Journal Article

The blazar sequence: a new perspective

G. Ghisellini and F. Tavecchio

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 387, issue 4, pages 1669-1680
Published in print July 2008 | ISSN: 0035-8711
Published online July 2008 | e-ISSN: 1365-2966 | DOI:
The blazar sequence: a new perspective

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We revisit the so-called ‘blazar sequence’, which connects the observed bolometric luminosity to the shape of the spectral energy distribution (SED) of blazars. We propose that the power of the jet and the SED of its emission are linked to the two main parameters of the accretion process, namely the mass of the black hole and the accretion rate. We assume (i) that the jet kinetic power is proportional to the mass accretion rate; (ii) that most of the jet dissipation takes place at a distance proportional to the black hole mass; (iii) that the broad line region exists only above a critical value of the disc luminosity, in Eddington units, and (iv) that the radius of the broad line region scales as the square root of the ionizing disc luminosity. These assumptions, motivated by existing observations or by reasonable theoretical considerations, are sufficient to uniquely determine the SED of all blazars. This framework accounts for the existence of ‘blue quasars’, i.e. objects with broad emission lines but with SEDs resembling those of low-luminosity high-energy peaked BL Lacertae (BL Lac) objects, as well as the existence of relatively low-luminosity ‘red’ quasars. Implications on the possible evolution of blazars are briefly discussed. This scenario can be tested quite easily once the AGILE and especially the GLAST satellite observations, coupled with information in the optical/X-ray band from Swift, will allow the knowledge of the entire SED of hundreds (and possibly thousands) blazars.

Keywords: radiation mechanisms: non-thermal; BL Lacertae objects: general; quasars: general; gamma-rays: theory; X-rays: general

Journal Article.  9856 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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