Other
Scientific paper
Dec 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.9103l&link_type=abstract
American Astronomical Society, 195th AAS Meeting, #91.03; Bulletin of the American Astronomical Society, Vol. 31, p.1510
Other
Scientific paper
we report our observational, data analysis and theoretical results about the X- and gamma-ray emissions from black hole candidates (BHCs). We made multi-wavelength observations of GRS 1758-258 in August 1997. The observations revealed several properties that are important for constraining the emission model and the geometry of the accretion disk. (1) Its spectrum does not have a significant soft component. The lack of a strong soft component implies that the cold optically thick disk must be small or be mostly covered by a optically thin hot corona. (2) The spectrum has a exponential cutoff around 200 keV. This means that the hot corona is largely thermal. (3) No significant iron lines are detected. This suggests that the reprocessing of the X-ray by the cold disk is negligible. (4) The medium energy band (5 -- 10 keV) has the highest variability. We systematically studied the energy dependency of the variability for the four persistent hard X-ray sources: Cygnus X--1, GX 339--4, GRS 1758--258 and 1E 1740.7--2942. Cygnus X--1 is found to have flatter power density spectrum (PDS) shapes at higher energies, while the other three sources have energy independent PDS shapes. The energy dependency of the overall variability varies from source to source and from observation to observation. A general trend is found among the four sources that the overall variability anti-correlates with the X-ray flux. We suggest that this trend, as well as the various energy dependencies of the overall variability, can be explained by the different origins of the persistent emission and the flare emission. We also made similar studies of GRS 1915+105. We found the flat radio spectrum observed in most BHCs can be explained by a hybrid thermal-nonthermal plasma. The emission mechanisms include bremsstrahlung and gyro-synchrotron.
Böttcher Markus
Liang Edison P.
Lin Dacheng
Smith Ian A.
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