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At least 595 records · Page 33
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NASA NTRS1999

Hard X-Ray Variability of the Black Hole Candidate GRO J0422+32 During its 1992 Outburst

We have studied the hard X-ray variability of the soft X-ray transient GRO J0422+32 with BATSE (Burst and Transient Source Experiment) in the 20-100 keV energy band. Our analysis covers 180 days following the first X-ray detection of the source on August 5, 1992, fully covering its primary and secondary X-ray outbursts. We compute power density spectra (PDSs) in the 20-50, 50-100, and 20-100 keV energy bands, in the frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately flat up to a break frequency, and decay as a power law above it, with index approximately 1. During the first 70 days of the X-ray outburst, the PDSs of GRO J0422+32 show a significant quasi-periodic oscillation (QPO) peak near approximately 0.2 Hz, superposed on the power-law tail. The break frequency of the PDSs obtained during the primary X-ray outburst of GRO J0422+32 occurs at 0.041 +/- 0.006 Hz; during the secondary outburst, the break is at 0.081 +/- 0.015 Hz. The power density at the break ranged between 44% and 89% / square root of Hz (20-100 keV). The canonical anticorrelation between the break frequency and the power density at the break, observed in Cyg X-1 and other BHCs in the low state, is not observed in the PDSs of GRO J0422+32. We compare our results with those of similar variability studies of Cyg X-1. The relation between the spectral slope and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of Cyg X-1; however, the relation between the hard X-ray flux and the amplitude of its variation is opposite to what has been found in Cyg X-1. Phase lags between the X-ray flux variations of GRO J0422+32 at high and low photon energies could only be derived during the first 30 days of its outburst. During this period, the variations in the 50-100 keV band lag those in the 20-50 keV energy band by an approximately constant phase difference of 0.039(3) rad in the frequency interval 0.02-0.20 Hz. The time lags of GRO J0422+32 during the first 30 days of the outburst decrease with frequency as a power law with index 0.9 for v > 0.01 Hz.

vanderHooft, F.↗
NASA NTRS1998

Hard X-Ray Variability of the Black Hole Candidate GRO J0422+32 During its 1992 Outburst

We have studied the hard X-ray variability of the soft X-ray transient GRO J0422+32 with the Burst and Transient Source Experiment (BATSE) in the 20-100 keV energy band. Our analysis covers 180 days following the first X-ray detection of the source on 1992 August 3, fully covering its primary and secondary X-ray outburst. We computed power density spectra (PDSS) in the 20-50, 50-100, and 20-100 keV energy bands., in the frequency interval 0.002-0.488 Hz. The PDSs of GRO J0422+32 are approximately flat up to a break frequency and decay as a power law above, with index about 1. During the first 70 days of the X-ray outburst, the PDSs of GRO J0422+32 show a significant QPO Peak near about 0.2 Hz, superposed on the power-law tail. The break frequency of the PDSs obtained during the primary X-ray outburst of GRO J0422+32 occurs at 0.041+/-0.006 Hz; during the secondary outburst the break is at 0.081q0.01.5 Hz. The power density at the break ranged between 44 and 89% Hz(exp -1/2) 20-100 keV). The canonical anticorrelation between the break frequency and the power density at the break, observed in Cyg X-1 and other BHCs in the low state, is not observed in the PDSs of GRO J0422+32. We compare our results with those of similar variability studies of Cyg X-1. The relation between the spectral slope and the amplitude of the X-ray variations of GRO J0422+32 is similar to that of Cyg X-1.

VanderHooft, F.↗
NASA NTRS1999

Black Hole X-Ray Nova Outburst with XTE and HST

We obtained multiwavelength coverage of the soft X-ray transient GRO J1655-40 during its 1996 outburst, using HST, RXTE, CGRO, and ground-based facilities. This outburst was qualitatively different from other SXT outbursts and from previous outbursts of this source. The onset of hard X-ray activity occurred very slowly, over several months, and was delayed relative to the soft X-ray rise. During this period, the optical fluxes declined steadily. This apparent anticorrelation is not consistent with with the standard disk instability model of SXT outbursts, nor is it expected if the optical output is dominated by reprocessed X-rays, as in persistent low-mass X-ray binaries. .

