439 research outputs found
Synchrotron and Synchrotron Self-Compton Spectral Signatures and Blazar Emission Models
We find that energy losses due to synchrotron self-Compton (SSC) emission in
blazar jets can produce distinctive signatures in the time-averaged synchrotron
and SSC spectra of these objects. For a fairly broad range of particle
injection distributions, SSC-loss dominated synchrotron emission exhibits a
spectral dependence . The presence or absence of this
dependence in the optical and ultraviolet spectra of flat spectrum radio
quasars such as 3C~279 and in the soft X-ray spectra of high frequency BL Lac
objects such as Mrk 501 gives a robust measure of the importance of SSC losses.
Furthermore, for partially cooled particle distributions, spectral breaks of
varying sizes can appear in the synchrotron and SSC spectra and will be related
to the spectral indices of the emission below the break. These spectral
signatures place constraints on the size scale and the non-thermal particle
content of the emitting plasma as well as the observer orientation relative to
the jet axis.Comment: 4 pages, 1 figure, LaTeX2e, emulateapj5.sty, accepted for publication
in Ap
Angular, spectral, and time distributions of highest energy protons and associated secondary gamma-rays and neutrinos propagating through extragalactic magnetic and radiation fields
The angular, spectral and temporal features of the highest energy protons and
accompanying them secondary neutrinos and synchrotron gamma-rays propagating
through the intergalactic magnetic and radiation fields are studied using the
analytical solutions of the Boltzmann transport equation obtained in the limit
of the small-angle and continuous-energy-loss approximation.Comment: 21 pages, 13 figure
Electron Acceleration and Time Variability of High Energy Emission from Blazars
Blazars are known to emit a broad band emission from radio to gamma-rays with
rapid time variations, particularly, in X- and gamma-rays. Synchrotron
radiation and inverse Compton scattering are thought to play an important role
in emission and the time variations are likely related to the acceleration of
nonthermal electrons. As simultaneous multiwavelength observations with
continuous time spans are recently available, some characteristics of electron
acceleration are possibly inferred from the spectral changes of high energy
emission. In order to make such inferences, we solve the time-dependent kinetic
equations of electrons and photons simultaneously using a simple model for
electron acceleration. We then show how the time variations of emission are
dependent on electron acceleration. We also present a simple model for a flare
in X-rays and TeV gamma-rays by temporarily changing the acceleration
timescale. Our model will be used, in future, to analyze observed data in
detail to obtain information on electron acceleration in blazars.Comment: 24 pages, 12 figures, accepted by the Astrophysical Journa
Synchrotron and SSC Emission and the Blast-Wave Model of Gamma-Ray Bursts
We investigate the dynamics and radiation from a relativistic blast-wave
which decelerates as it sweeps up ambient matter. The bulk kinetic energy of
the blast-wave shell is converted into internal energy by the process of
accreting external matter. If it takes the form of non-thermal electrons and
magnetic fields, then this internal energy will be emitted as synchrotron and
synchrotron self-Compton radiation. We perform analytic and numerical
calculations for the deceleration and radiative processes and present
time-resolved spectra throughout the evolution of the blast-wave. We also
examine the dependence of the burst spectra and light curves on various
parameters describing the magnetic field and non-thermal electron
distributions. We find that for bursts such as GRB~910503, GRB~910601 and
GRB~910814, the spectral shapes of the prompt gamma-ray emission at the peaks
in strongly constrain the magnetic fields in these bursts to be
well below (\la 10^{-2}) the equipartition values. These calculations are
also considered in the context of the afterglow emission from the recently
detected gamma-ray burst counterparts.Comment: 27 pages, 5 figures, submitted to Ap
Spectral Energy Distributions of Gamma Ray Bursts Energized by External Shocks
Sari, Piran, and Narayan have derived analytic formulas to model the spectra
from gamma-ray burst blast waves that are energized by sweeping up material
from the surrounding medium. We extend these expressions to apply to general
radiative regimes and to include the effects of synchrotron self-absorption.
Electron energy losses due to the synchrotron self-Compton process are also
treated in a very approximate way. The calculated spectra are compared with
detailed numerical simulation results. We find that the spectral and temporal
breaks from the detailed numerical simulation are much smoother than the
analytic formulas imply, and that the discrepancies between the analytic and
numerical results are greatest near the breaks and endpoints of the synchrotron
spectra. The expressions are most accurate (within a factor of ~ 3) in the
optical/X-ray regime during the afterglow phase, and are more accurate when
epsilon_e, the fraction of swept-up particle energy that is transferred to the
electrons, is <~ 0.1. The analytic results provide at best order-of-magnitude
accuracy in the self-absorbed radio/infrared regime, and give poor fits to the
self-Compton spectra due to complications from Klein-Nishina effects and
photon-photon opacity.Comment: 16 pages, 7 figures, ApJ, in press, 537, July 1, 2000. Minor changes
in response to referee report, corrected figure
Energetics of Tev Blazars and Physical Constraints on their Emission Regions
Using multi-frequency spectra from TeV blazars in quiescent states, we obtain
the physical parameters of the emission region of blazars within the framework
of the one-zone synchrotron self-Compton (SSC) model. We numerically calculate
the steady-state energy spectra of electrons by self-consistently taking into
account the effects of radiative cooling with a proper account of the
Klein-Nishina effects. Here electrons are assumed to be injected with a
power-law spectrum and to escape on a finite time scale, which naturally leads
to the existence of a break energy scale. Although we do not use time
variabilities but utilize a model of electron escape to constrain the size of
the emission region, the resultant size turns out to be similar to that
obtained based on time variabilities. Through detailed comparison of the
predicted emission spectra with observations, we find that for Mrk 421, Mrk
501, and PKS 2155--304, the energy density of relativistic electrons is about
an order of magnitude larger than that of magnetic fields with an uncertainty
within a factor of a few.Comment: Accepted for publication in Ap
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