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X-ray Astronomy


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X-ray Astronomy

X-rays originate from matter under extreme conditions. These are found in accreting binary stars, the coronae of normal stars, very compact stars, accreting supermassive black holes, and the hot intergalactic medium in galaxy clusters. Our group has a (i) wide and a (ii) narrow scope: (i) We use various X-ray surveys to build complete samples of different source distributions the sky. (ii) We investigate certain X-ray emitters to understand the physical processes that lead to the emission of X-rays and the formation of broad-band spectral energy distributions. The AIP X-ray group takes part in national and international space missions such as XMM-Newton and eROSITA.


People

Name Office Phone E-Mail
(+49 331 - 7499...) (@aip.de)
Philip Ehrlich SH/231 286 pehrlich
René Heller SH/231 286 rheller
Arjen de Hoon SH/230 328 arjen
Alexey Mints SH/225 321 amints
Georg Lamer SH/225 321 glamer
Adriana Pires SH/229 321 apires
Andreas Rabitz SH/230 328 arabitz
Gabriele Schönherr LH/1-18 383 gschoenherr
Robert Schwarz SH/231 286 schwarz
Axel Schwope (Head) SH/227 232 aschwope
Ali Takey SH/230 428 atakey
Sabine Thater SH/225 321 sthater
Iris Traulsen SH/231 286 itraulsen


X-ray group Dec. 2011
from left to right: Sabine Thater, Iris Traulsen, Gabriele Schönherr, Georg Lamer, Robert Schwarz, Ali Takey, Valentina Scipione, Axel Schwope, Adriana Pires, René Heller

OLDER PICTURES (beginning 2005 at the right end)
X-ray group Dec. 2010 X-ray group Dec. 2009 X-ray group Dec. 2008 X-ray group Dec. 2007 X-ray group Dec. 2006 X-ray group Nov. 2005

FORMER MEMBERS (in alphabetical order)
Daniele Facchino, Mareike Godolt, Theodor Hamann, Valeri Hambaryan, Matthias Hoeft, Jan Kohnert, Alexander Kolodzig, Mirko Krumpe, Matthias Müller, Ada Nebot Gomez-Moran, Jose Ramirez, Matthias Schreiber, Andreas Staude, Justus Vogel

Science

X-ray Binary Stars
Cataclysmic Variables (CVs) are compact, short period, interacting binaries with a white dwarf as the primary star. Our research interest is mainly focused on systems that harbour a strongly magnetic white dwarf. Here the field is large enough (1-230 MegaGauss) to greatly modify the mass transfer from the mass donating secondary. Unlike nonmagnetic CVs the infalling material is radially channelled to a compact region, where most of the kinetic energy is released as X-ray and cyclotron emission. We use spectral and temporal information from X-ray missions like XMM-Newton to derive an accurate understanding of the complex accretion zone. In addition, we try to resolve the structure of the mass flow and the heated white dwarf involving indirect imaging techniques such as Doppler tomography, eclipse mapping and light curve modelling. Another important aspect of our work is the evolution of compact binaries. We are currently involved in a dedicated search for the progenitors of Cataclysmic Variables using the SLOAN/SEGUE-survey.
Most recent papers:
CV


Active Galactic Nuclei
Active Galactic Nuclei (AGN) are fuelled by accretion of matter onto supermassive black holes. A large part of the power generated by the accretion process is emitted as X-ray radiation. With the extended energy range and sensitivity of the X-ray telescopes on the XMM-Newton and Chandra satellites it became possible to observe also AGN which are heavily obscured by gas and dust in their surrounding medium. These absorbed AGN are thought to be responsible for the hard spectrum of the cosmic X-ray background. Our main interests are the identification and study of AGN in X-ray surveys and spectral studies of AGN with XMM-Newton. Projects include the XMM Marano field survey and contributions to the identification of the XMM serendipity surveys conducted by the XMM-Newton Survey Science Centre. Recent papers: CV


Isolated Neutron Stars
Isolated Neutron stars are a new class of soft X-ray emitters discovered by ROSAT. Their unique properties are: a soft, thermal X-ray spectrum, very little interstellar absorption, a high ratio between X-ray and optical flux, fX/fopt > 104, no signs of binarity, no magnetospheric emission, and no association with a supernova remnant. Despite the expection to find thousands of those objects in the ROSAT all-sky survey, to date only seven could be uniquely identified, now termed the Magnificent Seven.
Our group was involved in the discovery of two of them, RBS1223 and RBS1556, which were identified as bright X-ray source with no optical counterpart down to a magnitude of 25.6 in the ROSAT Bright Survey (Schwope et al. (2000), Astron. Nachr. 321, 1).
The great interest in those sources arose from the fact, that these stars offer the unique opportunity to study a neutron's star surface uncontaminated from any other emission. There is hope, to identify spectral features in their X-ray spectra which allow to derive constraints on the equation-of-state of ultradense matter.
Our main achievements:
CV


