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Leiter, D.

Publications and source records attributed to Leiter, D..

18 records
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NASA NTRS1988

Spectral evolution in black hole accretion powered AGN and the cosmic X-ray background

If AGN contain supermassive black holes of pregalactic origin, then the radiation emitted during their lifetime will undergo spectral evolution. For AGN black-hole-accretion disk dynamo power sources, the dynamic parameters relevant to spectral evolution are the electron crossing time in the dynamo, the electron radiative loss time, the compactness parameter, and the photon-photon pair production optical depth. It is suggested that both spectral and luminosity evolution may be required to explain the evolutionary properties of AGN.

Leiter, D.↗
NASA NTRS1986

Spectral evolution in young active galactic nuclei

The spectral evolution of AGNs is discussed within the context of a scenario where the cosmic X-ray background (CXB) is dominated by these sources. Attention is draqwn to the fact that the individually observed AGN X-ray spectra are significantly steeper than that of the CXB. The remarkably flat spectrum thereby required for the 'as-yet' unresolved sources of the residual CXB is interpreted as an observational constraint on an earlier stage of AGN evolution. Assuming black hole disk accretion, a picture emerges where young AGNs are compact Eddington limited thermal X-ray sources and where canonical AGNs represent later stages in which they have become appreciably less compact, exhibiting the importance of nonthermal disk-dynamo processes.

Boldt, E.↗
NASA NTRS1985

Can the master time asymmetry in nature be electrodynamic in origin?

If the electrodynamic measurement process is operationally described by imposing measurement color onto classical electrodynamics, self-energy infinities are eliminated and a retarded electrodynamic time arrow emerges dynamically from internal dynamic-stability conditions. This occurs because the new formalism contains nonlocal radiation fields which carry a negative parity under mathematical time reversal. This result is shown to be compatible with an extended form of T and CPT symmetry which preserves the dynamically chosen retarded electrodynamic arrow of time in the measurement color electrodynamic formalism.

Leiter, D.↗
NASA NTRS1984

Optical characteristics of young quasars as sources of the cosmic X-ray background

The sources which dominate the thermal cosmic X-ray background cannot have X-ray spectra similar to the power laws measured for bright active galactic nuclei. The optical consequences of this disparity are pursued by considering a standard model for the photoexcitation and heating of the line-emitting gas surrounding a central source (e.g., such as a quasar). The optical line emission to be associated with compact young quasar sources having the same X-ray spectrum as the X-ray background is found to be substantially different from that characteristic of typical quasars. Implications on quasar source counts and the identification of such new objects are discussed.

Boldt, E.↗
NASA NTRS1983

Optical characteristics of young quasars as sources of the cosmic X-ray background

The sources which dominate the thermal cosmic X-ray background cannot have X-ray spectra similar to the power laws measured for bright active galactic nuclei. The optical consequences of this disparity are pursued by considering a standard model for the photoexcitation and heating of the line emitting gas surrounding a central source (e.g., such as a quasar). The optical line emission to be associated with compact young quasar sources having the same X-ray spectrum as the X-ray background is found to be substantially different from that characteristic of typical quasars. Implications on quasar source counts and the identification of such new objects are discussed.

Boldt, E.↗
NASA NTRS1982

Spectral evolution of active galactic nuclei: A unified description of the X-ray and gamma

A model for spectral evolution is presented whereby active galactic nuclei (AGN) of the type observed individually emerge from an earlier stage at z approx = 4 in which they are the thermal X-ray sources responsible for most of the cosmic X-ray background (CXB). The conjecture is pursued that these precursor objects are initially supermassive Schwarzschild black holes with accretion disks radiating near the Eddington luminosity limit. It is noted that after approx. 10 to the 8th power years these central black holes are spun-up to a canonical Kerr equilibrium state (A/M = 0.998; Thorne 1974) and shown how they then can lead to spectral evolution involving non-thermal emission extending to gamma rays, at the expense of reduced thermal disk radiation. That major portion of the CXB remaining after the contribution of usual AGN are considered, while a superposition of AGN sources at z 1 can account for the gamma ray background. Extensive X-ray measurements carried out with the HEAO 1 and 2 missions as well as gamma ray and optical data are shown to compare favorably with principal features of this model.

Leiter, D.↗
NASA NTRS1981

Precursor active galaxies and the cosmic X-ray background

Consideration is given to Carr's theory (1980) that most cosmic X-ray background is produced by thermal X-ray emission associated with black hole accretion disks for compact objects. It is posited that the onset of significant X-rays occurs during galaxy formation when accretion disks are formed by the interaction of young galaxies and massive black holes of pregalactic origin. The study suggests that most cosmic X-ray background could be produced from distant sources with a low ratio of optical to X-ray luminosity. Precursor active galaxy objects involving a massive black hole surrounded by a hot optically thin accretion disk radiating near the Eddington luminosity limit and with an effective temperature of about 2 x 10 to the 9th K would fulfill the condition and produce the correct background spectrum and intensity. This model also associates cosmic X-ray background and nonthermal gamma-ray background to active galaxies, thus implying that massive black holes are associated with their internal dynamics.

