Engineering topics

Boldt, Elihu

Publications and source records attributed to Boldt, Elihu.

18 records

NASA NTRS2000

Cosmic Ray and Tev Gamma Ray Generation by Quasar Remnants

Results from new broadband (radio to X-ray) high-resolution imaging studies of the dormant quasar remnant cores of nearby giant elliptical galaxies are now shown to permit the harboring of compact dynamos capable of generating the highest energy cosmic ray particles and associated curvature radiation of TeV photons. Confirmation would imply a global inflow of interstellar gas all the way to the accretion powered supermassive black hole at the center of the host galaxy.

Boldt, Elihu↗

NASA NTRS1994

The cosmic X-ray background-IRAS galaxy correlation and the local X-ray volume emissivity

We have cross-correlated the galaxies from the IRAS 2 Jy redshift survey sample and the 0.7 Jy projected sample with the all-sky cosmic X-ray background (CXB) map obtained from the High Energy Astronomy Observatory (HEAO) 1 A-2 experiment. We have detected a significant correlation signal between surface density of IRAS galaxies and the X-ray background intensity, with W(sub xg) = (mean value of ((delta I)(delta N)))/(mean value of I)(mean value of N)) of several times 10(exp -3). While this correlation signal has a significant implication for the contribution of the local universe to the hard (E greater than 2 keV) X-ray background, its interpretation is model-dependent. We have developed a formulation to model the cross-correlation between CXB surface brightness and galaxy counts. This includes the effects of source clustering and the X-ray-far-infrared luminosity correlation. Using an X-ray flux-limited sample of active galactic nuclei (AGNs), which has IRAS 60 micrometer measurements, we have estimated the contribution of the AGN component to the observed CXB-IRAS galaxy count correlations in order to see whether there is an excess component, i.e., contribution from low X-ray luminosity sources. We have applied both the analytical approach and Monte Carlo simulations for the estimations. Our estimate of the local X-ray volume emissivity in the 2-10 keV band is rho(sub x) approximately = (4.3 +/- 1.2) x 10(exp 38) h(sub 50) ergs/s/cu Mpc, consistent with the value expected from the luminosity function of AGNs alone. This sets a limit to the local volume emissivity from lower luminosity sources (e.g., star-forming galaxies, low-ionization nuclear emission-line regions (LINERs)) to rho(sub x) less than or approximately = 2 x 10(exp 38) h(sub 50) ergs/s/cu Mpc.

Miyaji, Takamitsu↗

NASA NTRS1993

A Broad-Band X-Ray Telescope spectrum of the massive X-ray binary X Persei

The Broad Band X-Ray Telescope, covering the 0.3-12 keV bandpass with moderate spectral resolution, observed the Be/X-ray binary X Per in 1990 December during the Astro-l mission on the Space Shuttle Columbia. The data obtained are the best to date to search for lines and edges. The data are well fitted by a power-law spectrum with a high-energy cutoff. A low value for the high-energy cutoff is found, implying a slightly weaker magnetic field strength for the X-ray pulsar. No iron line is present at about 6.5 keV with an equivalent width greater than 30-40 eV. The BBXRT observation corresponded to the 'off' state of X Per's recent 'phase change'.

Schlegel, Eric M.↗

NASA NTRS1993

On Compton reflection in the sources of the cosmic X-ray background

Consideration is given to recent models for the cosmic X-ray background that assume that it originates from unresolved AGN emitting spectra due to enhanced Compton reflection of a power-law photon spectrum incident on cold matter. The parameter space of the Compton reflection model is studied, and the allowed parameter space is found to be severely constrained by physical and cosmological effects. For an incident power-law energy index alpha is greater than about 1, the X-ray peak in the observed spectrum from a population of AGN is necessarily at an energy less than that of the observed peak. Two examples of improved fits to the X-ray background are shown. It is concluded that the Compton reflection models proposed to date do not provide a straightforward explanation of the X-ray background spectrum.

Zdziarski, Andrzej A.↗

NASA NTRS1992

Spectral-luminosity evolution of active galactic nuclei and the cosmic X- and gamma ray background

Coherent electromagnetic dynamo acceleration processes, which act on charge particles within the context of black hole accretion disk scenarios, are generally regarded as the underlying central power source for active galactic nuclei (AGN). If the precursor active galaxies (PAG) for such AGN are formed at high redshift and contain initial seed black holes with mass approximately equal to 10(exp 4) solar masses, then the Eddington limited X-ray radiation emitted during their lifetime will undergo the phenomenon of 'spectral-luminosity evolution'. When accretion disks are first formed at the onset of galaxy formation the accretion rate occurs at very high values of luminosity/size compactness parameter L/R greater than 10(exp 30) erg/cm-sec. In the absence of extended structure, such high values of L/R generate dynamic constraints which suppress coherent, black hole/accretion disk dynamo particle acceleration processes. This inhibits nonthermal radiation processes and causes the spectrum of X-radiation emitted by PAG to be predominantly thermal. A superposition of PAG sources at z is greater than or equal to 6 can account for the residual cosmic X-ray background (CXB) obtained from the total CXB after subtraction of foreground AGN sources associated with present epoch Seyfert galaxies. The manner in which the PAG undergo spectral-luminosity evolution into Seyfert galaxies is investigated.

