X-ray studies of BL Lacertae objects

This thesis presents spectral x-ray data for BL Lac objects observed by the IPC and MPC aboard the Einstein Observatory and interprets that data in a context of their overall radiation spectra using synchrotron and synchrotron self-Compton models. The objects considered are: OJ 287, PKS 0735 + 178, I Zw 186, PKS 0548-322, Mkn 180, BL Lacertae, PKS 2155-304, H 0414-009 and H 0323 + 022. X-ray spectra of BL Lac objects are well described by a power law model with a low energy cutoff due to absorption within the own Galaxy. The best fit values of the energy spectral index α in the IPC (0.2-4.0 keV) band range from 0.73 to 2.35, with a mean of 1.2 and rms spread of 0.51. No single, universal index can fit the spectra of all objects. For all objects except PKS 0735 + 178, the x-ray spectrum is an extrapolation of the infrared/optical UV spectrum; in PKS 0735 + 178, the x-ray spectrum lies significantly below such an extrapolation. The overall electromagnetic distribution in those objects is interpreted as arising due to the synchrotron process in at least two spatial regions, with sizes respectively ∼1018 cm for the radio component and ∼1016 cm for the optical component. In objects where the x-ray spectrum lies on the extrapolation of the infrared-optical-ultraviolet spectrum, the x-ray emission is interpreted also to be due to the synchrotron process