Time filter

Source Type

Garching bei München, Germany

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. Source

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. Source

Greiner J.,MPI Fur Extraterrestrische Physik | Mannheim K.,University of Wurzburg
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. Source

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. Source

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. Source

Discover hidden collaborations