Leiter, Darryl↗

NASA NTRS1992

Spectral-luminosity evolution of active galactic nuclei (AGN)

The origin of the cosmic X-ray and gamma-ray backgrounds is explained via the mechanism of AGN spectral-luminosity evolution. The spectral evolution of precursor active galaxies into AGN, and Newton-Raphson input and output parameters are discussed.

Leiter, Darryl↗

NASA NTRS1991

Cross-correlation of the X-ray background with nearby galaxies

The detection of a signal in the cross-correlation of the diffuse 2-10 keV HEAO 1 A-2 X-ray surface brightness with the galaxy surface density derived from diameter-limited samples from the Uppsala General Catalogue is reported. An ad hoc relationship between the X-ray flux and the galaxy counts is used to estimate the local X-ray volume emissivity at 2.8 + or - 1.0 x 10 to the 38th ergs/s/cu Mpc. This result implies that unevolved populations of X-ray sources correlated with present-epoch galaxies can contribute only 13 + or - 5 percent of the cosmic X-ray background.

Jahoda, Keith↗

NASA NTRS1991

Spectral-luminosity evolution of active galactic nuclei and the cosmic X-ray background

Black hole accretion disk dynamo processes are generally regarded as the central power source for AGN (Rees, 1984). If the precursor active galaxies for such AGN are formed at redshift z greater than about 4 and contain initial central seed black holes about 10 exp 6 solar masses, then the Eddington limited X-ray radiation emitted during their lifetime will undergo the phenomenon of 'spectral-luminosity evolution'. When accretion disks are first formed at the onset of galaxy formation, the accretion rate occurs at high values of luminosity/size compactness parameter L/R greater than 10 exp 30 erg/cm-sec. Such high values of L/R generate dynamic constraints which suppress nonthermal black hole accretion disk dynamo processes in favor of thermal processes. This causes the spectrum of X-radiation emitted by early AGN to be predominantly thermal. A superposition of such thermal, comptonized PAG sources can account for the residual cosmic X-ray background and can act as a source of X-ray heating of the intergalactic medium for z greater than about 4.

Leiter, Darryl↗

NASA NTRS1991

The X-ray flux dipole of AGNs as an indicator of the local gravitational field

We have investigated the dipole anisotropy of the sky X-ray flux from nearby AGNs to compare with the peculiar motion of the Local Group (LG) using a more extensive sample than that of Miyaji and Boldt (1990). We have sampled 56 low redshift emission-line AGNs (z less than 0.06) from the HEAO 1 A-2 experiment with a flux limit lower than that of Piccinotti et al. (1982) and with a lower galactic latitude cutoff. Our sample shows a significant dipole anisotropy whose apex is only about 30 deg away from the direction of the Local Group's peculiar motion for the objects with z less than 0.015. The dipole growth vs. redshift shows a sharp rise between z = 0.006 and z = 0.015; the amplitude of the dipole is 40 +/- 10 percent of the corresponding monopole at z = 0.015. The outer redshift cutoff is consistent with the results obtained from analyses using optical and IRAS galaxies. The present sample strengthens our previous conclusion that X-ray emission from AGNs traces the underlying mass distribution as strongly as optical and IR emission from galaxies.

Miyaji, Takamitsu↗

NASA NTRS1990

Spectral evolution of active galactic nuclei Penrose Compton scattering processes and gamma ray emission from Seyfert galaxies

In black hole spectral evolution models for active galactic nuclei (AGN), present epoch Seyfert galaxies evolve from an earlier precursor active galaxy (PAG) stage at redshift z is approximately 7 where they acted as the thermal sources responsible for the residual cosmic x ray background (RCXB). The Seyfert galaxies which emerge in this context emit Penrose Compton Scattering (PCS) gamma ray transients on the order of hours with a kinematic cutoff in the spectrum less than or equal to 3 MeV. The EGRET (Energetic Gamma-Ray Experimental Telescope/ OSSE (Oriented Scintillation Spectrometer Experiment/ COMPTEL (Compton Telescope)/ BATSE (Burst and Transient Source Experiment) instruments on the Gamma Ray Observatory (GRO) are appropriate instruments to carry out further tests of this model by studying: PCS gamma ray transient emission from individual galaxies and, the possibility that present epoch PCS gamma ray emitting Seyfert galaxies contribute observable temporal variability to the excess diffuse gamma ray background component less than or equal to 3 MeV.

