Gamma rays from blazars

Abstract

Abstract. Blazars are high-energy engines providing us natural laboratories to study particle acceleration, relativistic plasma processes, magnetic field dynamics, black hole physics. Key informations are provided by observations at high-energy (in particular by Fermi/LAT) and very-high energy (by Cherenkov telescopes). I give a short account of the current status of the field, with particular emphasis on the theoretical challenges connected to the observed ultra-fast variability events and to the emission of flat spectrum radio quasars in the very high energy band.

Laminar and Turbulent Dynamos in Chiral Magnetohydrodynamics. II. Simulations

“…Under the assumption that the spectrum of the cosmic magnetic field is sharply peaked at some scale ξ 0 (as is the case in all of the simulations presented here), the lower bounds on magnetic fields, inferred from the nonobservation of GeV cascades from TeV sources (Neronov & Vovk 2010;Tavecchio et al 2010;Dolag et al 2011) can be directly translated into a bound on magnetic helicity today. The observational bound scales as |B| ∝ ξ −1/2 0 for ξ 0 < 1 Mpc (Neronov & Vovk 2010) and therefore B 2 ξ 0 = const > 8 × 10 −38 G 2 Mpc.…”

“…The limit given by Equation (61) is quite general. It does not rely on chiral MHD or the CME, but simply reinterprets the bounds of Neronov & Vovk (2010), Tavecchio et al (2010), Dolag et al (2011), andDermer et al (2011) as bounds on magnetic helicity. Given such an interpretation, we conclude that if cosmic magnetic fields are helical and have a cosmological origin, then at some moment in the history of the universe the density of chiral charge was much larger than n γ (T ).…”

Intergalactic electromagnetic cascades in the magnetized Universe as a tool of astroparticle physics

“…The extended emission search technique is also sensitive to the PH pattern, but in this case only lower constraints on B could be derived [32]. b) A simplified method that relies solely on the spectral information inside the point spread function (PSF) of the instrument was, so far, the most popular technique [15,[46][47][48][49][50][51][52]. However, in this case a part of information is lost, and the results are less robust than for the case of the MBC search method; therefore, the systematic uncertainty of this approach is large, sometimes not even allowing to exclude the hypothesis of B=0 [53].…”

Primordial magnetic fields from gravitationally coupled electrodynamics in nonsingular bounce cosmology

“…. Hence, the mode today is 12) and the profile is |A k (η 0 )| |e 1 | 2 + |e 2 | 2 . The evolutions of A k and its time derivative A k are sketched in Fig.…”

“…By the recent CMB observations, the strength of the magnetic field is smaller than a few nano-gauss at the 1Mpc scale [10,11]. Additionally, the γ−ray detections of the distant blazars imply that the magnetic field should be larger than 10 −16 gauss on the scales 1 − 10 4 Mpc [1,2,[12][13][14][15]. Note that if alternative methods in data processing are used, the value of the lower limit 10 −16 gauss can be relaxed, for example, to 10 −18 gauss [2,14,16] and to 10 −19 gauss [17].…”