Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics

Bamberg, Germany

Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics

Bamberg, Germany
SEARCH FILTERS
Time filter
Source Type

Keck M.L.,Boston University | Brenneman L.W.,Harvard - Smithsonian Center for Astrophysics | Ballantyne D.R.,Georgia Institute of Technology | Bauer F.,University of Santiago de Chile | And 21 more authors.
Astrophysical Journal | Year: 2015

We present X-ray timing and spectral analyses of simultaneous 150 ks Nuclear Spectroscopic Telescope Array (NuSTAR) and Suzaku X-ray observations of the Seyfert 1.5 galaxy NGC 4151. We disentangle the continuum emission, absorption, and reflection properties of the active galactic nucleus (AGN) by applying inner accretion disk reflection and absorption-dominated models. With a time-averaged spectral analysis, we find strong evidence for relativistic reflection from the inner accretion disk. We find that relativistic emission arises from a highly ionized inner accretion disk with a steep emissivity profile, which suggests an intense, compact illuminating source. We find a preliminary, near-maximal black hole spin a > 0.9 accounting for statistical and systematic modeling errors. We find a relatively moderate reflection fraction with respect to predictions for the lamp post geometry, in which the illuminating corona is modeled as a point source. Through a time-resolved spectral analysis, we find that modest coronal and inner disk reflection (IDR) flux variation drives the spectral variability during the observations. We discuss various physical scenarios for the IDR model and we find that a compact corona is consistent with the observed features. © 2015. The American Astronomical Society. All rights reserved.


Becker P.A.,George Mason University | Klochkov D.,University of Tübingen | Schonherr G.,Leibniz Institute for Astrophysics Potsdam | Nishimura O.,Nagano National College of Technology | And 6 more authors.
Astronomy and Astrophysics | Year: 2012

Context. Accretion-powered X-ray pulsars exhibit significant variability of the cyclotron resonance scattering feature (CRSF) centroid energy on pulse-to-pulse timescales, and also on much longer timescales. Two types of spectral variability are observed. For sources in group 1, the CRSF energy is negatively correlated with the variable source luminosity, and for sources in group 2, the opposite behavior is observed. The physical basis for this bimodal behavior is currently not well understood. Aims. We explore the hypothesis that the accretion dynamics in the group 1 sources is dominated by radiation pressure near the stellar surface, and that Coulomb interactions decelerate the gas to rest in the group 2 sources. Methods. We derive a new expression for the critical luminosity, L crit, such that radiation pressure decelerates the matter to rest in sources with X-ray luminosity L X > L crit. The formula for L crit is based on a simple physical model for the structure of the accretion column in luminous X-ray pulsars that takes into account radiative deceleration, the energy dependence of the cyclotron cross section, the thermodynamics of the accreting gas, the dipole structure of the pulsar magnetosphere, and the diffusive escape of radiation through the column walls. We show that for typical neutron star parameters, L crit = 1.5 × 10 37B 12 16/15 erg, s -1, where B 12 is the surface magnetic field strength in units of 10 12 G. Results. The formula for the critical luminosity is evaluated for five sources, using the maximum value of the CRSF centroid energy to estimate the surface magnetic field strength B 12. The results confirm that the group 1 sources are supercritical (L X > L crit) and the group 2 sources are subcritical (L X < L crit), although the situation is less clear for those highly variable sources that cross over the line L X = L crit. We also explain the variation of the CRSF energy with luminosity as a consequence of the variation of the characteristic emission height. The sign of this dependence is opposite in the supercritical and subcritical cases, hence creating the observed bimodal behavior. Conclusions. We have developed a new model for the critical luminosity in accretion-powered X-ray pulsars that explains the bimodal dependence of the CRSF centroid energy on the X-ray luminosity L X. Our model provides a physical basis for the observed variation of the CRSF energy as a function of L X for both the group 1 (supercritical) and the group 2 (subcritical) sources as a result of the variation of the emission height in the column. © 2012 ESO.


