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At least 649 records · Page 36
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NASA NTRS1980

Gamma rays from Penrose powered black holes in Centaurus A, 3C 273, and NGC 4151

Gamma-ray observations of Cen A, 3C 273, and NGC 4151 are examined under the assumption that Penrose collision processes in the ergospheres of massive black holes power their nuclei. The observed sharp break in the MeV region of the NGC spectrum is attributed to Penrose Compton scattering, and the absence of an MeV break in the spectra of Cen A and 3C 273 implies Penrose pair production. Central black hole masses of tens of millions of solar masses for NGC 4151 and Cen A, and tens of billions of solar masses for 3C 273, are obtained. Attention is also given to accretion rate, the efficiency of accretion, QSOs and Seyferts.

Kafatos, M.↗
NASA NTRS1980

The nebulosity associated with 3C 120

Spectrophotometric observations have been made of the nebulosity surrounding the Seyfert (or N) galaxy 3C 120, as well as of the nucleus. Observations of the nebulosity reveal an extensive network of H II regions characterized by a high ionization level, which, it is argued, is due to photoionizations by the nucleus. The O/H and N/O abundance ratios in this gas, at least as far out as 8 kpc from the nucleus, must be within a factor of 20 of the solar values. The velocity field of this gas is very chaotic, but the systematic gas velocities, relative to the nucleus, are mostly positive to one side of an axis passing through the nucleus at P.A. 72 deg and mostly negative on the other side. The position angle of this axis is consistent with the direction (P.A. 65 deg) along which the compact radio source in the nucleus is expanding, but it is about 45 deg away from the major or minor axes of the fainter elliptical structure visible on previously published broad-band direct plates.

Baldwin, J. A.↗
NASA NTRS1980

Radio survey of Markarian galaxies at 6 and 11 cm

One hundred and fifty-one objects from Markarian's lists 6 and 7 were observed at 6 cm with a 3 sigma detection limit of about 30 mJy. Eight Markarian objects were detected, six of which were also observed at 11 cm. Forty-five others were negative at this wavelength. Two of the detections, numbers 533 and 668, are Seyfert galaxies; additionally, UB1 was detected at 6 cm and NGC 7715 and III Zw 2 were found at 11 cm.

Kojoian, G.↗
NASA NTRS1980

X-ray spectral constraints on the broad-line cloud geometry of NGC 4151

X-ray spectral data from NGC 4151 taken with the Einstein Solid-State Spectrometer (SSS) and the HEAO 1 A-2 experiment cannot be simply reconciled with absorption from a uniform column of cold gas. The SSS data can, however, be explained in terms of a clumped absorber with approximately 10% uncovered fraction and factor-of-two overabundances in Z equal to or greater than 14 elements relative to solar oxygen. It is shown that these and previously reported spectral and variability data can be quantitatively reconciled with absorption arising in the cold clouds responsible for the broad optical line emission if the cloud dimensions are small compared to the central source size. It is suggested that the lack of significant X-ray absorption observed from much higher luminosity Seyferts and quasars is a natural consequence of the proposed picture for NGC 4151.

Holt, S. S.↗
NASA NTRS1980

Extended 20 micron emission from the center of NGC 1068

Multiaperture photometry of the Seyfert galaxy NGC 1068 is reported which demonstrates that significant 20 micron emission originates at positions located more than 3 arcsec, or 260 pc, from the nucleus. These observations strongly support arguments that most of the infrared flux is thermal emission from dust. It is argued that the dust giving rise to this extended emission cannot be heated solely by a compact nuclear object. It is suggested that there is a powerful energy-generation mechanism, possibly an enormous burst of star formation, operating on a scale much larger than that identified with the visible nucleus.

Telesco, C. M.↗
NASA NTRS1980

The diffuse gamma-ray background in the Hoyle-Narlikar cosmology

The paper analyzes the contributions of QSOs, BL-Lac objects and Seyfert galaxies to the diffuse gamma-ray background within the framework of the Hoyle-Narlikar theory. It is shown that the inconsistency reported in standard theory, namely that the evolutionary function needed to explain the gamma-ray data is very different from the one derived from the optical part of the spectrum, is no longer present. It is also shown that the contribution of a variable gravitational 'constant' to the expression for the diffuse background is the same as that of a density evolution function.

