相关论文: 2nd-order Fermi acceleration as the origin of the …
Recent Fermi results have focused attention on gamma-ray burst's (GRB) prompt emission phase, which is rich in phenomenology and poorly understood. The broad band spectra observed by Fermi does not fit into any of the frameworks of existing…
Supernova remnants (SNRs) have been regarded for many decades as the sources of Galactic cosmic rays (CRs) up to a few PeV. However, only with the advent of Fermi-LAT it has been possible to detect - at least in some SNRs - \gamma-rays…
Relativistic flows resulting from sudden explosive events upscatter ambient interstellar photons of local radiation fields. For Lorentz factor $ > 100$ and dense optical - UV radiation fields the emergent signal is a typical gamma ray…
Many galaxy clusters have giant halos of non-thermal radio emission, indicating the presence of relativistic electrons in the clusters. Relativistic protons may also be accelerated by merger and/or accretion shocks in galaxy clusters. These…
In this study, we treat the Fermi bubbles as a scaled-up version of supernova remnants (SNRs). The bubbles are created through activities of the super-massive black hole (SMBH) or starbursts at the Galactic center (GC). Cosmic-rays (CRs)…
Gamma-ray emission from large structures is useful for tracing the propagation and distribution of cosmic rays throughout our Galaxy. For example, the search for gamma-ray emission from Giant Molecular Clouds may allow us to probe the flux…
The origin of the extended X-ray emission in the large-scale jets of active galactic nuclei (AGNs) poses challenges to conventional models of acceleration and emission. Although the electron synchrotron radiation is considered the most…
Observations of gamma-ray bursts by the Fermi satellite, capable of detecting photons in a very broad energy band: 8keV to >300GeV, have opened a new window for the study of these enigmatic explosions. It is widely assumed that photons of…
The Fermi bubbles are gigantic gamma-ray structures in our Galaxy. The physical origin of the bubbles is still under debate. The leading scenarios can be divided into two categories. One is the nuclear star forming activity similar to…
The Galactic Center's giant outflows are manifest in three different, non-thermal phenomena: i) the hard-spectrum, \gamma-ray `Fermi Bubbles' emanating from the nucleus and extending to |b| ~ 50 degrees; ii) the hard-spectrum,…
It is shown that an ultrarelativistic shock with the Lorentz factor of order of tens or higher propagating in a moderately dense interstellar medium (density above $\sim 1000 $ cm$^{-3}$) undergoes a fast dramatic transformation into a…
New two- and three-dimensional calculations are presented of relativistic jet propagation and break out in massive Wolf-Rayet stars. Such jets are thought responsible for gamma-ray bursts. As it erupts, the jet is surrounded by a cocoon of…
The origin of the pulsed gamma-ray emission in pulsars remains an open issue. The combination of sensitive observations in the GeV domain by AGILE and {\em Fermi}-LAT and increasingly sophisticated numerical simulations have recently…
We perform two distinct spatio-spectral reconstructions of the gamma-ray sky in the range of 0.56-316 GeV based on Fermi Large Area Telescope (LAT) data. Both describe the sky brightness to be composed of a diffuse-emission and a…
We show that the excellent optical and gamma-ray data available for GRB 080319B rule out the internal shock model for the prompt emission. The data instead point to a model in which the observed radiation was produced close to the…
Fast radio bursts (FRBs) are one of the most exciting new mysteries of astrophysics. Their origin is still unknown, but recent observations seems to link them to Soft Gamma Repeaters and, in particular, to magnetar giant flares (MGFs). The…
We describe the theory of Fermi-type acceleration, including first-order Fermi acceleration at a parallel shock front and second-order Fermi acceleration in a test particle limit. Including the theory of the turbulent acceleration and the…
In almost any scenario for 'cosmological' gamma-ray bursts (and in many models where they originate in our own Galaxy), the initial energy density is so large that the resulting relativistic plasma expands with $v\sim c$ producing a blast…
It has been widely accepted that relativistic effects have to be used for modelling the wide classes of events associated with active galactic nuclei and galactic superluminal sources. Here we propose a simple analytical model of…
Photospheric emission may originate from relativistic outflows in two qualitatively different regimes:\ last scattering of photons inside the outflow at the photospheric radius, or radiative diffusion to the boundary of the outflow. In this…