74 research outputs found
Dynamical Model of an Expanding Shell
Expanding blast waves are ubiquitous in many astronomical sources, such as
supernovae remnants (SNRs), X-ray emitting binaries (XRBs) and gamma-ray bursts
(GRBs). I consider here the dynamics of such an expanding blast wave, both in
the adiabatic and the radiative regimes. As the blast wave collects material
from the surrounding, it decelerates. A full description of the temporal
evolution of the blast wave requires consideration of both the energy density
and the pressure of the shocked material. The obtained equation is different
than earlier works in which only the energy was considered. The solution
converges to the familiar results in both the ultra-relativistic and the
sub-relativistic (Newtonian) regimes.Comment: Minor revision. Some points clarified, references added. Accepted for
publication in Ap.J. (Lett.
Radiative Mechanisms in GRB prompt emission
Motivated by the Fermi gamma-ray space telescope results, in recent years
immense efforts were given to understanding the mechanism that leads to the
prompt emission observed. The failure of the optically thin emission models
(synchrotron and synchrotron self Compton) increased interest in alternative
models. Optically thick models, while having several advantages, also face
difficulty in capturing several key observables. Theoretical efforts are
focused in two main directions: (1) mechanisms that act to broaden the Planck
spectrum; and (2) combining the optically thin and optically thick models to a
hybrid model that could explain the key observables.Comment: 9 pages, 2 figures, 1 table; Invited review, to appear in the
proceedings of the Gamma-Ray Burst Symposium 2012- IAA-CSIC - Marbella,
editors: Castro-Tirado, A. J., Gorosabel, J. and Park, I.
Constraining Magnetization of Gamma-Ray Bursts Outflows using Prompt Emission Fluence
I consider here acceleration and heating of relativistic outflow by local
magnetic energy dissipation process in Poynting flux dominated outflow.
Adopting the standard assumption that the reconnection rate scales with the
Alfven speed, I show here that the fraction of energy dissipated as thermal
photons cannot exceed (13 % (for adiabatic index
) of the kinetic energy at the photosphere. Even in the most
radiatively efficient scenario, the energy released as non-thermal photons
during the prompt phase is at most equal to the kinetic energy of the outflow.
These results imply that calorimetry of the kinetic energy that can be done
during the afterglow phase, could be used to constrain the magnetization of
gamma-ray bursts (GRB) outflows. I discuss the recent observational status, and
its implications on constraining the magnetization in GRB outflows.Comment: (Very) extensive discussions about current observational constraints,
implications and limitations. Accepted for publication in the Astrophysical
Journa
Plasmas in Gamma-Ray Bursts: particle acceleration, magnetic fields, radiative Processes and environments
Being the most extreme explosions in the universe, gamma-ray bursts (GRBs)
provide a unique laboratory to study various plasma physics phenomena. The
complex lightcurve and broad-band, non-thermal spectra indicate a very
complicated system on the one hand, but on the other hand provide a wealth of
information to study it. In this chapter I focus on recent progress in some of
the key unsolved physical problems. These include: (1) Particle acceleration
and magnetic field generation in shock waves; (2) Possible role of strong
magnetic fields in accelerating the plasmas, and accelerating particles via
magnetic reconnection process; (3) Various radiative processes that shape the
observed lightcurve and spectra, both during the prompt and the afterglow
phases, and finally (4) GRB environments and their possible observational
signature.Comment: Invited chapter for a special issue of "galaxies", dedicated to
"Cosmic Plasmas and Electromagnetic phenomena
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