Statistics
Scientific paper
Jan 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994phdt........32p&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF COLORADO AT BOULDER, 1994.Source: Dissertation Abstracts International, Volume: 56-02, Section: B,
Statistics
3
Active Galactic Nuclei
Scientific paper
This thesis describes a multi-wavelength inquiry into the nature of BL Lacertae objects, perhaps the most enigmatic of all active galactic nuclei (AGN). This inquiry has taken several forms, as well as used several different observational techniques. Included herein is the testing of the most efficient method yet found to discover new BL Lac objects. This method makes use of the distinctive broad-band spectrum of BL Lac objects; 27 of 31 objects identified as candidates through the process were spectroscopically confirmed to be BL Lacs. Through using this method, the largest complete sample of BL Lacs known has been discovered; the characteristics of the sample are described in this thesis. A multitude of radio observations were also done, not only on the members of the new Slew Survey sample (such observations are essential to the technique used to find these new BL Lacs), but also on previously known X-ray selected and radio-selected BL Lacs. These observations have significantly bolstered the evidence that most BL Lacertae objects are beamed FR 1 radio galaxies in several ways. For example, BL Lacs are seen to have extended (unbeamed) radio power statistics typical of FR 1s, but significantly higher core powers (as the unified scheme predicts). X -ray selected BL Lacs (XBLs), which are 10-30 times more numerous than radio-selected BL Lacs (RBLs), are seen to be intermediate between FR 1s and RBLs in both radio core dominance and radio polarization fraction. Several individual XBLs show evidence for aligned subarcsecond radio structure and radio polarization PAs, as would be expected under unified schemes; however, we have insufficient evidence to say whether this exists as a general trend. We also delved into the enigmatic BL Lac object PKS 1413 + 135 via three different radio observations. These observations confirmed the presence of a large absorbing column in front of the BL Lac (earlier evidence of same had been seen in the X-ray spectrum), and also found the very first VLBI counterjet seen among BL Lacs! This feature is incompatible with unified schemes, and we believe PKS 1413 + 135 is an excellent candidate for a gravitationally lensed source. Finally, we analyzed the X-ray spectra of all 22 objects in the Complete Einstein Extended Medium Sensitivity Survey sample of XBLs. By doing so, we confirmed that XBLs are evolving negatively, opposite in sense to Quasars and also to RBLs. BL Lac X-ray spectra are steep, thus causing us to revive a model suggested by Guilbert, Fabian and McCray for the linelessness of these objects. We compare XBL soft X-ray spectra with several other varieties of AGN. The steepness of XBL spectra suggests that the X -ray spectra of BL Lacs are dominated by the steepening synchrotron tail, rather than inverse Compton radiation from the mm and radio jet. Finally, we examine the issue of the sample's possible incompleteness, and attempt to explain the discrepancy between RBL and XBL V/V max values.
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