Related papers: A Testable the Stochastic Acceleration Model for F…
We present the highly significant detection of a quasi-periodic flux modulation with a period of 22.2 min seen in the X-ray data of the Sgr A* flare of 2004 August 31. This flaring event, which lasted a total of about three hours, was…
We investigate rapid TeV flaring in markarian 501 in the frame of a time-dependent one-zone synchrotron self-Compton (SSC) model. Inthis model, electrons are accelerated to extra-relativistic energy through the stochastic particle…
Using 2D particle-in-cell (PIC) plasma simulations we study electron acceleration by temperature anisotropy instabilities, assuming conditions typical of above-the-loop-top (ALT) sources in solar flares. We focus on the long-term effect of…
The very short and bright flare of 3C 279 detected with {\it Fermi}-LAT in 2013 December is tested by a model with stochastic electron acceleration by turbulences. Our time-dependent simulation shows that the very hard spectrum and…
Adopting the hypothesis that the nonthermal emission of Active Galactic Nuclei (AGN) is primarily due to the acceleration of protons, we construct a simple model in which the interplay of acceleration and losses can be studied together with…
We report the detection of emission from a non-thermal electron distribution in a small solar microflare (GOES class A5.7) observed by the Nuclear Spectroscopic Telescope Array (NuSTAR), with supporting observation by the Reuven Ramaty High…
We briefly review the theory of gamma ray production in solar flares and present the highlights of the observations and their implications. Specifically: (i) the gamma ray data show that a large fraction of the released flare energy is in…
Recently the AGILE and Fermi/LAT detectors uncovered giant $\gamma$-ray flares from the Crab nebula. The duration of these flares is a few days. The Fermi/LAT data with monthly time binning further showed significant variability of the…
The detection of a mm/Sub-mm ``bump'' in Sgr A*'s radio spectrum suggests that at least a portion of its overall emission is produced within a compact accretion torus. This inference is strengthened by observations of strong linear…
The high energy emission of microquasars is thought to originate from high energy particles. Depending on the spectral state, the distribution of these particles can be thermal with a high temperature (typically 100 keV) or non-thermal and…
The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows to obtain unique information about primary energy release mechanisms in solar flares. The SSRT spatially resolved images and a high…
We present 3D general relativistic magnetohydrodynamic (GRMHD) simulations of the accretion flow surrounding Sagittarius A* that are initialized using larger-scale MHD simulations of the $\sim$ 30 Wolf--Rayet (WR) stellar winds in the…
RHESSI measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized. RHESSI's precise measurements of hard X-ray continuum spectra enable model-independent deconvolution to obtain…
The recent detection of polarized radiation from Sgr A* requires a non-thermal electron distribution for the emitting plasma. The Faraday rotation measure must be small, placing strong limits on the density and magnetic field strength. We…
We study the acceleration, transport, and emission of particles in relativistic jets. Localized stochastic particle acceleration, spatial diffusion, and synchrotron as well as synchrotron self-Compton emission are considered in a leptonic…
Radio and mm-wavelength observations of Sagittarius A* (Sgr A*), the radio source associated with the supermassive black hole at the center of our Galaxy, show that it behaves as a partially self-absorbed synchrotron-emitting source. The…
We report on the presence of very rapid hard X-ray variability in the $\gamma$-ray binary LS I +61 303. The results were obtained by analysing NuSTAR data, which show two achromatic strong flares on ks time-scales before apastron. The…
We study the magnetic Rayleigh-Taylor instability in relativistic collisionless plasma, as an astrophysical process for nonthermal particle acceleration. We consider dense plasma on top of a highly magnetized cavity with sheared magnetic…
Accreting black holes produce powerful relativistic plasma jets which emit radiation across all observable wavelengths but the details of the initial acceleration and confinement of the jet are uncertain. We apply an innovative new model…
The necessity for compact table-top x-ray sources with higher brightness, shorter wavelength and shorter pulse duration has led to the development of complementary sources based on laser-plasma accelerators, in contrast to conventional…