Canuto, V. M.↗
NASA NTRS1980

X-ray variability in active galaxy nuclei and quasars in less than one day

Data obtained from the Einstein Observatory demonstrating variations in X-ray emission from the nuclei of active galaxies and quasars on time scales of hours rather than previously observed days or years is presented. Light curves obtained from the Einstein imaging proportional counter for the Seyfert 1 galaxy NGC 6814 and from the High Resolution Imager for the quasars OX 169 and 3C 273 are illustrated, and variations by factors greater than two on time scales less than 20,000 sec for the first two objects and by a factor of 10% on a time scale over 50,000 sec for 3C 273 are pointed out. The measurements are also used to determine that thermal bremsstrahlung cannot be the cause of the intensity decay in OX 169, and that, in the absence of relativistic effects, the efficiency for energy release in the matter involved in the emission of 3C 273 is at least 0.1.

Elvis, M.↗
NASA NTRS1980

X-ray studies of quasars and active galaxies with the Einstein Observatory

Preliminary results of the first six months of an X-ray survey of active galaxies and quasars performed with the imaging proportional counter on board the Einstein Observatory are presented. Consideration is given to detections of Seyfert galaxies, N galaxies, BL Lac objects and quasars, and properties of selected representative objects are discussed in detail. The statistical properties, including class averages and correlation coefficients, of the various X-ray active galaxies are calculated in an attempt to determine the relation of X-ray properties to the similarities and differences between the various classes of galaxies. Evidence is obtained for a continuity of high-energy behavior among all active galaxies, and it is noted that they all exhibit flux variability, often on a short time scale. The soft X-ray emission can be explained in terms of the synchrotron self-Compton model, or alternatively by thermal emission from hot gas. A significant correlation is obtained between the X-ray and optical fluxes for all objects considered, indicating that optical quasar counts may be used to infer the contribution of quasars to the diffuse X-ray background.

Ku, W. H.-M.↗
NASA NTRS1980

Einstein observations of active galaxies

X-ray observations of Cen A (NGC 5128) and seven other X-ray emitting active galaxies are discussed which were made with the imaging proportional counter and the high-resolution imager aboard the Einstein Observatory. In addition to Cen A, the sources observed were the N-type galaxy 3C 120, the quasars OX 169 and 3C 273, and four Class 1 Seyfert galaxies, viz., Mkn 509, Mkn 79, NGC 6814, and NGC 4151. For Cen A, it is found that the X-ray data are dominated by a central point source of about 2 cts/sec, that X-ray elongations (possibly associated with the inner radio lobes) extend in the NE and SW directions, and that an X-ray jet exists which is aligned with the optical jet. The results for the other sources are used to derive emitting-region sizes and black-hole masses for models based on an accreting central black hole.

Tananbaum, H.↗
NASA NTRS1981

Optical identification of serendipitous Einstein sources - 19 X-ray-selected active galactic nuclei

The identification of counterparts to 19 serendipitous Einstein Observatory X-ray sources at high galactic latitude is reported. The counterparts are identified as previously uncataloged active galactic nuclei (AGNs) - quasars or Seyfert galaxies - with redshifts varying from z = 0.036 through z = 1.40. The success rate, that is, the fraction of X-ray sources that are identified as AGNs, is approximately 50%, an order of magnitude larger than for traditional ultraviolet surveys. It is expected that this method will produce a large number of X-ray-selected AGNs for statistical studies. For the 19 AGNs in this sample, which is free from the radio selection effects that have complicated previous studies, the X-ray-to-optical-flux slope is found to be 1.30 + or - 0.05.

Chanan, G. A.↗
NASA NTRS1981

Nonthermal hard X-ray emission from the nucleus of NGC 1275

Observations confirming the HEAO 1 discovery of a hard X-ray component in the X-ray spectrum of the Perseus cluster are reported. A comparison of the results with 1978 HEAO 1 observations and 1974 balloon limits shows that this component is variable on a time scale of one year. Synchrotron self-Compton models of the compact radio source centered on the nucleus of NGC 1275 predict a substantial secondary X-ray flux based on the observed radio data. While the observed X-ray flux is one-fourth the predicted value, uncertainties in the radio data are sufficient to account for the discrepancy. It is concluded that the hard X-ray flux originates in the active nucleus of the Seyfert galaxy NGC 1275 through the synchrotron self-Compton process.

