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Eikmann W.,Dr. Karl Remeis Sternwarte Bamberg | Eikmann W.,Erlangen Center for Astroparticle Physics | Wilms J.,Dr. Karl Remeis Sternwarte Bamberg | Wilms J.,Erlangen Center for Astroparticle Physics | And 2 more authors.
Acta Polytechnica | Year: 2014

The spectral shape of an X-ray source strongly depends on the amount and distribution of the surrounding material. The spectrum of a primary source which is located in an optically thin medium with respect to Compton scattering is mainly modified by photo absorption in the lower energy range and is almost unaltered above ~10 keV. This picture changes when the source is obscured by gas exceeding hydrogen column densities of ~1024 cm-2. At this degree of absorption it is likely that photons are scattered at least twice before leaving the medium. The multiple scatterings lead to a lack of photons in the high energy range of the resulting spectrum as well as to an accumulation of photons at moderate energies forming the so-called Compton-bump. The shape of the fluorescent lines also changes since scattered line photons form several Compton-shoulders which are very prominent especially for Compton-thick sources. Using a Monte Carlo method, we demonstrate the importance of Compton scattering for high column densities. For that purpose, we compare our results with existing absorption models that do not consider Compton scattering. These calculations will be implemented in a prospective version of the tbabs absorption model including an analytic evaluation of the strength of the fluorescent lines. © Czech Technical University in Prague, 2014. Source

Schwarm F.-W.,Dr. Karl Remeis Sternwarte Bamberg | Schwarm F.-W.,Erlangen Center for Astroparticle Physics | Schonherr G.,Leibniz Institute for Astrophysics Potsdam | Kuhnel M.,Dr. Karl Remeis Sternwarte Bamberg | And 3 more authors.
EPJ Web of Conferences | Year: 2014

X-ray binary systems consisting of a mass donating optical star and a highly magnetized neutron star, under the right circumstances, show quantum mechanical absorption features in the observed spectra called cyclotron resonant scattering features (CRSFs). We have developed a simulation to model CRSFs using Monte Carlo methods. We calculate Green's tables which can be used to imprint CRSFs to arbitrary X-ray continua. Our simulation keeps track of scattering parameters of individual photons, extends the number of variable parameters of previous works, and allows for more flexible geometries. Here we focus on the influence of bulk velocity of the accreted matter on the CRSF line shapes and positions. © 2014 Owned by the authors. Source

Kreykenbohm I.,Dr. Karl Remeis Sternwarte Bamberg | Kreykenbohm I.,Erlangen Center for Astroparticle Physics | Furst F.,Dr. Karl Remeis Sternwarte Bamberg | Furst F.,Erlangen Center for Astroparticle Physics | And 8 more authors.
Acta Polytechnica | Year: 2011

We present a detailed spectral and timing analysis of the High Mass X-ray Binary (HMXB) 4U 1909+07 with INTEGRAL and RXTE. 4U1909+07 is a persistent accreting X-ray pulsar with a period of approximately 605 s. The period changes erratically consistent with a random walk expected for a wind accreting system. INTEGRAL detects the source with an average of 2.4 cps (corresponding to 15mCrab), but sometimes exhibits flaring activity up to 50 cps (i.e. 300mCrab). The strongly energy dependent pulse profile shows a double peaked structure at low energies and only a single narrow peak at energies above 20 keV. The phase averaged spectrum is well described by a powerlaw modified at higher energies by an exponential cutoff and photoelectric absorption at low energies. In addition at 6.4 keV a strong iron fluorescence line and at lower energies a blackbody component are present. We performed phase resolved spectroscopy to study the pulse phase dependence of the spectral parameters: while most spectral parameters are constant within uncertainties, the blackbody normalization and the cutoff folding energy vary strongly with phase. Source

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