Constraints on Black Hole Emission Mechanisms

Details Constraints on Black Hole Emission Mechanisms Constraints on Black Hole Emission Mechanisms

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001phdt.......146m&link_type=abstract

PhD Thesis, Yale University, December 2001, 162 pages

Computer Science

2

X-Rays:Binaries, X-Rays:Individual:Cygnus X-1, X-Rays:Individual:Grs 1915+105, X-Rays:Individual:Aql X-1, Accretion Disks, Methods:Statistical

Scientific paper

This thesis concentrates on the analysis of a unique Rossi X-ray Timing Explorer(RXTE)/Oriented Scintillation Spectrometer Experiment(OSSE) data set for Cygnus X-1.
We find:
(1) Autocorrelation and cross-correlation analyses of Cyg X-1 require an active rather than a static corona and the observed hard time lags must come from coronal variations rather than light travel times,
(2) The lightcurves of Cyg X-1 and GX 339-4 show a different sense of asymmetry on long timescales than on short timescales. This requires a second process driving the long timescale variability, perhaps an energy reservoir.
(3) The hard-state X/γ-ray spectrum of Cyg X-1 is well modelled with a single corona, and is shown to have a reflection fraction substantially less than unity. Hybrid thermal/non-thermal models are preferred over pure thermal models.
(4) In the soft and transition states, the iron line of Cyg X-1 has a constant equivalent width, requiring that the line emission comes primarily from the disk/corona system, and a constant blackbody temperature, requiring that coronal changes drive the variability.
(5) The spectra of GRS 1915+105 are well fit by hybrid Comptonization models, often with large non-thermal electron fractions. Reflection features are washed out at high optical depths. Disk radii can be correctly fit with these models.
(6) The spectra of neutron star Aql X-1 can be well fit with thermal Comptonization models. Bursts are used to probe the corona in neutron stars. The state transitions occur at variable luminosities, casting doubt on propeller models.

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