Angular Dependence of Jitter Radiation Spectra from Small-Scale Magnetic Turbulence

Jitter radiation is produced by relativistic electrons moving in turbulent small-scale magnetic fields such as those produced by streaming Weibel-type instabilities at collisionless shocks in weakly magnetized media. Here we present a comprehensive study of the dependence of the jitter radiation spectra on the properties of, in general, anisotropic magnetic turbulence. We have obtained that the radiation spectra do reflect, to some extent, properties of the magnetic field spatial distribution, yet the radiation field is anisotropic and sensitive to the viewing direction with respect to the field anisotropy direction. We explore the parameter space of the magnetic field distribution and its effect on the radiation spectrum. Some important results include: the presence of the harder-than-synchrotron segment below the peak frequency at some viewing angles, the presence of the high-frequency power-law tail even for a monoenergetic distribution of electrons, the dependence of the peak frequency on the field correlation length rather than the field strength, the strong correlation of the spectral parameters with the viewing angle. In general, we have found that even relatively minor changes in the magnetic field properties can produce very significant effects upon the jitter radiation spectra. We consider these results to be important for accurate interpretation of prompt gamma-ray burst spectra and possibly other sources.Comment: 75 pages, 29 figures, submitted to Ap

Modeling Spectral Variability of Prompt GRB Emission within the Jitter Radiation Paradigm

The origin of rapid spectral variability and certain spectral correlations of the prompt gamma-ray burst emission remains an intriguing question. The recently proposed theoretical model of the prompt emission is build upon unique spectral properties of jitter radiation -- the radiation from small-scale magnetic fields generated at a site of strong energy release (e.g., a relativistic collisionless shock in baryonic or pair-dominated ejecta, or a reconnection site in a magnetically-dominated outflow). Here we present the results of implementation of the model. We show that anisotropy of the jitter radiation pattern and relativistic shell kinematics altogether produce effects commonly observed in time-resolved spectra of the prompt emission, e.g., the softening of the spectrum below the peak energy within individual pulses in the prompt light-curve, the so-called "tracking" behavior (correlation of the observed flux with other spectral parameters), the emergence of hard, synchrotron-violating spectra at the beginning of individual spikes. Several observational predictions of the model are discussed.Comment: ApJL, in pres