Clusters of Galaxies
Galaxy clusters are the largest gravitational bound objects known in the univere containing several tens to hundreds of galaxies. Their evolution strongly depends on various cosmoligical parameters and so they are ideal objects to stress cosmological models. As this dependency gets stronger in the higher-redshift regime, we try tho extend the sample of such objects beyond redshift z=1, which is roughly a distance of 8.5 billion lightyears. While in the optical range most likely found as a local overdensity of galaxies, the are detectable as extended sources in xrays. The XMM-Newton-archive provides a very good source to look for these extended objects and so we started a large survey relying on that archive. A pilot study was done some time ago and proved the reliability of the method to select the objects in xrays, do imaging in to different color-ranges in optical/IR so select the most likely high-redshift candidates and in a third step spectroscopically confirm their distance. This international collaboration has in combination with the Rosat deep cluster survey increased the number of known clusters with z > 1 from six to twelve. More candidates are in the queue.

In a recent study (Takey, Schwope, and Lamer 2011), we presented a catalogue of X-ray selected galaxy clusters and groups as a first release of the 2XMMi/SDSS Galaxy Cluster Survey. On this site, we present a more detailed summary of this work.
rbs


X-ray surveys
With X-ray surveys at different flux levels one builds up statistically complete samples of X-ray emitters, a necessary prerequisite for e.g. evolutionary studies. They also uncover the rare and exotic objects, worth to be followed-up individually. In the ROSAT era, we have been involved in or leading surveys for bright sources at high latitudes, in the era of XMM-Newton era we took part in XMM-SSC (Survey Science Centre) which created the most massive X-ray catalogue to date with more than 150000 entries. Many identification programs are based on this catalogue and earlier, pre-mature versions.Surveys with AIP-leadership or involvement are: xraysurvey



Projects

The AIP 70cm-Telescope
The AIP 70 cm reflector was built in 1958 and overhauled in 1994. The telescope is equipped with a cryogenic 1k x 1k CCD. Besides the training for students it is frequently used for scientific observations. Principal application is time resolved photometry of cataclysmic variable stars. 70cm_telescope

eROSITA
eROSITA (extended ROentgen Survey with an Imaging Telescope Array) is a X-ray telescope which will be build under the leadership of the MPE. It should perform the first imaging all-sky survey in the medium energy X-ray range up to 10 keV with an unprecedented spectral and angular resolution. The nature of the mysterious Dark Energy that is driving the Universe apart is one of the most exciting questions facing astronomy and physics today. It may be the vacuum energy providing the Cosmological Constant in Einstein's theory of General Relativity, or it may be a time-varying energy field. The solution could require a fundamental revolution in physics. Clusters of galaxies are the largest collapsed objects in the Universe. Their formation and evolution is dominated by gravity, i.e. Dark Matter, while their large scale distribution and number density depends on the geometry of the Universe, i.e. Dark Energy. X-ray observations of clusters provide information on the rate of expansion of the Universe, the fraction of mass in visible matter and the amplitude of primordial fluctuations that are the origin of clusters of galaxies and the whole structure of the universe. (press release (german)). eROSITA


XMM SSC
The XMM Survey Science Centre (SSC) is a consortium of eight European institutions , led by Leicester University. Within the XMM project, the SSC has responsibilities to develop science analysis software for XMM (jointly with ESA's XMM Science Operations Centre), to perform a pipe-line processing of all XMM observations, and to conduct a follow-up/identification programme for the XMM serendipitous X-ray survey. The AIP has the responsibility to provide the source detection software for the pipe-line processing of the XMM EPIC data. SSC


ROSAT Results Archive (till 2001)
The ROSAT Results Archive contains results (positions, count rates, hardness ratios, extent, and variability information) on some 100,000 objects detected in more than 5000 observations performed by ROSAT. The data have undergone a thorough screening and validation process, including an automatic screening and visual inspection of all ROSAT images. About 1700 ROSAT datasets were screened at AIP. The project was conducted in collaboration with MPE, GSFC, SAO and Leicester University. RRA


SODART (till 2000)
SODART was a high-throughput multi-mirror X-ray twin telescope of 8m focal length with changeable detectors on slides for energies between 0.1 and 20 keV for the SPECTRUM X GAMMA satellite, an international high-energy space mission under IKI (Russia) leadership. Launch was planned for 2003, but there was never a confirmation of a schedule for a firm launch date. SODART


ABRIXAS (till 2000)
ABRIXAS (A Broad-band Imaging X-ray All-sky Survey) was a small satellite mission which was planned to observe the X-ray sky for three years in the energy band 0.5-10 keV. One main goal of the project was to study the absorbed AGN population and its contribution to the X-ray background. After the succesful launch of the ABRIXAS satellite on April 28th 1999 it turned out that there was a failure in the satellite's power system. On July 1st 1999 DLR has declared that the scientific mission of ABRIXAS failed. ABRIXAS


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updated: 2011, Sep. 11 by René Heller