Physics
Scientific paper
Feb 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........75l&link_type=abstract
Thesis (PH.D.)--MONTANA STATE UNIVERSITY, 1991.Source: Dissertation Abstracts International, Volume: 52-12, Section: B, page: 64
Physics
1
Galactic Nuclei
Scientific paper
Previously, iron features were not known to be a common feature of the X-ray spectra of Active Galactic Nuclei (AGN). The data from a long observation of NGC 5506 performed by EXOSAT were reanalyzed, and an emission line and an absorption edge were found. Subsequently, 47 X-ray spectra from a sample of 40 AGN observed with EXOSAT were reanalyzed. Evidence for line emission was found in 13 spectra from 12 sources; however, the line intensities were not well determined. X-ray variability is an interesting feature of some low luminosity Seyfert 1 galaxies. As part of Tsuruta's simultaneous multi-frequency campaign, the Seyfert 1 nuclei NGC 7469 and NGC 6814 were observed with the LAC onboard Ginga. These data were analyzed along with a second Ginga observation of NGC 6814. The flux level of NGC 7469 was low and the satellite pointing was not stable, making detailed analysis difficult. The flux level was seen to decrease during the second day of observation with a halving time scale of 25,000 seconds. The photon index was remarkably flat. From the two observations of NGC 6814, a wealth of interesting results emerged. The rapid flux variability with time scale of ~300 seconds and the 12000 second periodicity characteristic of this unusual source were confirmed in both observations. During the first observation, periodic dips were found, in which the flux fell to nearly zero. Spectral variability was confirmed during these dips, as well as a decrease in line emission. During the second observation, periods of rapid flux increase and decrease were found, and spectral variability was again found. Well defined energy delays were also discovered. A variable absorption model was explicitly fit to the delay data. This model could successfully though qualitatively explain the spectral variability during the regions of fastest variability. In the intense radiation field of an AGN,the motion of particles is influenced by the gravitational and radiation fields. To explore the motion of such particles, a spherically symmetric model by Abramowicz et al. 1990 was extended to a more realistic case by using a modified radiation stress energy tensor. This modification produced a significant change in the character of the critical point solutions.
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