Vasudevan R.V.,Institute of Astronomy | Fabian A.C.,Institute of Astronomy | Reynolds C.S.,Institute of Astronomy | Reynolds C.S.,University of Maryland University College | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2016

The cosmic X-ray background (CXB) is the total emission from past accretion activity on to supermassive black holes in active galactic nuclei (AGN) and peaks in the hard X-ray band (30 keV). In this paper, we identify a significant selection effect operating on the CXB and flux-limited AGN surveys, and outline how they must depend heavily on the spin distribution of black holes. We show that, due to the higher radiative efficiency of rapidly spinning black holes, they will be over-represented in the X-ray background, and therefore could be a dominant contributor to the CXB. Using a simple bimodal spin distribution, we demonstrate that only 15 per cent maximally spinning AGN can produce 50 per cent of the CXB. We also illustrate that invoking a small population of maximally spinning black holes in CXB synthesis models can reproduce the CXB peak without requiring large numbers of Compton-thick AGN. The spin bias is even more pronounced for flux-limited surveys: 7 per cent of sources with maximally spinning black holes can produce half of the source counts. The detectability for maximum spin black holes can be further boosted in hard (>10 keV) X-rays by up to ~60 per cent due to pronounced ionized reflection, reducing the percentage of maximally spinning black holes required to produce half of the CXB or survey number counts further. A host of observations are consistent with an over-representation of high-spin black holes. Future NuSTAR and ASTRO-H hard X-ray surveys will provide the best constraints on the role of spin within the AGN population. © 2016 The Authors.


Fabian A.C.,Institute of Astronomy | Parker M.L.,Institute of Astronomy | Wilkins D.R.,Institute of Astronomy | Miller J.M.,University of Michigan | And 3 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

We discuss the application of simple relativistically blurred X-ray reflection models to the determination of the spin and the inner radius of the disc in accreting black holes. Observationally, the nature of the corona is uncertain a priori, but a robust determination of the inner disc radius can be made when the disc emissivity index is tightly constrained. When the inner disc is well illuminated, the black hole spin can also be determined. Using reflection modelling derived from ray tracing, we show that robust determination of disc truncation requires that the location of the coronal source is quasi-static and at a height and radius less than the truncation radius of the disc. Robust spin measurements require that at least part of the corona lies less than about 10 gravitational radii above the black hole in order that the innermost regions, including the innermost stable circular orbit, are well illuminated. The width of the blurring kernel (e.g., the iron line) has a strong dependence on coronal height. These limitations may be particularly applicable at low Eddington fractions (e.g. the low/hard state and low-luminosity AGN) where the height of the corona may be relatively large, or outflowing, and tied to jet production. © 2014 The Authors.


Dauser T.,Dr Karl Remeis Observatory and Erlangen Center for Astroparticle Physics | Garcia J.,Harvard - Smithsonian Center for Astrophysics | Parker M.L.,Institute of Astronomy | Fabian A.C.,Institute of Astronomy | Wilms J.,Dr Karl Remeis Observatory and Erlangen Center for Astroparticle Physics
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2014

In many active galaxies, the X-ray reflection features from the innermost regions of the accretion disc are relativistically distorted. This distortion allows us to measure parameters of the black hole such as its spin. The ratio in flux between the direct and the reflected radiation, the so-called reflection fraction, is determined directly from the geometry and location of primary source of radiation. We calculate the reflection fraction in the lamp post geometry in order to determine its maximal possible value for a given value of black hole spin. We show that high reflection fractions in excess of two are only possible for rapidly rotating black holes, suggesting that the high spin sources produce the strongest relativistic reflection features. Using simulations we show that taking this constraint into account does significantly improve the determination of the spin values. We make software routines for the most popular X-ray data analysis packages available that incorporate these additional constraints. © 2014 The Authors.


Dauser T.,Dr Karl Remeis Observatory and Erlangen Center for Astroparticle Physics | Svoboda J.,Czech Republic Astronomical Institute | Svoboda J.,Newton Science Operations Center | Schartel N.,Newton Science Operations Center | And 6 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2012

We present the results of a 500ks long XMM-Newton observation and a 120ks long quasi-simultaneous Chandra observation of the Narrow-Line Seyfert 1 galaxy 1H0707-495 performed in 2010 September. Consistent with earlier results by Fabian et al. and Zoghbi et al., the spectrum is found to be dominated by relativistically broadened reflection features from an ionized accretion disc around a maximally rotating black hole. Even though the spectra changed between this observation and earlier XMM-Newton observations, the physical parameters of the black hole and accretion disc (i.e. spin and inclination) are consistent between both observations. We show that this reflection spectrum is slightly modified by absorption in a mildly relativistic, highly ionized outflow which changed velocity from around 0.11c to 0.18c between 2008 January and 2010 September. Alternative models, in which the spectral shape is dominated by absorption, lead to spectral fits of similar quality, however, the parameters inferred for the putative absorber are unphysical. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


Dauser T.,Dr Karl Remeis Observatory and Erlangen Center for Astroparticle Physics | Wilms J.,Dr Karl Remeis Observatory and Erlangen Center for Astroparticle Physics | Reynolds C.S.,University of Maryland University College | Brenneman L.W.,Harvard - Smithsonian Center for Astrophysics
Monthly Notices of the Royal Astronomical Society | Year: 2010

