arXiv subjects

A. Mastichiadis

Publications and source records attributed to A. Mastichiadis.

40 records · Page 3Linked to original sources

arXiv1996

On the production of very high energy beamed gamma-rays in blazars

The variable flux of TeV gamma-rays detected from Mkn 421 and Mkn 501 requires the presence of high energy electrons, which could in principle produce large numbers of electron/positron pairs, leading to an electromagnetic cascade. We point out that this scenario can be avoided if electrons are accelerated to high energy rectilinearly, rather than being injected isotropically into a blob, as in most of the models of the GeV gamma-ray emission. By balancing linear acceleration by an electric field against inverse Compton losses in the radiation field of the accretion disk we calculate the emitted spectra and find the conditions which must be fulfilled in order to exclude the development of electromagnetic cascades during acceleration. Assuming these to be fulfilled, we show that the maximum possible photon energy is approximately $10M_8^{2/5}\,$TeV, where $M_8$ is the mass of the central black hole in units of $10^8\,\msolar$. In addition we compute the optical depth to absorption of TeV photons on a possible isotropic scattered component and on the observed nonthermal radiation (in the case of Mkn 421) and find that TeV photons can escape provided the nonthermal X-rays originate in a jet moving with a Lorentz factor of around 8.

astro-ph↗

arXiv1996

On the high energy non-thermal emission from shell-type supernova remnants

Shock waves associated with shell type supernova remnants are considered to be possible sites of cosmic ray acceleration. Since shocks are capable of accelerating electrons in addition to protons one anticipates both species to contribute to the high energy radiation expected from these objects. Adopting a simple model for particle acceleration we calculate in a self-consistent manner the time-dependent synchrotron and inverse Compton radiation of high energy electrons assumed either to be accelerated directly by the shock wave or to be injected at high energies as secondaries from the hadronic collisions of relativistic protons with the circumstellar material. We deduce that for standard supernova parameters the TeV flux produced from neutral pion decay is about the same order as the flux expected from directly accelerated electrons.

astro-ph↗

arXiv1994

The effect of triplet production on pair-Compton cascades in thermal radiation

We calculate the spectrum of photons resulting from electromagnetic cascades through thermal radiation, and examine the consequences of including triplet production in these cascades. We assume that the cascade is one-dimensional, and we find that this approximation is justified in the present work for thermal radiation with temperature less than $10^{-3} mc^2$. Results are obtained for both monoenergetic and power-law primary spectra, and for a variety of path lengths. We find that triplet production is particularly important in electron--photon cascades through thermal radiation when the primary energy exceeds $10^5 m^2c^4/kT$ for propagation over small path lengths. The importance of triplet production decreases as the path length increases, and it has no effect on saturated cascades.

astro-ph↗

arXiv1994

"The Contribution of Active Galactic Nuclei to the Diffuse Gamma Ray Background"

We consider the emission of high energy to very high energy $γ$-rays in radio-quiet active galactic nuclei (AGN) or the central regions of radio-loud AGN. We use our results to estimate the $γ$-ray flux from the central regions of nearby AGN, and then to calculate the contribution to the diffuse $γ$-ray flux from unresolved AGN.

astro-ph↗