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Title: Black Hole Accretion and X-Ray Variability in AGN

Abstract

Active Galactic Nuclei (AGN) have very luminous centers which are so bright that the surrounding stars can not adequately account for the energy emission of AGN. One of the most accepted explanations for this energy release is black hole accretion. These black holes accrete near by gas and dust, and as a result gravitational potential is converted to energy which is released. In order to probe the accretion mechanism which lies close to the black hole, short time scale X-ray variability is analyzed. The very short time scale variability will increase understanding of the processes that occur in the heart of galaxies. Data from the ASCA X-ray telescope was reduced and analyzed using the programs FTOOLS, XSELCT, and ASCASCREEN. Light curves and event lists were generated for long term observations of different AGN which were sent to collaborators for further analysis using the event time arrivals. The analysis will compare accretion and jet dominated AGN and will provide use with an understanding of how short scale time variability can relate to the mechanism very close to black holes buried within AGN.

Authors:
Publication Date:
Research Org.:
Stanford Linear Accelerator Center, Menlo Park, CA (US)
Sponsoring Org.:
USDOE Office of Science (US)
OSTI Identifier:
833107
Report Number(s):
SLAC-TN-04-053
TRN: US200430%%1165
DOE Contract Number:
AC03-76SF00515
Resource Type:
Technical Report
Resource Relation:
Other Information: PBD: 3 Sep 2004
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; BLACK HOLES; GALAXIES; NUCLEI; PROBES; STARS; TELESCOPES

Citation Formats

Vollrath, Z. Black Hole Accretion and X-Ray Variability in AGN. United States: N. p., 2004. Web. doi:10.2172/833107.
Vollrath, Z. Black Hole Accretion and X-Ray Variability in AGN. United States. doi:10.2172/833107.
Vollrath, Z. Fri . "Black Hole Accretion and X-Ray Variability in AGN". United States. doi:10.2172/833107. https://www.osti.gov/servlets/purl/833107.
@article{osti_833107,
title = {Black Hole Accretion and X-Ray Variability in AGN},
author = {Vollrath, Z.},
abstractNote = {Active Galactic Nuclei (AGN) have very luminous centers which are so bright that the surrounding stars can not adequately account for the energy emission of AGN. One of the most accepted explanations for this energy release is black hole accretion. These black holes accrete near by gas and dust, and as a result gravitational potential is converted to energy which is released. In order to probe the accretion mechanism which lies close to the black hole, short time scale X-ray variability is analyzed. The very short time scale variability will increase understanding of the processes that occur in the heart of galaxies. Data from the ASCA X-ray telescope was reduced and analyzed using the programs FTOOLS, XSELCT, and ASCASCREEN. Light curves and event lists were generated for long term observations of different AGN which were sent to collaborators for further analysis using the event time arrivals. The analysis will compare accretion and jet dominated AGN and will provide use with an understanding of how short scale time variability can relate to the mechanism very close to black holes buried within AGN.},
doi = {10.2172/833107},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Fri Sep 03 00:00:00 EDT 2004},
month = {Fri Sep 03 00:00:00 EDT 2004}
}

Technical Report:

