X‐Ray Spectral Variability Signatures of Flares in BL Lacertae Objects

We are presenting a detailed parameter study of the time-dependent electroninjection and kinematics and the self-consistent radiation transport in jets ofintermediate and low-frequency peaked BL Lac objects. Using a time-dependent,combined synchrotron-self-Compton and external-Compton jet model, we study theinfluence of variations of several essential model parameters, such as theelectron injection compactness, the relative contribution of synchrotron toexternal soft photons to the soft photon compactness, the electron-injectionspectral index, and the details of the time profiles of the electron injectionepisodes giving rise to flaring activity. In the analysis of our results, wefocus on the expected X-ray spectral variability signatures in a region ofparameter space particularly well suited to reproduce the broadband spectralenergy distributions of intermediate and low-frequency peaked BL Lac objects.We demonstrate that SSC- and external-Compton dominated models for thegamma-ray emission from blazars are producing significantly differentsignatures in the X-ray variability, in particular in the soft X-ray lightcurves and the spectral hysteresis at soft X-ray energies, which can be used asa powerful diagnostic to unveil the nature of the high-energy emission from BLLac objects.Comment: 38 pages, including 17 figures; AASTeX 502 format. Accepted for publication in ApJ (vol. 581