A number of recent lines of evidence point toward the presence of hot, outflowing plasma from the central regions of compact Galactic and extragalactic X-ray sources. In addition, it has long been noted that many of these sources exhibit an ``excess'' continuum component above ~10 keV, usually attributed to Compton reflection from a static medium. Motivated by these facts, as well as by recent observational constraints on the Compton reflection models, specifically apparently discrepant variability timescales for line and continuum components in some cases, we consider possible effects of outflowing plasma on the high-energy continuum spectra of accretion-powered compact objects. We present a general formulation for photon downscattering diffusion that includes recoil and Comptonization effects due to divergence of the flow. We then develop an analytical theory for the spectral formation in such systems that allows us to derive formulae for the emergent spectrum. Finally, we perform the analytical model fitting on several Galactic X-ray binaries. Objects that have been modeled with high-covering-fraction Compton reflectors, such as GS 1353-64, are included in our analysis. In addition, Cyg X-3, which is widely believed to be characterized by dense circumstellar winds with temperature of the order of 106 K, provides an interesting test case. Data from INTEGRAL and RXTE covering the ~3-300 keV range are used in our analysis. We further consider the possibility that the widely noted distortion of the power-law continuum above 10 keV may in some cases be explained by these spectral softening effects.
Downscattering Due to Wind Outflows in Compact X-Ray Sources: Theory and Interpretation
TITARCHUK, Lev;
2005
Abstract
A number of recent lines of evidence point toward the presence of hot, outflowing plasma from the central regions of compact Galactic and extragalactic X-ray sources. In addition, it has long been noted that many of these sources exhibit an ``excess'' continuum component above ~10 keV, usually attributed to Compton reflection from a static medium. Motivated by these facts, as well as by recent observational constraints on the Compton reflection models, specifically apparently discrepant variability timescales for line and continuum components in some cases, we consider possible effects of outflowing plasma on the high-energy continuum spectra of accretion-powered compact objects. We present a general formulation for photon downscattering diffusion that includes recoil and Comptonization effects due to divergence of the flow. We then develop an analytical theory for the spectral formation in such systems that allows us to derive formulae for the emergent spectrum. Finally, we perform the analytical model fitting on several Galactic X-ray binaries. Objects that have been modeled with high-covering-fraction Compton reflectors, such as GS 1353-64, are included in our analysis. In addition, Cyg X-3, which is widely believed to be characterized by dense circumstellar winds with temperature of the order of 106 K, provides an interesting test case. Data from INTEGRAL and RXTE covering the ~3-300 keV range are used in our analysis. We further consider the possibility that the widely noted distortion of the power-law continuum above 10 keV may in some cases be explained by these spectral softening effects.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
