Dr. Karl Remeis Sternwarte

Bamberg, Germany

Dr. Karl Remeis Sternwarte

Bamberg, Germany
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Barragan L.,Dr. Karl Remeis Sternwarte | Wilms J.,Dr. Karl Remeis Sternwarte | Pottschmidt K.,University of Maryland Baltimore County | Pottschmidt K.,NASA | And 4 more authors.
AIP Conference Proceedings | Year: 2010

IGR J16318-4848 is the first example, and probably the most extreme case, of a new class of highly absorbed X-ray binaries that has been discovered by the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) in the last years. We report on the analysis of the first joint Suzaku/INTEGRAL observation of this source, and also on the detection of 1RXS J163120.0-484325 during our observation. © 2010 American Institute of Physics.

Furst F.,California Institute of Technology | Muller C.,Radboud University Nijmegen | Muller C.,University of Würzburg | Madsen K.K.,California Institute of Technology | And 32 more authors.
Astrophysical Journal | Year: 2016

We present simultaneous XMM-Newton and Nuclear Spectroscopic Telescope Array (NuSTAR) observations spanning 3-78 keV of the nearest radio galaxy, Centaurus A (Cen A). The accretion geometry around the central engine in Cen A is still debated, and we investigate possible configurations using detailed X-ray spectral modeling. NuSTAR imaged the central region of Cen A with subarcminute resolution at X-ray energies above 10 keV for the first time, but found no evidence for an extended source or other off-nuclear point sources. The XMM-Newton and NuSTAR spectra agree well and can be described with an absorbed power law with a photon index Γ = 1.815 ±0.005 and a fluorescent line in good agreement with literature values. The spectrum does not require a high-energy exponential rollover, with a constraint of Efold > 1 MeV. A thermal Comptonization continuum describes the data well, with parameters that agree with values measured by INTEGRAL, in particular an electron temperature kTe between ≈100-300 keV and seed photon input temperatures between 5 and 50 eV. We do not find evidence for reflection or a broad iron line and put stringent upper limits of R lt; 0.01 on the reflection fraction and accretion disk illumination. We use archival Chandra data to estimate the contribution from diffuse emission, extra-nuclear point sources, and the outer X-ray jet to the observed NuSTAR and XMM-Newton X-ray spectra and find the contribution to be negligible. We discuss different scenarios for the physical origin of the observed hard X-ray spectrum and conclude that the inner disk is replaced by an advection-dominated accretion flow or that the X-rays are dominated by synchrotron self-Compton emission from the inner regions of the radio jet or a combination thereof. © 2016. The American Astronomical Society. All rights reserved..

Caballero I.,CEA Saclay Nuclear Research Center | Kretschmar P.,European Space Agency | Pottschmidt K.,NASA | Santangelo A.,University of Tübingen | And 14 more authors.
AIP Conference Proceedings | Year: 2010

A new outburst of the Be/X-ray binary system A0535+26 took place in August 2009. It is the fourth in a series of normal outbursts that have occurred around the periastron passage of the source, but is unusual by starting at an earlier orbital phase and by presenting a peculiar double-peaked light curve. TOO observations have been performed with INTEGRAL, RXTE and Suzaku. First results of these observations are presented, with special emphasis on the cyclotron lines present in the X-ray spectrum of the source, as well as in the pulse period and energy dependent pulse profiles of the source. © 2010 American Institute of Physics.

Bozzo E.,University of Geneva | Stella L.,National institute for astrophysics | Van Der Klis M.,University of Amsterdam | Watts A.,University of Amsterdam | And 6 more authors.
EPJ Web of Conferences | Year: 2014

