6,870 research outputs found
A Complete Reference of the Analytical Synchrotron External Shock Models of Gamma-Ray Bursts
Gamma-ray bursts are most luminous explosions in the universe. Their ejecta
are believed to move towards Earth with a relativistic speed. The interaction
between this "relativistic jet" and a circum burst medium drives a pair of
(forward and reverse) shocks. The electrons accelerated in these shocks radiate
synchrotron emission to power the broad-band afterglow of GRBs. The external
shock theory is an elegant theory, since it invokes a limit number of model
parameters, and has well predicted spectral and temporal properties. On the
other hand, depending on many factors (e.g. the energy content, ambient density
profile, collimation of the ejecta, forward vs. reverse shock dynamics, and
synchrotron spectral regimes), there is a wide variety of the models. These
models have distinct predictions on the afterglow decaying indices, the
spectral indices, and the relations between them (the so-called "closure
relations"), which have been widely used to interpret the rich multi-wavelength
afterglow observations. This review article provides a complete reference of
all the analytical synchrotron external shock afterglow models by deriving the
temporal and spectral indices of all the models in all spectral regimes,
including some regimes that have not been published before. The review article
is designated to serve as a useful tool for afterglow observers to quickly
identify relevant models to interpret their data. The limitations of the
analytical models are reviewed, with a list of situations summarized when
numerical treatments are needed.Comment: 119 pages, 45 figures, invited review accepted for publication in New
Astronomy Review
The extension of variability properties in gamma-ray bursts to blazars
Both gamma-ray bursts (GRBs) and blazars have relativistic jets pointing at a
small angle from our line of sight. Several recent studies suggested that these
two kinds of sources may share similar jet physics. In this work, we explore
the variability properties for GRBs and blazars as a whole. We find that the
correlation between minimum variability timescale (MTS) and Lorentz factor,
, as found only in GRBs by Sonbas et al. can be extended to blazars
with a joint correlation of . The same
applies to the correlation as
found in GRBs, which can be well extended into blazars as well. These results
provide further evidence that the jets in these two kinds of sources are
similar despite of the very different mass scale of their central engines.
Further investigations of the physical origin of these correlations are needed,
which can shed light on the nature of the jet physics.Comment: 6 pages, 2 figures, accepted for publication in MNRA
A feedback-driven bubble G24.136+00.436: a possible site of triggered star formation
We present a multi-wavelength study of the IR bubble G24.136+00.436. The
J=1-0 observations of CO, CO and CO were carried out with
the Purple Mountain Observatory 13.7 m telescope. Molecular gas with a velocity
of 94.8 km s is found prominently in the southeast of the bubble,
shaping as a shell with a total mass of . It is
likely assembled during the expansion of the bubble. The expanding shell
consists of six dense cores. Their dense (a few of cm) and
massive (a few of ) characteristics coupled with the broad
linewidths ( 2.5 km s) suggest they are promising sites of forming
high-mass stars or clusters. This could be further consolidated by the
detection of compact HII regions in Cores A and E. We tentatively identified
and classified 63 candidate YSOs based on the \emph{Spitzer} and UKIDSS data.
They are found to be dominantly distributed in regions with strong emission of
molecular gas, indicative of active star formation especially in the shell. The
HII region inside the bubble is mainly ionized by a O8V star(s), of the
dynamical age 1.6 Myr. The enhanced number of candidate YSOs and
secondary star formation in the shell as well as time scales involved, indicate
a possible scenario of triggering star formation, signified by the "collect and
collapse" process.Comment: 13 pages, 10 figures, 4 tables, accepted by Ap
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