distance: 2.5 kpc
Die Quellen des sanften Roentgenschimmers (Astronomie)
Der Weltraum glitzert und funkelt. Nicht nur wegen der Sterne oder der Hintergrundstrahlung. Sogar im Roentgenlicht erstrahlt er sanft in allen Richtungen. Was bislang als ein unerklaerliches diffuses Leuchten die Astronomen verwirrt hat, entpuppt sich bei genauerer Betrachtung mit dem Satelliten Chandra als Leuchtfeuer von unzaehligen Schwarzen Loechern, die ueber den ganzen Himmel verstreut sind. Einige davon sind so weit entfernt, dass wir von ihnen bislang kein Licht im sichtbaren Spektralbereich empfangen haben.
Specific questions to be adressed are: 1. The origin of the hard X-ray spectra in Active Galactic Nuclei and galactic Black Hole Candidates. 2. The origin of the strong time variability observed in almost all accreting compact objects. There are many forms of Variability (over a large range of time scales) and one can not expect to explain all of them with a single model since their causes may be very different. Main targets are those forms of variability that are related directly to the formation of the X-ray spectrum, and those that have their origin in the interaction between the accretion disk and the magnetosphere of the accreting object. 3. The conditions that regulate the production of a jet by a compact object or protostar.
Global theory of Balbus-Hawley instability
According to the Rayleigh criterion hydrodynamic turbulence does not arise in Keplerian disks. Although magnetic fields are known to suppress the turbulence, numerical supercomputer experiments more and more reveal a magnetic origin of the turbulent instability. With the well-known formulations of dynamo theory we have computed the relevant amplitude of the magnetic fields in order to produce the turbulence. Only the interplay of non rigid rotation and (weak) magnetic field causes the desired instability.
Nature 404, 459 - 464 (2000)
Resolving the extragalactic hard X-ray background
R. F. MUSHOTZKY, L. L. COWIE, A. J. BARGER & K. A. ARNAUD
The origin of the hard (2-10 keV) X-ray background has been a mystery for over 35 years. Most of the soft
X-ray background has been resolved into individual sources (mainly quasars), but these sources do not have
the spectral energy distribution required to match the spectrum of the X-ray background as a whole. Here we
report the results of a deep survey, using the Chandra satellite, in which the detected hard X-ray sources
account for at least 75 per cent of the hard X-ray background. The mean X-ray spectral energy distribution of
these sources is in good agreement with that of the background. Moreover, most of those hard X-ray sources
are associated unambiguously with either the nuclei of otherwise normal bright galaxies, or with optically faint
sources. The latter could be active nuclei in dust-enshrouded galaxies or a population of quasars at extremely
The short timescale bursts of Cyg X-1 in the high and transitional states, Feng Yu-xin, Chen Li, Li Ti-pei, Chinese Astronomy and Astrophysics 23 1999 423 -- 434
The X-ray power density spectrum of Cyg X-1 C. Li, F. Yu-xin, L. Ti-pei, L. Zong-wei, Chinese Astronomy and Astrophysics 24 2000 pp 159-168
The radial temperature profile in the inner region of a black-hole accretion disk,
Ding-xiong Wang, Chinese Astronomy and Astrophysics 24 2000 13 -- 22
Wind driven accretion
Wind driven accretion
Hard X-ray Emission From Low-Mass X-ray Binaries
THE INTERPLAY BETWEEN PERIODIC, CYCLIC AND STOCHASTIC VARIABILITY IN SELECTED AREAS OF THE HR DIAGRAM, University of Brussels on 22-24 July 2002.
IAU Symposium No.214: High Energy Processes and Phenomena in Astrophysics, 5-10 August, 2002 Suzhou, China
Chinese Astronomy and Astrophysics Volume 25, Issue 4
The time lag of high-energy photons of Cyg X-1 in hard state J.-l. Qu, T.-p. Li pp 416-424
The time lag between hard and soft X-rays is an important aspect of the study of high-energy emission. Fourier cross spectrum, often used in calculating the time lag, is unable to measure statistically significant fast light variation above Fourier frequency 30 Hz from the measurements of Cyg X-1. The method of cross correlation function in time domain, developed by Li Ti-pei, can be effectively used in measuring time lags on different time scales. Using Li's method we discuss the properties of the time lag of high-energy photons of Cyg X-1 in hard state at different times. The results show that there is a significant time lap on short times scales (< 0.1 s). We confront different models of hard-state Cygnus X-1 with the observed time lag.