LOFT, the Large Observatory For X-ray Timing, is one of five ESA M3 candidate missions. It will address the Cosmic Vision theme: "Matter under Extreme Conditions". By coupling for the first time a huge collecting area for the detection of X-ray photons with CCD-quality spectral resolution (15 times bigger in area than any previously flown X-ray instrument and >100 times bigger for spectroscopy than any similar-resolution instrument), the instruments onboard LOFT have been designed to (i) determine the properties of ultradense matter by reconstructing its Equation of State through neutron star mass and radius measurements of unprecedented accuracy; (ii) measure General Relativity effects in the strong field regime in the stationary spacetimes of neutron stars and black holes of all masses down to a few gravitational radii. Besides the above two themes, LOFT's observations will be devoted to "observatory science", providing new insights in a number of research fields in high energy astrophysics (e.g. Gamma-ray Bursts). The assessment study phase of LOFT, which ended in September 2013, demonstrated that the mission is low risk and the required Technology Readiness Level can be easily reached in time for a launch by the end of 2022. © 2014 Owned by the authors.

Svoboda J.,Czech Republic Astronomical Institute | Beuchert T.,Dr. Karl Remeis Sternwarte | Guainazzi M.,European Space Agency | Longinotti A.L.,European Space Agency | And 3 more authors.
Astronomy and Astrophysics | Year: 2015

Context. Fairall 51 is a polar-scattered Seyfert 1 galaxy, a type of active galaxy believed to represent a bridge between unobscured type-1 and obscured type-2 objects. Fairall 51 has shown complex and variable X-ray absorption, but little is known about its origin. Aims. In our research, we observed Fairall 51 with the X-ray satellite Suzaku in order to constrain a characteristic time scale of its variability. Methods. We performed timing and spectral analysis of four observations separated by 1.5, 2, and 5.5 day intervals. Results. We found that the 0.5-50 keV broadband X-ray spectra are dominated by a primary power-law emission (with the photon index ~2). This emission is affected by at least three absorbers with different ionisations (log ξ ≈ 1-4). The spectrum is shaped further by a reprocessed emission, possibly coming from two regions, the accretion disc and a more distant scattering region. The accretion disc emission is smeared by the relativistic effects, from which we measured the spin of the black hole as a ≈ 0.8 ± 0.2. We found that most of the spectral variability can be attributed to the least ionised absorber whose column density changed by a factor of two between the first (highest-flux) and the last (lowest-flux) observation. Conclusions. A week-long scale of the variability indicates that the absorber is located at the distance ≈ 0.05 pc from the centre, i.e., in the broad line region. © ESO, 2015.

Doroshenko V.,Institute For Astronomie Und Astrophysik | Santangelo A.,Institute For Astronomie Und Astrophysik | Suleimanov V.,Institute For Astronomie Und Astrophysik | Staubert R.,Institute For Astronomie Und Astrophysik | And 5 more authors.
AIP Conference Proceedings | Year: 2010

The angular momentum of matter accreting onto the neutron star produces significant spin-up torque. Effective braking mechanism must exist to balance it in order to explain the existence of slowly-rotating X-ray pulsars. The efficiency of breaking steeply decreases with the rotational frequency and the magnetic field strength. Slowly rotating sources like GX 301-2 must therefore be highly magnetized (B∼1014G), which is in apparent contradiction with the field estimate from the position of a cyclotron line observed in GX 301-2 (B∼3×1012G). We suggest that this contradiction may be resolved if the line forming region resides in an accretion column of significant height [1]. We investigate this hypothesis using INTEGRAL and BATSE observations and conclude, that the field at the top of the column shall be weak enough to explain the observed cyclotron line energy. © 2010 American Institute of Physics.

Przybilla N.,Dr. Karl Remeis Sternwarte | Nieva M.-F.,Dr. Karl Remeis Sternwarte | Nieva M.-F.,Max Planck Institute for Astrophysics | Butler K.,Universitatssternwarte
Journal of Physics: Conference Series | Year: 2011

It is generally accepted that the atmospheres of cool/lukewarm stars of spectral types A and later are described well by LTE model atmospheres, while the O-type stars require a detailed treatment of NLTE effects. Here model atmosphere structures, spectral energy distributions and synthetic spectra computed with ATLAS9/SYNTHE and TLUSTY/SYNSPEC, and results from a hybrid method combining LTE atmospheres and NLTE line-formation with DETAIL/SURFACE are compared. Their ability to reproduce observations for effective temperatures between 15 000 and 35 000 K are verified. Strengths and weaknesses of the different approaches are identified. Recommendations are made as to how to improve the models in order to derive unbiased stellar parameters and chemical abundances in future applications, with special emphasis on Gaia science.