Rothschild, R. E.↗
NASA NTRS1981

Radiation force on a relativistic plasma and the Eddington limit

Calculations of the radiation force due to Thomson scattering on a relativistic plasma are presented and discussed in relation to certain astronomical objects which operate within a few orders of magnitude of their Eddington luminosity. The radiation force on a hot isotropic plasma is shown to exceed that on a cold plasma by a factor depending on the electron Lorentz factor, which can be substantial in a relativistic plasma. In such a plasma, radiative bulk acceleration is found to occur through the anisotropic loss of internal energy during the Thomson scattering, resulting in an effect termed a Compton rocket. The Compton rocket is shown to be a relevant acceleration mechanism in situations where a relativistic electron plasma lies in the vicinity of a luminous source operating near the classical Eddington limit, including compact galactic X-ray sources and objects associated with active galactic nuclei (quasars, blazars, and Seyfert nuclei).

Odell, S. L.↗
NASA NTRS1981

Observations of faint Haro galaxies

Spectroscopic and photometric data for 23 faint-compact UV-excess galaxy candidates, found by Haro's three-color technique (1956), are presented. Eighteen were found to be emission-line galaxies (magnitudes between 14.4 and 17.9) with redshifts in the range of 1670 to 39,450 km/s; the remaining five appear to be stars. The apparent compactness of the galaxy images is a result of the finite resolution of the Survey plates. Faint Haro galaxies are not distinguishable from the original Haro galaxies in surface brightness or in their range of color and absolute magnitude. The Haro galaxies correspond to roughly two-thirds of Huchra's non-Seyfert Markarian galaxies (1977 a) which have the most negative (U-B) index; the new Haro galaxies have the same V magnitude growth with aperture, the same (B-V) aperture relation, and the same mean surface brightness as the Markarian galaxies.

Kinman, T. D.↗
NASA NTRS1981

Galaxies

Normal galaxies, radio galaxies, and Seyfert galaxies are considered. The large magellanic cloud and the great galaxy in Andromedia are highlighted. Quasars and BL lacertae objects are also discussed and a review of the spectral observations of all of these galaxies and celestial objects is presented.

Source record↗
NASA NTRS1982

The absence of rapid X-ray variability in active galaxies

Variations on time scales ranging from minutes to several hours in the X-ray flux from 54 observations of 38 active galaxies are identified. The sample is composed mostly of Seyfert I galaxies but also includes radio galaxies, NELG's BL Lacs and 3C 273. Only NGC 6814 varied on time scales as short as 100 sec. No other source was observed to vary with a time scale of less than 12 hours. Large amplitude short term variations are not a characteristic of the X-ray emission from active galaxies. Upper limits on sigma sub I/I ranged from 2% for Cen A, 5% for NGC 4151, to approximately 20% for sources giving 1 ct/sec in the detector. Three objects NGC 3227, NGC 4151 and MCG 5-23-16 show variability consistent with a time scale of approximately 1 day. Ways to reconcile the rapid variability seen for NGC 6814 (and NGC 4051) with the general stability observed for the other objects are considered.

Tennant, A. F.↗
NASA NTRS1982

Time variations in C IV lambda 1550 and Ly alpha emission lines in NGC5548

Two short-wavelength images of NGC5548 were obtained and separated by a three month interval. Combining this data with that obtained by Wu et al. One year prior to the first image, time variations were discovered in the C IV lambda 1550 and Ly alpha profiles as well as in the intensity ratio. In the image obtained in November 1980, the C IV profile is essentially the same as that of WU et al. However, the November Ly alpha profile is substantially narrower and the Ly alpha to C IV intensity ratio is reduced by roughly a factor of 2. In our February, 1981 image, the C IV profile is narrowed by approximately a factor of 2 compared with the other two observations, while the Ly alpha profile and Ly alpha to C IV ratio is essentially the same as in November. Also a short-wavelength image of the very bright Seyfert galaxy Fairall 9 were obtained an it was found that the C IV and Ly alpha lines in this object have essentially identical profiles.

Ptak, R.↗
NASA NTRS1982

Distribution of gas in the halo of the galaxy

Results are presented from a high-resolution, ultraviolet study of interstellar gas situated away from the plane of the Milky Way Galaxy, using the nuclei of Seyfert galaxies Mkn 509 and F9 as background probes. In these directions, low-velocity, galactic gas were detected as well as two extragalactic clouds, one probably associated with the Magellanic Stream and the other with Mkn 509. These data were combined with results from other lines of sight to show that the ultraviolet species extend about 10 kpc from the plane, assuming the high-latitude gas corotates with the galactic disk. Complimentary observations of the optical Ca II and Na I species suggests that these do not extend as far - perhaps 2 to 3 kpc from the plane. Further, the exceedingly complex velocity structure found only in Magellanic Cloud directions suggests that these sight-lines are not typical of high-latitude gas in general.

Blades, J. C.↗