Particle diffusion and localized acceleration in inhomogeneous AGN jets – II. Stochastic variation

Abstract

We study the stochastic variation of blazar emission under a 2-D spatially resolved leptonic jet model we previously developed. Random events of particle acceleration and injection in small zones within the emission region are assumed to be responsible for flux variations. In addition to producing spectral energy distributions that describe the observed flux of Mrk 421, we further analyze the timing properties of the simulated light curves, such as the power spectral density (PSD) at different bands, flux-flux correlations, as well as the cross-correlation function between X-rays and TeV γ-rays. We find spectral breaks in the PSD at a timescale comparable to the dominant characteristic time scale in the system, which is usually the predefined decay time scale of an acceleration event. Cooling imposes a delay, and so PSDs taken at lower energy bands in each emission component (synchrotron or inverse Compton) generally break at longer timescales. The flux-flux correlation between X-rays and TeV γ-rays can be either quadratic or linear, depending on whether or not there are large variation of the injection into the particle acceleration process. When the relationship is quadratic, the TeV flares lag the X-ray flares, and the optical & GeV flares are large enough to be comparable to the ones in X-ray. When the relationship is linear, the lags are insignificant, and the optical & GeV flares are small.

The Great Markarian 421 Flare of 2010 February: Multiwavelength Variability and Correlation Studies

“…A recent study of Mrk 421 flares extracted from archival XMM-Newton X-ray data spanning 2000-2017 is consistent with the expectations for an SOC model, thus lending support to the magnetic reconnection process driving blazar flares (Yan et al 2018). Additionally, the flatness of the PSD indicates that the turn-on/turn-off timescale of mini-flares can be below 1 hr and generally has a wide probability distribution extending from subhour timescales to entire nights (Chen et al 2016).…”

Modelling the coincident observation of a high-energy neutrino and a bright blazar flare

“…The model SED is then fitted to that observed. The flare is initiated in a smaller core in the radiation zone that characterizes the quiescent state, and both contribute to the observed emission in a superimposed way, a scenario that mimics localized particle acceleration and subsequent diffusive transport into a larger emission zone (25,26). The radiation from the core is significantly brighter, rendering the presence of the larger (quiescent) zone insignificant.…”

Multiband variability studies and novel broadband SED modeling of Mrk 501 in 2009

“…We found that none of the tested models could satisfactorily reproduce the changes observed in the spectral distribution. This broadband SED can be explained with more sophisticated theoretical models, like the inhomogeneous time-dependent models reported in Ghisellini et al (2005), Graff et al (2008), Chen et al (2011Chen et al ( 2015Chen et al ( , 2016, which provide a more elaborate physical scenario, at the expense of an increase in the number of degrees of freedom of the model. However, a caveat has to be taken into account when interpreting these results, which is the lack of strict simultaneity of the different data sets, in particular the Swift/XRT and the VHE γ-ray data.…”