Leiter, Darryl↗

NASA NTRS1990

The X-ray flux dipole of active galactic nuclei and the peculiar motion of the Local Group

X-ray emission from 30 resolved AGN's are used to study the dipole moment of their flux distribution on the sky. The data are derived from the Piccinotti et al. (1982) survey. X-ray fluxes are analyzed in terms of the alignment with the direction of the Local Group (LG) of galaxies. It is observed that the direction of the dipole moment of the flux is (313 deg, 38 deg); the dipole direction deviates from the LG velocity by 39 deg. It is detected that the amplitude of the dipole is about 50 percent of the corresponding monopole. Based on a comparison of the data with previous observations it is suggested that the X-ray emission from AGNs traces the underlying mass distribution at least as strongly as optical and IR emission from galaxies.

Miyaji, Takamitsu↗

NASA NTRS1990

The all-sky X-ray foreground - Outstanding issues

An all-sky X-ray foreground survey can be used to determine how supermassive black holes trace the underlying mass distribution responsible for the particular velocity of the local group. The dipole moment for the cosmic X-ray background is compared to that for the all-sky extragalactic foreground of discrete sources, and the survey of AGNs is determined to be an effective method for discerning pronounced large-scale foreground anisotropies. The required sensitivity for an all-sky survey of this type is found to be 3.3 x 10 to the -13th ergs/sq cm/s which would allow an unbiased AGN survey.

Boldt, Elihu↗

NASA NTRS1990

The all-sky extragalactic X-ray foreground

It is argued that the local gravitational dipole implied by the 50 brightest X-ray clusters of galaxies at z greater than 0.013 considered by Lahav et al. (1989) is relatively small compared with that inferred from the only three clusters at lower redshifts. Recent dipole analysis of the X-ray flux from bright AGN observed with HEAO-1A2 indicates that they are indeed strong tracers of this matter. The implications of this for the very pronounced large-scale foreground anisotropies to be measured via low-redshift AGN resolved in more sensitive all-sky surveys are explored. For the total extragalactic X-ray sky, i.e., including the relatively large Cosmic X-ray Background as well as the contribution of the resolved sources, the dipole moment is small compared to the monopole. Because of the large peculiar velocity of the Local Group, it is found that the currently estimated value for this total dipole moment can be used to set severe constraints on the volume emissivity arising from all X-ray sources within the present epoch.

Boldt, Elihu↗

NASA NTRS1989

Is AGN spectral evolution needed for the CXB

The principal sources of the cosmic X-ray background (CXB) can be objects indicative of a physically early stage of active galactic nuclei (AGN) evolution. Such an evolutionary scenario is examined by using the HEAO-1 A2 X-ray selected sample of bright AGN as a diagnostic of anisotropies in the unresolved background. The observed limit on CXB global anisotropy is used to place an upper bound on the present-epoch volume emissivity of unresolved X-ray sources. Considering the A2 AGN count, CXB surface brightness fluctuations observed at higher energies (via HEAO-1 A4) suggest that present-epoch AGN could have the broadband spectral structure needed for the redshifted contributions of more luminous AGN with this same spectrum to account for the entire CXB.

Boldt, Elihu↗

NASA NTRS1989

The X-ray log N-log S relation

Results from various surveys are reviewed as regards X-ray source counts at high galactic latitudes and the luminosity functions determined for extragalactic sources. Constraints on the associated log N-log S relation provided by the extragalactic X-ray background are emphasized in terms of its spatial fluctuations and spectrum as well as absolute flux level. The large number of sources required for this background suggests that there is not a sharp boundary in the redshift distribution of visible matter.

Boldt, Elihu↗

NASA NTRS1988

A bound on X-ray emission from the intrasupercluster medium

The Bahcall-Soneira (1984) complete sample of superclusters was searched for X-ray emission in the HEAO 1 A-2 data base. No statistically significant emission from diffuse intrasupercluster gas was detected; a 3-sigma upper limit to the mean individual flux is 10 to the -11th ergs/sq cm per s. Implications of this bound to measurements of the Zeldovich-Sunyaev (1969) effect toward clusters within a supercluster and to the supercluster contribution to the cosmic X-ray background are discussed.

Persic, Massimo↗

NASA NTRS1987

Constraints on possible precursor AGN sources of the cosmic X-ray background

New limits on small-scale surface brightness fluctuations of the residual cosmic X-ray background are used to reevaluate the conjecture that unresolved precursor AGN sources could be the origin of the flux. The large number of these predominantly X-ray-emitting objects thereby required imposes that their lifetime be longer than previously considered. Attention is drawn to the fact that the reduction in the effective Eddington luminosity limit for such sources due to electron-positron pair opacity could have the effect of increasing their lifetime to an appropriate level.

Boldt, Elihu↗

NASA NTRS1987

The cosmic X-ray background

As the sky in the microwave band is dominated by a cosmic background, so too is the X-ray sky. In this presentation the observational situation regarding the extragalactic X-ray background is reviewed, emphasizing data obtained from HEAO-1 and the Einstein Observatory (HEAO-2). Spectral characteristics and spatial variations are described and discussed within the context of what is currently known about individual extragalactic sources. It is concluded that the bulk of the cosmic X-ray background is yet to be understood. Possibilities range from genuinely diffuse emission to an 'as yet' unknown large population of unresolved discrete sources. The role of cosmological effects is examined and could be important.

Boldt, Elihu↗