Patterson, Joseph↗
NASA NTRS1999

Self-Gravitating Fundamental Strings and Black Holes

The configuration of typically highly excited M much greater than M(sub s) which is approximately equal to alpha(prime) to the 1/2 power string states is considered as the string coupling g is adiabatically increased. The size distribution of very massive single string states is studied and the mass shift, due to a long-range gravitational, dilatonic, and axionic attraction, is estimated.

Damour, T.↗
NASA NTRS2003

Accreting Black Holes an All Out Effort

This final report lists many publications resulting from this grant. The following is a representative listing of several dozen title: (1) '1100 Days of BATSE observations of Cyg X-1', D Crary, C. Kouveliotou, J. van Paradijs, F. v.d. Hooft, B. Rubin, S. Zhang, W. Paciesas, M. Fini:er, B. Harmon, M. v.d. Klis, W.H.G. Lewin, and J. Norris, Astron. Astrophys. Suppl., 120, 153-156, (1997) (2) 'Spectral and Temporal Variability in the X-ray Flux'. of GSll24-683, Nova Muscae 1991", M. Takizawa, T. Dotani, K. Mitsuda, E. Matsuba, M. O;;awa, T. Aoki, K. Asai, K. Ebisawa, K. Makishima, S. Miyamoto, S . Iga, B. Vaughan, R. Rc.tledge, & W. Lewin, Astrophys, J., 489, 272, (1997).

Source record↗
NASA NTRS2004

Investigations into Gravitational Wave Emission from Compact Body Inspiral Into Massive Black Holes

Much of the grant's support (and associated time) was used in developmental activity, building infrastructure for the core of the work that the grant supports. Though infrastructure development was the bulk of the activity supported this year, important progress was made in research as well. The two most important "infrastructure" items were in computing hardware and personnel. Research activities were primarily focused on improving and extending. Hughes' Teukolsky-equation-based gravitational-wave generator. Several improvements have been incorporated into this generator.

Hughes, Scott A.↗
NASA NTRS1999

Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei

Emission-line variability data on NGC 5548 argue strongly for the existence of a mass of order 7 x l0(exp 7) solar mass, within the inner few light-days of the nucleus in the Seyfert 1 galaxy NGC 5548. The time-delayed response of the emission lines to continuum variations is used to infer the size of the line-emitting region, and these determinations are combined with measurements of the Doppler widths of the variable line components to estimate a virial mass. The data for several different emission lines spanning an order of magnitude in distance from the central source show the expected V proportional to r(sup -1/2) correlation and are consistent with a single value for the mass.

Peterson, Bradley M.↗
NASA NTRS2004

AGN Black Hole Masses from Reverberation Mapping

Emission-line variability data on bright AGNs indicates that the central objects in these sources have masses in the million to few-hundred million solar mass range. The time-delayed response of the emission lines to continuum variations can be used to infer the size of the line-emitting region via light travel-time arguments. By combining these sizes with the Doppler widths of the variable part of the emission lines, a virial mass estimate can be obtained. For three especially well-studied sources, NGC 5548, NGC 7469, and 3C 390.3, data on multiple emission lines can be used to test the virial hypothesis. In each of these cases, the response time of the various emission lines is anticorrelated with the line width, with the dependence as expected for gravitationally bound motion of the line-emitting clouds, i.e., that the square of the Doppler line width is inversely proportional to the emission-line time delay. Virial masses based on the Balmer lines have now been measured for about three dozen AGNs. Systematic effects currently limit the accuracy of these masses to a factor of several, but characteristics of the radius-luminosity and mass-luminosity relationships for AGNs are beginning to emerge.

