Comptonizing Plasma Research Articles

An X‐Ray Reprocessing Model of Disk Thermal Emission in Type 1 Seyfert Galaxies

Using a geometry consisting of a hot central Comptonizing plasma surrounded by a thin accretion disk, we model the optical through hard X-ray spectral energy distributions of the type 1 Seyfert galaxies NGC 3516 and NGC 7469. As in the model proposed by Poutanen, Krolik, & Ryde for the X-ray binary Cygnus X-1 and later applied to Seyfert galaxies by Zdziarski, Lubi\'nski, & Smith, feedback between the radiation reprocessed by the disk and the thermal Comptonization emission from the hot central plasma plays a pivotal role in determining the X-ray spectrum, and as we show, the optical and ultraviolet spectra as well. Seemingly uncorrelated optical/UV and X-ray light curves, similar to those which have been observed from these objects can be explained by variations in the size, shape, and temperature of the Comptonizing plasma. Furthermore, by positing a disk mass accretion rate which satisfies a condition for global energy balance between the thermal Comptonization luminosity and the power available from accretion, one can predict the spectral properties of the hard X-ray continuum above $\sim 50$ keV in type 1 Seyfert galaxies. Forthcoming measurements of the hard X-ray continuum by more sensitive hard X-ray and soft $\gamma$-ray telescopes, in conjunction with simultaneous optical, UV, and soft X-ray monitoring, will allow the mass accretion rates to be directly constrained for these sources in the context of this model.

Thermal Comptonization and Disk Thermal Reprocessing in NGC 3516

We present an application of the thermal Comptonization/disk reprocessing model recently proposed by Zdziarski, Lubiniski, and Smith. We show that the absence of strong optical variations in the presence of strong concurrent X-ray variations, similar to those found by Hubble Space Telescope (HST)/Rossi X-Ray Timing Explorer (RXTE) monitoring observations of NGC 3516, can be explained by changing the geometry of the Comptonizing plasma rather than the accretion disk itself. The total X-ray luminosity of the Comptonizing plasma must decrease as its spatial extent increases. In contrast, the disk inner radius must be roughly fixed in order not to produce optical/ultraviolet color variations stronger than observed. By including emission due to internal viscous dissipation in the disk, we can roughly match the optical and X-ray flux levels and variability amplitudes seen from NGC 3516 during the HST/RXTE campaign.

Simultaneous BeppoSAX and RXTE observations of the X-ray burst sources GX 3+1 and Ser X-1

We have obtained spectral and timing data on GX 3+1 and Ser X-1. Both sources were observed simultaneously with BeppoSAX and RXTE. The RXTE data is used to provide power spectra and colour-colour diagrams in order to constrain the state (and thus track $\dot M$) the sources are in. The BeppoSAX data provide the broad-band spectra. The spectra of both sources are reasonably well-fit using a model consisting of a disk-blackbody, a comptonized component and a Fe line, absorbed by interstellar absorption. The electron temperature (kT$_{\rm e}$) of the Comptonizing plasma is in both cases $\sim$2.5 keV. This implies that no strong high-energy tail from the Comptonized component is present in either of the sources. We discuss the similarities between these burst sources and the luminous X-ray sources located in globular clusters. We find that the spectral parameters of the comptonized component provide information about the mass-accretion rate, which agrees well with estimates from the timing and spectral variations.

Monte Carlo simulation of Comptonization in plasma accreting onto neutron stars

view Abstract Citations (2) References (9) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Monte Carlo Simulation of Comptonization in Plasma Accreting onto Neutron Stars Hanawa, Tomoyuki Abstract It is shown by Monte Carlo simulation that high-energy X-rays are produced through Compton scattering in plasma accreting onto neutron stars where the gas infalls radially. The neutron star surface is heated by the gravitational energy release of the accreting gas and radiates soft X-ray photons. The X-ray from the surface are scattered by electrons in the plasma accreting onto the star. Since the infalling velocity is nearly half light speed, the energy of the scattered X-ray changes by 50 percent. Some X-rays are scattered repeatedly between the star and the accreting gas and become high-energy X-rays. The scattered X-ray photons have a power-law spectrum in high-energy range. This model is applied to X-ray spectra of type II bursts from the rapid burster MXB 1730 - 335. Publication: The Astrophysical Journal Pub Date: January 1991 DOI: 10.1086/169584 Bibcode: 1991ApJ...366..495H Keywords: Accretion Disks; Neutron Stars; Space Plasmas; Stellar Mass Accretion; Stellar Radiation; X Rays; Compton Effect; Computational Astrophysics; Monte Carlo Method; Astrophysics; RADIATION MECHANISMS; STARS: ACCRETION; STARS: NEUTRON; X-RAYS: BURSTS full text sources ADS | data products SIMBAD (2)