We present an extended scheme for the calculation of the profiles of emission lines from accretion discs around rotating black holes. The scheme includes discs with angular momenta which are parallel and antiparallel with respect to the black hole's angular momentum, as both configurations are assumed to be stable. We discuss line shapes for such discs and present a code for modelling observational data with this scheme in X-ray data analysis programs. Based on a Green's function approach, an arbitrary radius dependence of the disc emissivity and arbitrary limb-darkening laws can be easily taken into account, while the amount of pre-computed data is significantly reduced with respect to other available models. © 2010 The Authors. Journal compilation © 2010 RAS.


Garcia J.A.,Harvard - Smithsonian Center for Astrophysics | Steiner J.F.,Harvard - Smithsonian Center for Astrophysics | McClintock J.E.,Harvard - Smithsonian Center for Astrophysics | Remillard R.A.,Massachusetts Institute of Technology | And 2 more authors.
Astrophysical Journal | Year: 2015

We analyze simultaneously six composite RXTE spectra of GX 339-4 in the hard state comprising 77 million counts collected over 196 ks. The source spectra are ordered by luminosity and span the range 1.6%-17% of the Eddington luminosity. Crucially, using our new tool pcacorr, we re-calibrate the data to a precision of 0.1%, an order of magnitude improvement over all earlier work. Using our advanced reflection model relxill, we target the strong features in the component of emission reflected from the disk, namely, the relativistically broadened Fe K emission line, the Fe K edge, and the Compton hump. We report results for two joint fits to the six spectra: For the first fit, we fix the spin parameter to its maximal value (a∗ = 0.998) and allow the inner disk radius Rin to vary. Results include (i) precise measurements of Rin, with evidence that the disk becomes slightly truncated at a few percent of Eddington and (ii) an order-of-magnitude swing with luminosity in the high energy cutoff, which reaches >890 keV at our lowest luminosity. For the second fit, we make the standard assumption in estimating spin that the inner edge of the accretion disk is located at the innermost stable circular orbit (Rin = RISCO) and find a∗ = 0.95+0.003 -0.05(90% confidence, statistical). For both fits, and at the same level of statistical confidence, we estimate that the disk inclination is i = 48° ± 1° and that the Fe abundance is super-solar, AFe = 5 ± 1. © 2015. The American Astronomical Society. All rights reserved.


Dauser T.,Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics | Garcia J.,Harvard - Smithsonian Center for Astrophysics | Wilms J.,Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics
Astronomische Nachrichten | Year: 2016

Measuring relativistic reflection is an important tool to study the innermost regions of the an accreting black hole system. In the following we present a brief review on the different aspects contributing to the relativistic reflection. The combined approach is for the first time incorporated in the new "relxill" model. The advantages of this more self-consistent approach are briefly summarized. A special focus is put on the new definition of the intrinsic reflection fraction in the lamp post geometry, which allows to draw conclusions about the primary source of radiation in these system. Additionally the influence of the high energy cutoff of the primary source on the reflection spectrum is motivated, revealing the remarkable capabilities of constraining Ecut by measuring relativistic reflection spectra from NuSTAR, preferably with lower energy coverage. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Garcia J.A.,Harvard - Smithsonian Center for Astrophysics | Dauser T.,Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics | Steiner J.F.,Harvard - Smithsonian Center for Astrophysics | McClintock J.E.,Harvard - Smithsonian Center for Astrophysics | And 3 more authors.
Astrophysical Journal Letters | Year: 2015

The fundamental parameters describing the coronal spectrum of an accreting black hole are the slope Γ of the power-law continuum and the energy Ecut at which it rolls over. Remarkably, this latter parameter can be accurately measured for values as high as 1 MeV by modeling the spectrum of X-rays reflected from a black hole accretion disk at energies below 100 keV. This is possible because the details in the reflection spectrum, rich in fluorescent lines and other atomic features, are very sensitive to the spectral shape of the hardest coronal radiation illuminating the disk. We show that by fitting simultaneous NuSTAR (3-79 keV) and low-energy (e.g., Suzaku) data with the most recent version of our reflection model relxill one can obtain reasonable constraints on Ecut at energies from tens of keV up to 1 MeV, for a source as faint as 1 mCrab in a 100 ks observation. © 2015. The American Astronomical Society. All rights reserved..

Loading Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics collaborators
Loading Dr Karl Remeis Observatory And Erlangen Center For Astroparticle Physics collaborators