Modelling of blazar SEDs with the nonlinear SSC cooling process

Observations of blazar flaring states reveal remarkably different variability time scales. Especially rapid flares with flux doubling time scales of the order of minutes have been puzzling for quite some time. Many modeling attempts use the well known linear relations for the cooling and emission processes in the jet in a steady-state scenario, albeit the obvious strongly time-dependent nature of flares. Due to the feedback of self-produced radiation with additional scattering by relativistic electrons, the synchrotron-self Compton (SSC) effect is inherently time-dependent. Although this feedback is usually implemented in numerical treatments, only recently an analytical analysis of the effects of this nonlinear behaviour has been performed. Here, we report our results concerning the effect of the time-dependent SSC on the spectral energy distribution (SED) of blazars. We calculated analytically the synchrotron and the SSC component, giving remarkably different spectral features compared to the standard linear approach. Adding an external photon field to the original setting, we could implement quite easily the effect of an additional external Compton (EC) cooling, since such strong external photon fields are observed in flat spectrum radio quasars (FSRQ), a subclass of blazars. Calculating the resulting flux due to the EC cooling, we were able to show that the resulting inverse Compton component strongly depends on the free parameters, and that SSC could potentially have a strong effect in FSRQs, contrary to what is usually assumed.Comment: Contribution to the GAMMA2012 conference in Heidelberg, to be published in the AIP Proceedings "High Energy Gamma-Ray Astronomy, eds. F. Aharonian, W. Hofmann, F. Rieger

Focused acceleration of cosmic-ray particles in non-uniform magnetic fields

The Fokker–Planck equation for cosmic-ray particles in a spatially varying guide magnetic field in a turbulent plasma is analyzed. An expression is derived for the mean rate of change of particle momentum, caused by the effect of adiabatic focusing in a non-uniform guide field. Results of an earlier diffusion-limit analysis are confirmed, and the physical picture is clarified by working directly with the Fokker–Planck equation. A distributed first-order Fermi acceleration mechanism is identified, which can be termed focused acceleration. If the forward and backward-propagating waves have equal polarizations, focused acceleration operates when the net cross helicity of an Alfvenic slab turbulence is either negative in a diverging guide field or positive in a converging guide field. It is suggested that focused acceleration can contribute to the formation of the anomalous cosmic-ray spectrum at the heliospheric termination shock

A Gaussian Model for the Time Development of the Sars-Cov-2 Corona Pandemic Disease. Predictions for Germany Made on 30 March 2020

For Germany, it is predicted that the first wave of the corona pandemic disease reaches its maximum of new infections on 11 April 2020 −3.4+5.4 days with 90% confidence. With a delay of about 7 days the maximum demand on breathing machines in hospitals occurs on 18 April 2020 −3.4+5.4 days. The first pandemic wave ends in Germany end of May 2020. The predictions are based on the assumption of a Gaussian time evolution well justified by the central limit theorem of statistics. The width and the maximum time and thus the duration of this Gaussian distribution are determined from a statistical χ2 -fit to the observed doubling times before 28 March 2020

Gamma rays from extragalactic radio sources

It is proposed that the important connection between 3C 273 and 3C 279, the first two extragalactic sources detected at greater than 100 MeV energies, is their superluminal nature. In support of this conjecture, we propose a radiation mechanism that focuses gamma rays in the superluminal direction, due to Compton scattering of accretion-disk photons by relativistic nonthermal electrons in the jet