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M. Boettcher (Rice University), C. D. Dermer (NRL)
Blazar subclasses ranging from flat-spectrum radio quasars (FSRQs) through low-frequency-peaked BL Lac objects (LBLs) to high-frequency-peaked BL Lac objects (HBLs) exhibit a sequence of increasing spectral hardness with decreasing luminosity that cannot be explained solely by orientation effects. Using an analytic model for the relativistic electron energetics and broadband emission from blazar jets, we propose an evolutionary scenario that links these blazar subclasses by means of a reduction of the black-hole accretion power with time. As the circumnuclear material accretes to fuel the central engine, less gas and dust is left to scatter accretion-disk radiation and produce an external Compton-scattered component in blazar spectra. This evolutionary trend produces the sequence FSRQ -> LBL -> HBL. Such a scenario may also link radio-loud AGNs with ultraluminous infrared galaxies and radio-quiet optical QSOs, if those objects constitute the high Eddington-ratio epoch of supermassive black hole growth, as suggested by the observed anti-correlation between radio and soft X-ray activity in some Galactic black-hole candidates, possibly due to the quenching of radio jet formation at near-Eddington accretion rates.
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The author(s) of this abstract have provided an email address for comments about the abstract: mboett@spacsun.rice.edu