Doroshenko V.,Institute For Astronomie Und Astrophysik | Santangelo A.,Institute For Astronomie Und Astrophysik | Kreykenbohm I.,Dr. Karl Remeis Sternwarte | Kreykenbohm I.,Erlangen Center for Astroparticle Physics | Doroshenko R.,Institute For Astronomie Und Astrophysik
Astronomy and Astrophysics | Year: 2012

We present an analysis of the spectral properties of the peculiar X-ray pulsar X Per based on INTEGRAL observations. We show that the source exhibits an unusually hard spectrum and is confidently detected by ISGRI up to more than 100 keV. We find that two distinct components may be identified in the broadband 4-200 keV spectrum of the source. We interpret these components as the result of thermal and bulk Comptonization in the vicinity of the neutron star and describe them with several semi-phenomenological models. The previously reported absorption feature at ≈30a keV is not required in the proposed scenario and therefore its physical interpretation must be taken with caution. We also investigated the timing properties of the source in the framework of existing torque theory, concluding that the observed phenomenology can be consistently explained if the magnetic field of the neutron star is ∼10 14G. © 2012 ESO.

Nieva M.-F.,Max Planck Institute for Astrophysics | Przybilla N.,Dr. Karl Remeis Sternwarte | Irrgang A.,Dr. Karl Remeis Sternwarte
Journal of Physics: Conference Series | Year: 2011

The derivation of high precision/accuracy parameters and chemical abundances of massive stars is of utmost importance to the fields of stellar evolution and Galactic chemical evolution. We concentrate on the study of OB-type stars near the main sequence and their evolved progeny, the BA-type supergiants, covering masses of ∼6 to 25 solar masses and a range in effective temperature from ∼8000 to 35 000 K. The minimization of the main sources of systematic errors in the atmospheric model computation, the observed spectra and the quantitative spectral analysis play a critical role in the final results. Our self-consistent spectrum analysis technique employing a robust non-LTE line formation allows precise atmospheric parameters of massive stars to be derived, achieving 1σ-uncertainties as low as 1% in effective temperature and ∼0.05-0.10 dex in surface gravity. Consequences on the behaviour of the chemical elements carbon, nitrogen and oxygen are discussed here in the context of massive star evolution and Galactic chemical evolution, showing tight relations covered in previous work by too large statistical and systematic uncertainties. The spectral analysis of larger star samples, like from the upcoming Gaia-ESO survey, may benefit from these findings.

Doroshenko V.,Institute For Astronomie Und Astrophysik | Suchy S.,University of California at San Diego | Santangelo A.,Institute For Astronomie Und Astrophysik | Staubert R.,Institute For Astronomie Und Astrophysik | And 7 more authors.
Astronomy and Astrophysics | Year: 2010

We present the analysis of RXTE monitoring data obtained during the 2009 January outburst of the hard X-ray transient 1A 1118-61. Using these observations the broadband (3.5-120 keV) spectrum of the source was measured for the first time ever. We have found that the broadband continuum spectrum of the source is similar to other accreting pulsars and is well described by several conventionally used phenomenological models. We have discovered that regardless of the applied continuum model, a prominent broad absorption feature at ∼55 keV is observed. We interpret this feature as a cyclotron resonance scattering feature (CRSF). The observed CRSF energy is one of the highest known and corresponds to a magnetic field of B ∼ 4.8 × 1012 G in the scattering region. Our data also indicate the presence of an iron emission line presence that has not been previously reported for 1A 1118-61. Timing properties of the source, including a strong spin-up, were found to be similar to those observed by CGRO/BATSE during the previous outburst, but the broadband capabilities of RXTE reveal a more complicated energy dependency of the pulse-profile. © 2010 ESO.

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