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At least 1,153 records · Page 64
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

The search for, and study of black holes in the galaxy

The study of the short-term (less than 10 s) time variability of Cygnus X-1 is reviewed, with attention given to measurements of the autocorrelation function and of the cross-correlation between different energy bandwidths, as well as to a simple shot noise model for describing all such short-term variations. Observational questions with regard to Cygnus X-1 are discussed, relating to the average shape of the randomly occurring flares, energy dependence in the cross-correlation and the dependence on energy of the X-ray polarization. Concerning the study of the Cyg X-1-like aperiodic X-ray sources, an estimate is made of what can be accomplished at the limits of sensitivity where Poisson fluctuations are at least as important as the intrinsic variability of the source, considering the third moment due to the source fluctuations.

Weisskopf, M. C.↗
NASA NTRS1985

Breakdown of helium nuclei in matter processed near black holes

The rate of breakup of helium nuclei by particle induced reactions is computed. It is shown that the rate is determined by the endothermic reaction p + 4He 3He + d, becoming effective at kT approx. few MeV. It is suggested that matter having been processed to these temperatures will be depleted in helium and in the elements C, N, O, and Ne.

Gould, R. J.↗
NASA NTRS1988

The potential role of gamma-ray observations in the study of massive black holes

Existing gamma-ray data on active galaxies are summarized. It is shown that diffuse extragalactic gamma radiation may be the result of active galaxies extended over cosmological distances. The principal satellite opportunities for active galaxy gamma-ray astronomy in the near future are Gamma-I, Sigma, and the Gamma Ray Observatory; the latter will permit highly sensitive measurements of gamma-ray specra from below 0.1 MeV to above 10,000 MeV.

Fichtel, Carl E.↗
NASA NTRS1989

Ideal black hole gas

The concept of a primordial blackhole fluid with intrinsic spin density is examined along with its consequence for supercluster-sized, i.e., large scale voids, and the missing mass question.

Smalley, Larry L.↗
NASA NTRS1990

Quasinormal modes of Reissner-Nordstrom black holes

A matrix-eigenvalue algorithm is presented for accurately computing the quasi-normal frequencies and modes of charged static blackholes. The method is then refined through the introduction of a continued-fraction step. The approach should generalize to a variety of nonseparable wave equations, including the Kerr-Newman case of charged rotating blackholes.

Leaver, Edward W.↗
NASA NTRS1991

A search for periodicity in the x ray spectrum of black hole candidate A0620-00

The archived data from the SAS-3 observations of the X-ray nova A0620-00, the best of the stellar blackhole candidates, were exhaustively examined for evidence of variable phenomena correlated with the orbital motion of the binary system of which it is a member. The original analysis of these data was completed before discovery of the binary companion and determination of the orbital period of the system. New interest was drawn to the task of a reexamination of the archive data by the recent discovery of the massive nature of the X-ray source through analysis of the Doppler variations and ellipsoidal light variations of the faint K-star companion by McClintock and Remillard. The archive research, carried out under the supervision of the principal investigator, was the topic of the thesis submitted to the MIT Department of Physics by Kenneth Plaks in partial fulfillment of the requirements for the degree of Master of Science. Plaks' effort was focused on the elimination of fluctuations in the data due to errors in attitude solutions and other extraneous causes. The first products of his work were long-term light curves of the X-ray intensities in the various energy channels as functions of time during the time from outbursts in August 1975 to quiescence approximately 6 months later. These curves, are refined versions of the preliminary results published in 1976 (Matilsky et al. 1976). Smooth exponentials were fitted to these long term light curves to provide the basis for detrending the data, thereby permitting a calculation of residuals derived by subtracting the fitted curve from the data. The residuals were then analyzed by Fourier analysis to search for variations with the period of the binary orbit, namely 7.75 hours. No evidence of an orbital periodicity was found. However, the refined light curve provides a much clearer picture of the outburst and subsequent decay of the X-ray luminosity. In fact, there were two outbursts, each followed by an exponential decay with similar time constants of about 25 days. Previous evidence of a three-oscillation variation with a 7.8 day period were confirmed. Substantial theoretical effort has been devoted to attempts to account for the decay characteristics as the result of the gradual eating up of an accretion disk by a stellar-mass blackhole (e.g., Huang and Wheeler 1989). The improved decay curves will provide significant new constraints on the theoretical analyses.

Clark, George W.↗
NASA NTRS1994

Black hole accretion disks with coronae

Observations suggest the existence of both hot and cold dark matter in the centers of active galactic nuclei. Recent spectral models require a major fraction of power to be dissipated in the hot matter. We study the case when the hot matter forms a corona around a standard cold alpha-disk. In particular, we investigate the case when a major fraction, f, of the power released when the cold matter accretes is transported to and dissipated in the corona. This has major effects on the cold disk, making it colder, more geometrically thin, denser, and having larger optical depths. One important consequence is the disappearance of the effectively optically thin zone as well as of the radiation pressure dominated zone for values of f sufficiently closed to unity. The disappearance of the radiation pressure dominated zone will result in a cold disk with only a gas pressure dominated zone that is stable against thermal and viscous instabilities. We also show that the pressure ( and the radiation) from the corona will only affect the surface layers of the cold disk. Our results disagree with those of other recent work on accretion disks with coronae. We find those works to be based on unphysical assumptions.

Svensson, Roland↗
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.↗