Synchrotron self-Compton flaring of TeV blazars

Abstract

The vast improvement of the sensitivity of modern ground-based air Cherenkov telescopes, together with the sensitive flux measurements at lower frequencies, requires accurate elaborations of the theoretical radiation models for flaring blazars. Here the flaring of TeV blazars due to the synchrotron-self Compton (SSC) process is considered. We assume that, at the moment t = t 0 , a flare in the emission knot occurs due to the instantaneous injection of monoenergetic (E 0 ) ultrarelativistic electrons. The ultrarelativistic electrons are injected uniformly over the knot volume and at later times are subject to linear synchrotron radiation cooling in a magnetic field whose strength remains constant during the time evolution of the relativistic electrons.The generated synchrotron photons are subject to multiple Thomson-scattering off the cold electrons in the source giving rise to spatial photon diffusion. Optically thick and thin synchrotron radiation intensities and photon density distributions in the emission knot as functions of frequency and time are analytically determined. The synchrotron photons serve as target photons for the SSC process, which is calculated in the optically thin frequency range using the Thomson approximation of the inverse Compton cross section. It is shown that the optically thick part of the synchrotron radiation process provides a negligible contribution to the resulting SSC intensity at all frequencies and times.Because the high-energy TeV photons undergo no elastic multiple Compton scatterings, we neglect the influence of photon diffusion in the calculation of the SSC intensity and fluence distribution with energy. The SSC fluence exhibits a break at E f = 15.8bGeV from a ∝E −1/4 s -power law spectrum at lower photon energiesThe application to the observed TeV fluence spectrum of the flare of PKS 2155-304 on July 28, 2006 yields δb −1/3 = 27.1 ± 6.5. The emergent SSC light curve is independent of spatial photon diffusion and determined by the temporal variations on the relativistic electron density distribution and the synchrotron photon density. The comparison of the observed with the theoretical monochromatic synchrotron light curve determines the photon escape distribution.

Synchrotron self-Compton flaring of TeV blazars

“…For energies much lower than the characteristic energy s < L,NL f , we find the same solutions as in Schlickeiser & Röken (2008) and as in Sect. 6, leading to the conclusion that the fluence behaviour for s < L,NL k,max is identical to the δ-distribution-approximated …”

“…Mastichiadis & Kirk (1997), Dermer et al (1997), Chiaberge & Ghisellini (1999), Sokolov et al (2004) and Böttcher (2007). Here, we investigate analytically the influence of a nonlinear electron synchrotron cooling on the synchrotron self-Compton process following the analysis of the flaring of TeV blazars due to the synchrotron self-Compton process for a linear synchrotron radiation cooling behaviour of the injected electrons (Schlickeiser & Röken 2008), where a δ-distribution approximation (Reynolds 1982;Dermer & Schlickeiser 1993) was used for the computation of the inverse Compton scattering rateṅ s . Most of the calculations of photon spectra modelling quantities have been based on such rather simple approximations.…”

A new ordering parameter of spectral energy distributions from synchrotron self-Compton emitting blazars

“… The Thomson energy (), which denotes the maximum initial scattered photon energy in the Thomson limit. The Schlickeiser–Röken (SR) break energy, introduced first by Schlickeiser & Röken (2008), which depends weakly (∝ b −1/3 ) on the magnetic field strength. The initial electron injection Lorentz factor γ 0 = 10 4 γ 4 . The characteristic electron Lorentz factor (), that is, γ B = 217 R 15 / N −1/2 50 =γ 0 /α. …”

“…The Schlickeiser–Röken (SR) break energy, introduced first by Schlickeiser & Röken (2008), which depends weakly (∝ b −1/3 ) on the magnetic field strength.…”

Retardation of non-thermal photon light curves from flaring blazars

“…Recently, Schlickeiser & Röken (2008 -hereafter referred to as SR) have investigated the synchrotron and synchrotron-self Compton (SSC) flaring of blazars due to relativistic electrons, including processes (1) and (3). They assumed that at the moment t = t 0 monoenergetic ultrarelativistic electrons were instantaneously injected uniformly over the knot volume.…”