Synchrotron radiation

About: Synchrotron radiation is a research topic. Over the lifetime, 14639 publications have been published within this topic receiving 244775 citations. The topic is also known as: magnetobremsstrahlung radiation & Synchrotron Radiation.

The multifrequency variability of Mrk 421

Abstract: We present a model of the multifrequency variability of the blazar Mrk 421. The model explains correlated variability observed from Very High Energy (VHE) gamma rays to radio frequencies. We assume that the dominant part of the stationary emission from the radio frequencies to the X-rays is generated by the synchrotron radiation of relativistic electrons ejected from the central engine. The particles move from the center of the source with relativistic velocities and form an inhomogeneous jet. We perform detailed calculations of the radiation transfer and calculate evolution of the electron energy spectrum along the jet. We explain the observed variability by the evolving synchrotron and Inverse-Compton (IC) radiation of a compact component (a blob) which travels along the jet. Two scenarios have been considered as mechanisms to generate VHE flares. The first scenario assumes that the high energy electrons, necessary for generation of the VHE flares, are injected into the jet, directly from the central engine or from an acceleration zone (e.g., a shock wave). The second scheme assumes that the high energy electrons are generated in situ by acceleration, for example by diffusive shock waves or a localized turbulence inside the jet. The particles evolve along the jet. They are cooled by the radiative processes and by the adiabatic expansion which compete with the acceleration process and the injection of high energy electrons. We present new observations we obtained in the radio domain for Mrk 421. The radio data gathered in February–April 2001 show a well defined radio outburst which corresponds to an X-ray outburst observed by RXTE-ASM and a gamma-ray flare detected by HEGRA in the TeV range. The best of our knowledge, this is the first direct observational evidence for a flare observed simultaneously in the radio range and at very high energies. Our scenario with acceleration of electrons in the middle part of the jet describes well the temporal evolution of such multispectral flare.

Spectral and temporal signatures of ultrarelativistic protons in compact sources

Abstract: We present calculations of the spectral and temporal radiative signatures expected from ultrarelativistic protons in compact sources. The coupling between the protons and the leptonic component is assumed to occur via Bethe-Heitler pair production. This process is treated by modeling the results of Monte-Carlo simulations and incorporating them in a time-dependent kinetic equation, that we subsequently solve numerically. Thus, the present work is, in many respects, an extension of the leptonic `one-zone' models to include hadrons. Several examples of astrophysical importance are presented, such as the signature resulting from the cooling of relativistic protons on an external black-body field and that of their cooling in the presence of radiation from injected electrons. We also investigate and refine the threshold conditions for the 'Pair Production/Synchrotron' feedback loop which operates when relativistic protons cool efficiently on the synchrotron radiation of the internally produced Bethe-Heitler pairs. We demonstrate that an additional component of injected electrons lowers the threshold for this instability.

Stochastic Acceleration and Photon Emission in Electron-dominated Solar Flares

Abstract: We examine four electron-dominated flares, two from the GRS instrument on 1989 March 6, and two from the EGRET and BATSE instruments on 1991 June 30 and 1991 July 2. Their photon spectra, which are almost all caused by electron bremsstrahlung radiation, show significant deviations from a simple power-law form. These are attributed to the deviations in the spectra of the accelerated electrons. We develop three stochastic acceleration models to explain the shape of the photon spectra: the hard sphere model, the whistler wave model, and a more general, but still simplified, stochastic acceleration model. For photon emissions, we use a simple sum of the thin target emission from the trapped electrons at the acceleration site near the loop top and the thick target emission from the escaping electrons which travel along the magnetic field lines and radiate in the denser chromosphere at the footpoints. We find that the hard sphere model does not fit any of the flares and can be ruled out. The other two models show that the high-energy cutoff in the two GRS flares can be attributed to synchrotron radiation losses in the presence of a 500 G magnetic field at the acceleration site. The observed break in the photon spectra of all four flares around 1 MeV is attributed to a combination of the energy dependence of the escape time of particles out of the acceleration region and the change in the energy dependence of the bremsstrahlung cross section between the nonrelativistic and relativistic regimes. Further steepening of the spectrum at even lower energies is caused by Coulomb losses at the acceleration site. We find that acceleration timescales as low as ~1 s are possible with a ratio of turbulent to the magnetic field energy densities of ~10-4. We also set limits on the plasma density, the size of the acceleration region, and the spectrum of the plasma turbulence.