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  • This work discusses a black hole accretion disk dynamo model for Active Galactic Nuclei (AGN) sources of the cosmic X-ray and ..gamma.. ray backgrounds which involves both thermal and nonthermal accretion disk processes around greater than or equal to 10/sup 8/M/sub sun/ Kerr black holes. Before black hole spin-up to the Kerr metric state, the large value of the compactness parameter L(luminosity)/r(size of emitting region) > 10/sup 30/erg/cm-sec associated with the L/L/sub Edd/ less than or equal to l luminosity ratio in Precursor Active Galaxies (PAG) suppresses all nonthermal emission mechanisms. In this PAG state the resulting emission is predominantlymore » thermal and is due to Comptonization of soft photons by an electron-positron plasma, generated within the hot accretion disk region by ..gamma.. + ..gamma.. reversible e+/- processes in the transrelativistic regime. While the underlying plasma in the PAG accretion disk hot inner region may be optically thin initially, the overall effect of the copious ..gamma.. + ..gamma.. reversible e+/- generated electron-positron plasma is to push the overall optical depth to tau greater than or equal to 1. This has two main effects: a) it causes the resulting Comptonized spectrum of X-radiation from PAG to be associated with a flat spectral index comparable to that of the residual Cosmic X-ray Background (CXB), and b) the copious ..gamma.. + ..gamma.. reversible e+/- within the hot accretion disk region play the role of a phase transition thermostat, and act to maintain the temperature of the hot inner region at greater than or equal to 109/sup 0/K. 16 references.« less
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  • The specific angular momentum of the gas captured by a black hole in a detached binary system would be quite small. An accretion disk emitting x rays cannot form around such a black hole, but fluctuations in the stellar-wind velocity and density might produce transient disks and a high degree of x-ray variability.
  • We present an energy dependent X-ray variability study of the 2010 outburst of the black hole X-ray binary MAXI J1659–152 with the Swift X-ray Telescope (XRT). The broadband noise components and the quasi-periodic oscillations (QPO) observed in the power spectra show a strong and varied energy dependence. Combining Swift XRT data with data from the Rossi X-ray Timing Explorer, we report, for the first time, an rms spectrum (fractional rms amplitude as a function of energy) of these components in the 0.5–30 keV energy range. We find that the strength of the low-frequency component (<0.1 Hz) decreases with energy, contrarymore » to the higher frequency components (>0.1 Hz) whose strengths increase with energy. In the context of the propagating fluctuations model for X-ray variability, we suggest that the low-frequency component originates in the accretion disk (which dominates emission below ∼2 keV) and the higher frequency components are formed in the hot flow (which dominates emission above ∼2 keV). As the properties of the QPO suggest that it may have a different driving mechanism, we investigate the Lense–Thirring precession of the hot flow as a candidate model. We also report on the QPO coherence evolution for the first time in the energy band below 2 keV. While there are strong indications that the QPO is less coherent at energies below 2 keV than above 2 keV, the coherence increases with intensity similar to what is observed at energies above 2 keV in other black hole X-ray binaries.« less
  • A calibration is made for the correlation between the X-ray Variability Amplitude (XVA) and black hole (BH) mass. The correlation for 21 reverberation-mapped Active Galactic Nuclei (AGNs) appears very tight, with an intrinsic dispersion of 0.20 dex. The intrinsic dispersion of 0.27 dex can be obtained if BH masses are estimated from the stellar velocity dispersions. We further test the uncertainties of mass estimates from XVAs for objects that have been observed multiple times with good enough data quality. The results show that the XVAs derived from multiple observations change by a factor of 3. This means that BH massmore » uncertainty from a single observation is slightly worse than either reverberation-mapping or stellar velocity dispersion measurements; however, BH mass estimates with X-ray data only can be more accurate if the mean XVA value from more observations is used. With this calibrated relation, the BH mass and accretion rate may be determined for a large sample of AGNs with the planned International X-ray Observatory mission. Proper interpretation of the first AGN X-ray quasi-periodic oscillation (QPO), seen in the Seyfert galaxy RE J1034+396, depends on its BH mass, which is not currently known very well. Applying this relation, the BH mass of RE J1034+396 is found to be 4{sup +3}{sub -2} x 10{sup 6} M{sub sun}. The high end of the mass range follows the relationship between the 2f{sub 0} frequencies of high-frequency QPO and the BH masses derived from the Galactic X-ray binaries. We also calculate the high-frequency constant C = 2.37 M{sub sun} Hz{sup -1} from 21 reverberation-mapped AGNs. As suggested by Gierlinski et al., M{sub BH} = C/C{sub M}, where C{sub M} is the high-frequency variability derived from XVA. Given the similar shape of power-law dominated X-ray spectra in ultra-luminous X-ray sources (ULXs) and AGNs, this can be applied to BH mass estimates of ULXs. We discuss the observed QPO frequencies and BH mass estimates in the ULXs M82 X-1 and NGC 5408 X-1 and favor ULXs as intermediate mass BH systems.« less