Peterson, B. M.↗
NASA NTRS2000

Three-Layered Atmospheric Structure in Accretion Disks Around Stellar-Mass Black Holes

Modeling of the x-ray spectra of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40 reveals a three-layered atmospheric structure in the inner region of the inner accretion disks. Above the cold and optically thick disk with a temperature of 0.2 to 0.5 kiloelectron volts, there is a warm layer with a temperature of 1.0 to 1.5 kiloelectron volts and an optical depth around 10. Sometimes there is also a much hotter, optically thin corona above the warm layer, with a temperature of 100 kiloelectron volts or higher and an optical depth around unity. The structural similarity between the accretion disks and the solar atmosphere suggests that similar physical processes may be operating in these different systems.

Zhang, S. N.↗
NASA NTRS1999

Discovery of a Three-Layered Atmospheric Structure in Accretion Disks around Stellar-Mass Black Holes

We have carried out systematic modeling of the X-ray spectra of the Galactic superluminal jet sources GRS 1915+105 and GRO J1655-40, using our newly developed spectral fitting methods. Our results reveal, for the first time, a three-layered structure of the atmosphere in the inner region of the accretion disks. Above the conanonly known, cold and optically thick disk of a blackbody temperature 0.2-0.5 keV, there is a layer of warm gas with a temperature of 1.0-1.5 keV and an optical depth of around 10. Compton scattering of the underlying disk blackbody photons produces the soft X-ray component we comonly observe. Under certain conditions, there is also a much hotter, optically thin corona above the warm layer, characterized by a temperature of 100 keV or higher and an optical depth of unity or less. The corona produces the hard X-ray component typically seen in these sources. We emphasize that the existence of the warm layer seem to be independent of the presence of the hot corona and, therefore, it is not due to irradiation of the disk by hard X-rays from the corona. Our results suggest a striking structural similarity between the accretion disks and the solar atmosphere, which may provide a new stimulus to study the common underlying physical processes operating in these vastly different systems. We also report the first unambiguous detection of an emission line around 6.4 keV in GRO J1655-40, which may allow further constraining of the accretion disk structure. We acknowledge NASA GSFC and MFC for partial financial support. (copyright) 1999: American Astronomical Society. All rights reverved.

Zhang, S. N.↗
NASA NTRS2005

Investigations into Gravitational Wave Emission from Compact Body Inspiral into Massive Black Holes

In contrast to year 1 (when much of the activity associated with this grant focused upon developing our group at MIT), year 2 was a period of very focused attention on research problems. We made significant progress developing relativistic waveforms for the extreme mass ratio inspiral problem; we have pushed forward a formalism our group developed for mapping the spacetimes of massive compact objects; and, in collaboration with the Caltech group, we began to develop a framework for addressing issues in LISA data analysis for extreme mass ratio systems.

Hughes, Scott A.↗
NASA NTRS2005

An Integral Study of Galactic Black Hole States

XTE 51550-564 was clearly detected with INTEGRAL out to 600 keV with the SPI, and is one of only two sources detected with IBISPICSIT. Software difficulties in analyzing the data prevented us from progressing with the analysis past the most elementary stages (see last year's report). The support from the INTEGRAL help desk has been very disappointing. People affiliated with INTEGRAL published a paper on the results of our data before we could master the reduction and analysis software. We are not the only group that got stuck with the analysis without adequate support from the INTEGRAL help desk. This was a rather disappointing experience as we lost many months of valuable time and efforts.

Source record↗
NASA NTRS2006

The Swift Gamma-ray Burst Explorer: Early views into Black-hole Creation

Swift has exceeded every pre-launch predicted advance in GRB science. It has discovered the farthest GRB ever seen and identified new GRBs at a rate of 100/year. It has also explored a brand new time interval in GRB light curves by revealing unpredicted phenomena of GRB flares and rapid x-ray afterglow declines. Swift has conducted 20,00o successful slews to sources and is predicted to stay in orbit until 2022.

Hill, Joe↗