Suchergebnisse

We present an analysis of the X-ray spectra of the young, Crab-like pulsar PSR B1509–58 (pulse period P ~ 151ms) observed by RXTE over 14 years since the beginning of the mission in 1996. The uniform dataset is especially well suited for studying the stability of the spectral parameters over time as well as for determining pulse phase resolved spectral parameters with high significance. The phase averaged spectra as well as the resolved spectra can be well described by an absorbed power law.

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.

The eROSITA instrument on board the Russian Spectrum Roentgen Gamma spacecraft, which will be launched in 2013,will conduct an all sky survey in X-rays. A main objective of the survey is to observe galaxy clusters in order to constrain cosmological parameters and to obtain further knowledge about dark matter and dark energy. For the simulation of the eROSITA survey we present a Monte-Carlo code generating a mock catalogue of galaxy clusters distributed accordingto the mass function of [1]. The simulation generates the celestial coordinates as well as the cluster mass and redshift. From these parameters, the observed intensity and angular diameter are derived. These are used to scale Chandra cluster images as input for the survey-simulation.

GRS 1758–258 is the least studied of the three persistent black hole X-ray binaries in our Galaxy. It is also one of only two known black hole candidates, including all black hole transients, which shows a decrease of its 3-10 keV flux when entering the thermally dominated soft state, rather than an increase.We present the spectral evolution of GRS 1758–258 from RXTE-PCA observations spanning a time of about 11 years from 1996 to 2007. During this time, seven dim soft states are detected. We also consider INTEGRAL monitoring observations of the source and compare the long-term behavior to that of the bright persistent black hole X-ray binary Cygnus X-1. We discuss the observed state transitions in the light of physical scenarios for black hole transitions.

INTEGRAL is one of the few instruments capable of detecting X-rays above 20 keV. It is therefore in principle well suited for studying X-ray variability in this regime. Because INTEGRAL uses coded mask instruments for imaging, the reconstruction of light curves of X-ray sources is highly non-trivial. We present results from a comparison of two commonly employed algorithms, which primarily measure flux from mask deconvolution (ii_lc_extract) and from calculating the pixel illuminated fraction (ii_light). Both methods agree well for timescales above about 10 s, the highest time resolution for which image reconstruction is possible. For higher time resolution, ii light produces meaningful results, although the overall variance of the lightcurves is not preserved.

<p>Parallel computing and steadily increasing computation speed have led to a new tool for analyzing multiple datasets and datatypes: fitting several datasets simultaneously. With this technique, physically connected parameters of individual data can be treated as a single parameter by implementing this connection directly into the fit. We discuss the terminology, implementation, and possible issues of simultaneous fits based on the Interactive Spectral Interpretation System (ISIS) X-ray data analysis tool. While all data modeling tools in X-ray astronomy in principle allow data to be fitted individually from multiple data sets, the syntax used in these tools is not often well suited for this task. Applying simultaneous fits to the transient X-ray binary GRO J1008–57, we find that the spectral shape is only dependent on X-ray flux. We determine time independent parameters e.g., the folding energy E_fold, with unprecedented precision.</p>