Letter to the Editor
Power for dry BL Lacertae objects
Dipartimento di Fisica, Università di Roma “Tor Vergata”, and INFN Roma Tor Vergata via della Ricerca Scientifica 1, 00133 Roma, Italy e-mail: email@example.com
2 INAF/IASF-Roma, via Fosso del Cavaliere 1, 00100 Roma, Italy
Accepted: 16 November 2009
Is it significant that the intrinsic outputs of several BL Lacs are observed to level off at values of about erg s-1? In searching for an answer, we compare γ-ray observations by the AGILE satellite of the BL Lac S5 0716+714 with those of Mrk 421 and Mrk 501; the former are particularly marked by intense flares up to fluxes of photons cm-2 s-1 in the GeV energy range. These “dry” BL Lacs show evidence of neither thermal disk emissions nor emission lines signaling any accreting or surrounding gas; the spectral distributions of their pure non-thermal radiations are effectively represented by the synchrotron self-Compton process. With source parameters correspondingly derived and tuned with simultaneous multiwavelength observations, we find for S5 0716+714 a total jet power of about erg s-1, which makes it one of the brightest dry BL Lacs so far detected in γ rays. We evaluate the mass of the associated Kerr hole to be around , implying that the source is significantly gauged in terms of the maximal power around erg s-1 extractable via the Blandford-Znajek electrodynamical mechanism; other dry BL Lacs observed in γ rays remain well below that threshold. These findings and those forthcoming from Fermi-LAT will provide a powerful test of electrodynamics in the surroundings of the hole, that are dominated by GR effects.
Key words: BL Lacertae objects: general / radiation mechanisms: non-thermal / black hole physics / accretion, accretion disks
© ESO, 2009