,Space Research Institute IKI | Tremaine S.,Institute for Advanced Study | Forman W.,Harvard - Smithsonian Center for Astrophysics | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

We analyse six X-ray bright elliptical galaxies, observed with Chandra and XMM-Newton, and approximate their gravitational potentials by isothermal spheres φ =v2c log r over a range of radii from ∼0.5 to ∼25 kpc. We then compare the circular speed vc derived from X-ray data with the estimators available from optical data. In particular, we discuss two simple and robust procedures for evaluating the circular speed of the galaxy using the observed optical surface brightness and the line-of-sight velocity dispersion profiles. The best-fitting relation between the circular speeds derived from optical observations of stars and X-ray observations of hot gas is vc,opt ≃ η vc,X, where η = 1.10-1.15 (depending on the method), suggesting, albeit with large statistical and systematic uncertainties, that non-thermal pressure on average contributes ∼20-30 per cent of the gas thermal pressure. © 2010 The Authors. Journal compilation © 2010 RAS.

Churazov E.,Max Planck Institute for Astrophysics | Churazov E.,Space Research Institute IKI | Vikhlinin A.,Harvard - Smithsonian Center for Astrophysics | Zhuravleva I.,Max Planck Institute for Astrophysics | And 7 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

X-ray surface brightness fluctuations in the core (650 × 650 kpc) region of the Coma cluster observed with XMM-Newton and Chandra are analysed using a 2D power spectrum approach. The resulting 2D spectra are converted to 3D power spectra of gas density fluctuations. Our independent analyses of the XMM-Newton and Chandra observations are in excellent agreement and provide the most sensitive measurements of surface brightness and density fluctuations for a hot cluster. We find that the characteristic amplitude of the volume filling density fluctuations relative to the smooth underlying density distribution varies from 7-10 per cent on scales of ~500kpc down to ~5 per cent on scales of ~30kpc. On smaller spatial scales, projection effects smear the density fluctuations by a large factor, precluding strong limits on the fluctuations in 3D. On the largest scales probed (hundreds of kpc), the dominant contributions to the observed fluctuations most likely arise from perturbations of the gravitational potential by the two most massive galaxies in Coma, NGC4874 and NGC4889, and the low-entropy gas brought to the cluster by an infalling group. Other plausible sources of X-ray surface brightness fluctuations are discussed, including turbulence, metal abundance variations and unresolved sources. Despite a variety of possible origins for density fluctuations, the gas in the Coma cluster core is remarkably homogeneous on scales from ~500 to ~30kpc. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.

Braig C.,Friedrich - Schiller University of Jena | Predehl P.,MPI fur Extraterrestrische Physik
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

Arrays of achromatic Fresnel lenses are investigated for future high-resolution X-ray imaging missions. Unlike single-focus instruments, parallel arrangements of numerous tiny telescopes provide an easy and natural approach to spectroscopic observations in several energy bands, at an unprecedented short focal length of few 10 3m. We suggest an optimized design with an angular resolution around 1 mas between 5 and 10 keV and analyze its optical capabilities as well as issues like the background problem which affects the achievable signal-to-noise ratio. An astronomical simulation is performed on the sun-like star Capella. © 2010 SPIE.

Das P.,MPI fur Extraterrestrische Physik | Gerhard O.,MPI fur Extraterrestrische Physik | Mendez R.H.,University of Hawaii at Manoa | Teodorescu A.M.,University of Hawaii at Manoa | de Lorenzi F.,MPI fur Extraterrestrische Physik
Monthly Notices of the Royal Astronomical Society | Year: 2011

We create dynamical models of the massive elliptical galaxy, NGC 4649, using the N-body made-to-measure code, nmagic, and kinematic constraints from long-slit and planetary nebula (PN) data. We explore a range of potentials based on previous determinations from X-ray observations and a dynamical model fitting globular cluster (GC) velocities and a stellar density profile. The X-ray mass distributions are similar in the central region but have varying outer slopes, while the GC mass profile is higher in the central region and on the upper end of the range further out. Our models cannot differentiate between the potentials in the central region, and therefore if non-thermal pressures or multi-phase components are present in the hot gas, they must be smaller than previously inferred. In the halo, we find that the PN velocities are sensitive tracers of the mass, preferring a less massive halo than that derived from the GC mass profile, but similar to one of the mass distributions derived from X-rays. Our results show that the GCs may form a dynamically distinct system, and that the properties of the hot gas derived from X-rays in the outer halo have considerable uncertainties that need to be better understood. Estimating the mass in stars using photometric information and a stellar population mass-to-light ratio, we infer a dark matter mass fraction in NGC 4649 of ~0.39 at 1R e (10.5kpc) and ~0.78 at 4R e. We find that the stellar orbits are isotropic to mildly radial in the central ~6kpc depending on the potential assumed. Further out, the orbital structure becomes slightly more radial along R and more isotropic along z, regardless of the potential assumed. In the equatorial plane, azimuthal velocity dispersions dominate over meridional velocity dispersions, implying that meridional velocity anisotropy is the mechanism for flattening the stellar system. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Greiner J.,MPI fur extraterrestrische Physik | Mannheim K.,University of Würzburg
Experimental Astronomy | Year: 2012

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the corresponding telescopes placed on a separate satellite. The Gamma-Ray Imaging, Polarimetry and Spectroscopy ("GRIPS") mission with its three instruments Gamma-Ray Monitor (GRM), X-Ray Monitor (XRM) and InfraRed Telescope (IRT) addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate γ-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts. © 2011 Springer Science+Business Media B.V.

Longobardi A.,MPI fur extraterrestrische Physik | Arnaboldi M.,European Southern Observatory | Gerhard O.,MPI fur extraterrestrische Physik
Astrophysics and Space Science Proceedings | Year: 2016

Cosmological simulations allow us to make detailed predictions for the evolution of galaxy halos and intracluster light (ICL) in cluster environments, but the extremely low surface brightnesses of such contents make it difficult to gather observational constraints. Planetary nebulas (PNs) offer a unique tool to investigate these environments owing to their strong [OIII] emission line. Making use of a deep and extended PN sample we show that the halo of M87 and the Virgo ICL are dynamically distinct components with different parent stellar populations. © Springer International Publishing Switzerland 2016.

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