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      Variability along the Blazar-Sequence - Hints for extragalactic Cosmic Rays?

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          Abstract

          The spectral energy distribution and variability of several blazars (Mkn 501, 1 ES 2344+51.4, PKS 2155-30.4, 1 ES 1218+30.4, 3C 454.3) along the blazar sequence is investigated using a selfconsistent and timedependent lepto-hadronic hybrid emission model. The BL Lac objects in the list are successfully modelled with purely leptonic radiation processes (essentially Synchrotron Self-Compton emission), while the Flat Spectrum Radio Quasar requires highly relativistic hadrons to be present within the jet. Variability is exploited as well with our model to distinguish between Self-Compton and hadronic gamma radiation making use of their different signatures in lightcurves. As a consequence active galactic nuclei with z > 0.5 are the best candidates as sources of extragalactic consmic rays, since High-Peaked BL Lac objects do not seem to accelerate protons to energies above thermal. Furthermore the parameters found during the modelling of the objects agree very well with obervations of e.g. superluminal motion or typical variability timescales.

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          Energy Loss of High-Energy Cosmic Rays in Pair-Producing Collisions with Ambient Photons

          George R. Blumenthal (1970)
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            BeppoSAX Observations of Unprecedented Synchrotron Activity in the BL Lac Object Mkn 501

            Giuseppe Vacanti, Gianpiero Tagliaferri, Aldo Treves … (1997)
            The BL Lac object Mkn 501, one of the only three extragalactic sources (with Mkn 421 and 1ES 2344+514) so far detected at TeV energies, was observed with the BeppoSAX satellite on 7, 11, and 16 April 1997 during a phase of high activity at TeV energies, as monitored with the Whipple, HEGRA and CAT Cherenkov telescopes. Over the whole 0.1-200 keV range the spectrum was exceptionally hard (alpha =< 1, with F_nu ~ nu^{-alpha}) indicating that the X-ray power output peaked at (or above) ~100 keV. This represents a shift of at least two orders of magnitude with respect to previous observations of Mkn 501, a behavior never seen before in this or any other blazar. The overall X-ray spectrum hardens with increasing intensity and, at each epoch, it is softer at larger energies. The correlated variability from soft X-rays to the TeV band points to models in which the same population of relativistic electrons produces the X-ray continuum via synchrotron radiation and the TeV emission by inverse Compton scattering of the synchrotron photons or other seed photons. For the first time in any blazar the synchrotron power is observed to peak at hard X-ray energies. The large shift of the synchrotron peak frequency with respect to previous observations of Mkn 501 implies that intrinsic changes in the relativistic electron spectrum caused the increase in emitted power. Due to the very high electron energies, the inverse Compton process is limited by the Klein-Nishina regime. This implies a quasi-linear (as opposed to quadratic) relation of the variability amplitude in the TeV and hard X-ray ranges (for the SSC model) and an increase of the inverse Compton peak frequency smaller than that of the synchrotron peak frequency.
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              Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects

              Markus Boettcher, Charles Dennison Dermer, Justin Finke (2008)
              We introduce a methodology for analysis of multiwavelength data from X-ray selected BL Lac (XBL) objects detected in the TeV regime. By assuming that the radio--through--X-ray flux from XBLs is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly oriented magnetic field of a relativistic blazar jet, we obtain the electron spectrum. This spectrum is then used to deduce the synchrotron self-Compton (SSC) spectrum as a function of the Doppler factor, magnetic field, and variability timescale. The variability timescale is used to infer the comoving blob radius from light travel-time arguments, leaving only two parameters. With this approach, we accurately simulate the synchrotron and SSC spectrum of flaring XBLs in the Thomson through Klein-Nishina regimes. Photoabsorption by interactions with internal jet radiation and the intergalactic background light (IBL) is included. Doppler factors, magnetic fields, and absolute jet powers are obtained by fitting the {\em HESS} and {\em Swift} data of the recent giant TeV flare observed from \object{PKS 2155--304}. For the contemporaneous {\em Swift} and {\em HESS} data from 28 and 30 July 2006, respectively, Doppler factors \(\gtrsim 60\) and absolute jet powers \(\gtrsim 10^{46}\) ergs s\(^{-1}\) are required for a synchrotron/SSC model to give a good fit to the data, for a low intensity of the IBL and a ratio of 10 times more energy in hadrons than nonthermal electrons. Fits are also made to a TeV flare observed in 2001 from Mkn 421 which require Doppler factors \(\gtrsim 30\) and jet powers \(\gtrsim 10^{45}\) erg s\(^{-1}\).
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                Author and article information

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                Publication date Created: 09 September 2011
                Article
                ArXiV ID: 1109.1975
                SO-VID: cc484a92-f5a6-4091-99c9-f3251e8e6566
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                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Comments 4 pages, 3 figures. Contribution to the 32nd ICRC, Beijing, #0019. To appear in the proceedings
                Categories astro-ph.HE

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