Boldt, E.↗
NASA NTRS1981

Gamma ray lines from the Galactic Center and gamma ray transients

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.↗
NASA NTRS1981

Precursor active galaxies and the cosmic X-ray background

It is argued that the cosmic X-ray background (CXB) is not dominated by sources that are usual active galaxies or quasars. A comparable number of objects, young galaxies at z approximately 4 containing massive black holes surrounded by hot optically thin accretion disks, constitute the precursor active galaxies (PAG) postulated here for producing the thermal type spectrum required for the CXB. An evolutionary track for such PAG objects is described which would lead to the active galaxies observed as individual nonthermal sources. Unresolved emission from active galaxies at z 1 could then readily account for most of the nonthermal background observed in the gamma ray band.

Boldt, E. A.↗
NASA NTRS1981

Origin of 0.511 MeV emission from the Galactic center

The observations of 0.511 MeV positron annihilation radiation from the direction of the Galactic center are reviewed, and the implications of the line intensity, the shape of the line, and the position and angular size of the line emission region are discussed. These observations appear to require a compact source at the Galactic center, and within the constraints of both the 0.511 MeV observations and the hard X-ray, infrared and radio observations, a model is proposed of positron production and annihilation around a massive black hole in the Galactic nucleus.

Lingenfelter, R. E.↗
NASA NTRS1981

Precursor active galaxies, active galaxies and the X-ray and gamma-ray background

A description is presented of a model in which the X-ray and gamma-ray background can result from the superposition of radiation from active galaxies in different stages of their evolutionary history. This scheme is based on the generalization of a black-hole model developed for gamma-ray production in active galaxies by Leiter (1980). Both thermal and nonthermal accretion disk processes around massive rotating Kerr black holes are considered. Attention is given to cosmological conditions leading to precursor active galaxies (PAG), PAG as origin of the cosmic X-ray background, and the evolution of PAG into Seyfert galaxies as origin of the gamma-ray background. It is found that after spin-up of the central black hole an active galactic nucleus can generate nonthermal radiation very efficiently up to a few MeV.

Leiter, D.↗
NASA NTRS1980

The Penrose Photoproduction Scenario for NGC 4151 /PCS-SSC/ - A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies

On the basis of general arguments, it has been suggested (Bignami et al., 1979) that a steepening of the spectrum between X-ray and gamma-ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma-ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. It is shown that the above suggestion can be given a consistent theoretical interpretation in the context of the Penrose Photoproduction Scenario (PCS-SSC). Specifically in the case of NGC 4151, the dominant process will be shown to be Penrose Compton Scattering PCS in the ergosphere of a massive, central, rapidly spinning Kerr black hole, assumed in its nucleus. It is assumed that PCS gamma-ray induced electron-position, Synchrotron-Self-Compton processes 'evolve' as the dominant source of nonthermal X-rays.

Leiter, D.↗
NASA NTRS1979

The Penrose photoproduction scenario for NGC 4151: A black hole gamma-ray emission mechanism for active galactic nuclei and Seyfert galaxies

A consistent theoretical interpretation is given for the suggestion that a steepening of the spectrum between X-ray and gamma ray energies may be a general, gamma-ray characteristic of Seyfert galaxies, if the diffuse gamma ray spectrum is considered to be a superposition of unresolved contributions, from one or more classes of extragalactic objects. In the case of NGC 4151, the dominant process is shown to be Penrose Compton scattering in the ergosphere of a Kerr black hole, assumed to exist in the Seyfert's active galactic nucleus.

Leiter, D.↗
NASA NTRS1979

Penrose pair production as a power source of quasars and active galactic nuclei

Penrose pair production in massive canonical Kerr black holes (those with a/M equal to 0.998) is proposed as a way to explain the nature of the vast fluctuating energy production associated with active galactic nuclei and quasars. It is assumed that a Kerr black hole with a mass of the order of 100 million solar masses lies at the center of an active nucleus and that an accretion disk is formed. Penrose pair production in the inner ergosphere of such a massive canonical Kerr black hole is analyzed. The results indicate that: (1) particle pairs are ejected within a 40 deg angle relative to the equator; (2) the particle energy is of the order of 1 GeV per pair; (3) the pressure of the electron-positron relativistic gas is proportional to the electron-positron number density; (4) pair production may occur in bursts; and (5) the overall lifetime of an active nucleus would depend on the time required to exhaust the disk of its matter content. A test of the theory is suggested which involves observation of the 0.5-MeV pair-annihilation gamma rays that would be generated by annihilating particle pairs.

Kafatos, M.↗
NASA NTRS1979

Penrose photoproduction processes - A high efficiency energy mechanism for active galactic nuclei and quasars

Recent observations of NGC 4151 and 3C273 suggest that the nuclei of active galaxies have very high gamma ray efficiencies. In addition, optical studies of M87 have indicated the possibility of a massive black hole in its central region. The above facts have led to study of a new physical mechanism, Penrose Photoproduction Processes, in the ergospheres of massive Kerr black holes, as a way to account for the fluctuating, high efficiency, energy production associated with active galaxies and quasars. Observational signatures, associated with this mechanism, occur in the form of approximately 2 MeV and approximately 2 GeV gamma ray cutoffs which might be corroborated by the observed spectra of NGC 4151 and 3C273, respectively.

Leiter, D.↗