1,326 research outputs found
Bernoulli equation and the nonexistence of maximal jets
We discuss the idea of maximal jets introduced by Falcke & Biermann in 1995.
According to it, the maximum possible jet power in its internal energy equals
the kinetic power in its rest mass. We show this result is incorrect because of
an unfortunate algebraic mistake.Comment: A&A, in pres
A study of spectra of Cyg X-3 observed by BeppoSAX
We model the ~1-200 keV spectra of Cygnus X-3 observed by BeppoSAX. The
continuum, modeled by Comptonization in a hybrid plasma, is modified by the
strongly ionized plasma of the stellar wind of the Wolf-Rayet companion star.
Discrete absorption and emission spectral features are modeled with XSTAR. The
model has been applied to phase-resolved spectra in the hard and soft spectral
states.Comment: 3 pages, to appear in the Proceedings of the Conference "X-ray
Diagnostics of Astrophysical Plasmas", Cambridge, November 15-17, 2004.
Replacement: minor changes in text and acknowledgement
Thermal synchrotron radiation and its Comptonization in compact X-ray sources
We investigate thermal synchrotron radiation at semi-relativistic and
relativistic temperatures. We find an analytic expression for the
angle-averaged emission coefficient, and show that it is significantly more
accurate that those derived previously. We also present analytic approximations
to the synchrotron turnover frequency. Then, we treat Comptonization of the
synchrotron radiation, and give simple expressions for the spectral shape and
the emitted power. We also consider modifications of the above results by
bremsstrahlung. The importance of Comptonization of synchrotron radiation in
compact X-ray sources is then studied. We consider emission from hot accretion
flows and from active coronae above optically-thick accretion discs in
black-hole binaries and AGNs. Synchrotron Comptonization is found to be, in
general, negligible in luminous sources, except for those with hardest X-ray
spectra and stellar masses. Increasing the black-hole mass results in a strong
reduction of the maximum Eddington ratio possible from to this process. X-ray
spectra of intermediate-luminosity sources, e.g., low-luminosity AGNs, can be
explained by synchrotron Comptonization only in the case of hot accretion
flows. Then, bremsstrahlung emission always dominates X-ray spectra of very
weak sources. Finally, we consider weakly-magnetized neutron stars and find
that synchrotron Comptonization can account for the power-law X-ray spectra
observed in their low states.Comment: 17 pages, 17 postscript figures. Accepted to MNRA
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