X-Ray and Ultraviolet Observations of BL Lacertae Objects
Abstract
Five X-ray bright BL Lacertae objects, PKS 0548 -322, Mrk 421, 1218+304, Mrk 501, and PKS 2155-304, have been studied with X-ray and ultraviolet spectroscopic detectors on three satellites. The data include HEAO-1 A2 observations of PKS 2155-304; HEAO-2 SSS observations of all five objects; and IUE observations of PKS 0548-322 and PKS 2155-304. Analysis of these data indicates six principal results. First, with one exception, all spectra are well fit by single component power law models. The exception is the A2 pointing spectrum of PKS 2155-304, which requires a two-component model. Second, the X-ray and ultraviolet spectra are characterized by a lack of strong emission or absorption features. Third, the ultraviolet and X-ray spectra appear to be smoothly connected, implying the existence of a common emission mechanism. Fourth, the intensities are highly variable, more so in the X-ray than in the ultraviolet. Fifth, the ultraviolet spectral shape is only slightly variable, while the X-ray spectral shape is more strongly variable. Sixth, the connection between changes in spectral shape and intensity is not clear but in most cases, the observed X-ray variability is adequately explained by invoking changes in the relative strengths of two components. The broad band, radio-through-X-ray spectra can be well fit by a synchrotron self-Compton (SSC) model that allows for relativistic bulk motion. SSC analysis of BL Lac objects indicates that high Doppler beaming factors may be characteristic of the class. A second observational test of the jet hypothesis for BL Lac objects (Blandford and Rees 1978) is the identification of the parent population. Contrary to previous assumptions, the ratio of volume densities of BL Lac and parent objects is a strong function of observed luminosity. The optical and X-ray luminosity functions for BL Lac objects are estimated, and are compatible with, but not well constrained by, the theory. Simple arguments about the luminosity and line emission in BL Lac objects confirm the suggestion of Schwartz and Ku (1983) that low luminosity radio galaxies may be the parent population.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1984
- Bibcode:
- 1984PhDT.........1U
- Keywords:
-
- RELATIVISTIC JETS;
- LUMINOSITY FUNCTIONS;
- SYNCHROTRON SELF-COMPTON FORMULAE;
- Physics: Astronomy and Astrophysics;
- Bl Lacertae Objects;
- Spaceborne Astronomy;
- Ultraviolet Spectra;
- X Ray Spectra;
- Absorption Spectra;
- Emission Spectra;
- Heao 1;
- Heao 2;
- Iue;
- Luminosity;
- Radio Galaxies;
- Astronomy