INTEGRAL: science highlights and future prospects

ESA's hard X-ray and soft gamma-ray observatory INTEGRAL is covering the 3 keV to 10 MeV energy band, with excellent sensitivity during long and uninterrupted observations of a large field of view (~100 square degrees), with ms time resolution and keV energy resolution. It links the energy band of pointed soft X-ray missions such as XMM-Newton with that of high-energy gamma-ray space missions such as Fermi and ground based TeV observatories. Key results obtained so far include the first sky map in the light of the 511 keV annihilation emission, the discovery of a new class of high mass X-ray binaries and detection of polarization in cosmic high energy radiation. For the foreseeable future, INTEGRAL will remain the only observatory allowing the study of nucleosynthesis in our Galaxy, including the long overdue next nearby supernova, through high-resolution gamma-ray line spectroscopy. Science results to date and expected for the coming mission years span a wide range of high-energy astrophysics, including studies of the distribution of positrons in the Galaxy; reflection of gamma-rays off clouds in the interstellar medium near the Galactic Centre; studies of black holes and neutron stars particularly in high- mass systems; gamma-ray polarization measurements for X-ray binaries and gamma-ray bursts, and sensitive detection capabilities for obscured active galaxies with more than 1000 expected to be found until 2014. This paper summarizes scientific highlights obtained since INTEGRAL's launch in 2002, and outlines prospects for the INTEGRAL mission.Comment: 39 pages, accepted, 24 October 2011, Space Science Review

X-rays From Galactic Black Holes - Theory and Observation

Die Arbeit untersucht die Entstehung der harten Röntgenstrahlung galaktischer Schwarzlochkandidaten. Der wahrscheinlichste physikalische Prozeß, der dieses Spektrum erzeugt, ist die Comptonisierung weicher Strahlung in einem heißen Elektronenplasma, einer Akkretionsscheibenkorona. Diese entsteht wahrscheinlich als Folge hydrodynamischer Instabilitäten in einer Akkretionsscheibe. Unter Comptonisierung versteht man hierbei die Erzeugung harter Photonen durch inverse Comptonstöße an heißen Elektronen. Dabei können Photonendichten entstehen, die so groß sind, daß Photon-Photon-Paarbildungsprozesse eintreten können. Unter Verwendung nichtlinearer Monte Carlo Methoden wird das Strahlungstransportproblem in solchen Akkretionsscheibenkoronen selbstkonsistent für verschiedene Geometrien gelöst. Um genaue Parameter für die Koronen in Schwarzen Löchern zu erhalten, müssen die aus den theoretischen Rechnungen erhaltenen Spektren direkt mit Beobachtungsdaten verglichen werden. Hierzu sind Beobachtungen im Energiebereich von 1 bis 300 keV notwendig. Die Arbeit geht besonders auf eine Rossi X-ray Timing Explorer Beobachtung des galaktischen Schwarzen Loches Cygnus X-1 ein. Hier zeigt sich, daß die Akkretionsscheiben- modelle tatsächlich das Röntgenspektrum beschreiben können. Die optische Tiefe der Korona beträgt tau=2.1+/-0.1, ihre mittlere Temperatur ist kT=65.7+/-3.3 keV. Ferner kann aus dem zeitlichen Verhalten der Quelle eine koronale Größe kleiner als 25 GM/c^2 abgeleitet werden.This dissertation analyzes the generation mechanisms for the hard X-rays observed from galactic black hole candidates. The most probable physical process generating the observed spectrum is Comptonization of soft radiation in a hot electron plasma, an accretion disk corona (ADC). This corona is most probably the result of hydrodynamical instabilities in an accretion disk. 'Comptonization' means the generation of hard photons through inverse Compton collisions with hot (energetic) electrons. It is possible that the resulting photon densities are large enought that photon-photon pair-production becomes important. Using nonlinear Monte Carlo Methods we solve the radiation transport problem in such accretion disks in a selfconsistent way for several geometries. To obtain the exact physical parameters for the coronae of black holes it is necessary to compare the spectra from the theoretical computations with observational data. For this, observations in the energy range from 1 to 300 keV are necessary. This work concentrates on a Rossi X-ray Timing Explorer observation of the galactic black hole Cygnus X-1. It is shown that the accretion disk models are able to describe the observed X-ray spectrum. The optical depth of the corona is tau=2.1+/-0.1, its average temperature is kT=65.7+/-3.3 keV. Furthermore, analysis of the temporal variability of the source results in a coronal size smaller than 25 GM/c^2

Temporal Variations of Strength and Location of the South Atlantic Anomaly as Measured by RXTE

The evolution of the particle background at an altitude of ~540 km during the time interval between 1996 and 2007 is studied using the particle monitor of the High Energy X-ray Timing Experiment on board NASA's Rossi X-ray Timing Explorer. A special emphasis of this study is the location and strength of the South Atlantic Anomaly (SAA). The size and strength of the SAA are anti-correlated with the the 10.7 cm radio flux of the Sun, which leads the SAA strength by ~1 year reflecting variations in solar heating of the upper atmosphere. The location of the SAA is also found to drift westwards with an average drift rate of about 0.3 deg/yr following the drift of the geomagnetic field configuration. Superimposed to this drift rate are irregularities, where the SAA suddenly moves eastwards and where furthermore the speed of the drift changes. The most prominent of these irregularities is found in the second quarter of 2003 and another event took place in 1999. We suggest that these events are previously unrecognized manifestations of the geomagnetic jerks of the Earth's magnetic field.Comment: 21 pages, 11 figures, accepted for publication in Earth and Planetary Science Letter

X-ray monitoring of the radio and gamma-ray loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447

We present preliminary results of the X-ray analysis of XMM-Newton and Swift observations as part of a multi-wavelength monitoring campaign in 2012 of the radio-loud narrow line Seyfert 1 galaxy PKS 2004-447. The source was recently detected in gamma-rays by Fermi/LAT among only four other galaxies of that type. The 0.5-10 keV X-ray spectrum is well-described by a simple absorbed powerlaw (photon index ~ 1.6). The source brightness exhibits variability on timescales of months to years with indications for spectral variability, which follows a 'bluer-when-brighter' behaviour, similar to blazars.Comment: Proceedings for the 'Jet 2013' conference. Includes 3 pages, 3 figure

X-RAY TRANSMISSION AND REFLECTION THROUGH A COMPTON-THICK MEDIUM VIA MONTE-CARLO SIMULATIONS

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