25,894 research outputs found
A two component jet model for the X-ray afterglow flat segment in short GRB 051221A
In the double neutron star merger or neutron star-black hole merger model for
short GRBs, the outflow launched might be mildly magnetized and neutron rich.
The magnetized neutron-rich outflow will be accelerated by the magnetic and
thermal pressure and may form a two component jet finally, as suggested by
Vlahakis, Peng & K\"{o}nigl (2003). We show in this work that such a two
component jet model could well reproduce the multi-wavelength afterglow
lightcurves, in particular the X-ray flat segment, of short GRB 051221A. In
this model, the central engine need not to be active much longer than the
prompt ray emission.Comment: 11 pages, 2 figure; Accepted for publication by ApJ
Cross correlations of Frank sequences and Chu Sequences.
Sets of Frank sequences and Chu sequences are two classes of polyphase sequence with ideal periodic autocorrelation functions, which at the same time have optimum crosscorrelation functions. The authors consider the crosscorrelations of sets of combined Frank/Chu sequences, which contain a larger number of sequences than either of the two constituent sets. It is shown analytically that the crosscorrelations are similar to those of the original sets with one exception, while the autocorrelations remain perfectly impulsiv
Behavior of X-Ray Dust Scattering and Implications for X-Ray Afterglows of Gamma-Ray Bursts
The afterglows of gamma-ray bursts (GRBs) have commonly been assumed to be
due to shocks sweeping up the circum-stellar medium. However, most GRBs have
been found in dense star-forming regions where a significant fraction of the
prompt X-ray emission can be scattered by dust grains. Here we revisit the
behavior of dust scattering of X-rays in GRBs. We find that the features of
some X-ray afterglows from minutes to days after the gamma-ray triggers are
consistent with the scattering of prompt X-ray emission from GRBs off host dust
grains. This implies that some of the observed X-ray afterglows (especially
those without sharp rising and decaying flares) could be understood with a
dust-scattering--driven emission model.Comment: ApJ, in pres
The X-ray afterglow of GRB 081109A: clue to the wind bubble structure
We present the prompt BAT and afterglow XRT data of Swift-discovered
GRB081109A up to ~ 5\times 10^5 sec after the trigger, and the early
ground-based optical follow-ups. The temporal and spectral indices of the X-ray
afterglow emission change remarkably. We interpret this as the GRB jet first
traversing the freely expanding supersonic stellar wind of the progenitor with
density varying as . Then after approximately 300 sec the
jet traverses into a region of apparent constant density similar to that
expected in the stalled-wind region of a stellar wind bubble or the
interstellar medium (ISM). The optical afterglow data are generally consistent
with such a scenario. Our best numerical model has a wind density parameter
{, a density of the stalled wind ,
and a transition radius cm}. Such a transition
radius is smaller than that predicted by numerical simulations of the stellar
wind bubbles and may be due to a rapidly evolving wind of the progenitor close
to the time of its core-collapse.Comment: 7 pages, 5 figures, 2 tables, MNRAS accepted for publicatio
Neutrino emission from a GRB afterglow shock during an inner supernova shock breakout
The observations of a nearby low-luminosity gamma-ray burst (GRB) 060218
associated with supernova SN 2006aj may imply an interesting astronomical
picture where a supernova shock breakout locates behind a relativistic GRB jet.
Based on this picture, we study neutrino emission for early afterglows of GRB
060218-like GRBs, where neutrinos are expected to be produced from photopion
interactions in a GRB blast wave that propagates into a dense wind.
Relativistic protons for the interactions are accelerated by an external shock,
while target photons are basically provided by the incoming thermal emission
from the shock breakout and its inverse-Compton scattered component. Because of
a high estimated event rate of low-luminosity GRBs, we would have more
opportunities to detect afterglow neutrinos from a single nearby GRB event of
this type by IceCube. Such a possible detection could provide evidence for the
picture described above.Comment: 6 pages, 2 figures, accepted for publication in MNRA
GeV-TeV and X-ray flares from gamma-ray bursts
The recent detection of delayed X-ray flares during the afterglow phase of
gamma-ray bursts (GRBs) suggests an inner-engine origin, at radii inside the
deceleration radius characterizing the beginning of the forward shock afterglow
emission. Given the observed temporal overlapping between the flares and
afterglows, there must be inverse Compton (IC) emission arising from such flare
photons scattered by forward shock afterglow electrons. We find that this IC
emission produces GeV-TeV flares, which may be detected by GLAST and
ground-based TeV telescopes. We speculate that this kind of emission may
already have been detected by EGRET from a very strong burst--GRB940217. The
enhanced cooling of the forward shock electrons by the X-ray flare photons may
suppress the synchrotron emission of the afterglows during the flare period.
The detection of GeV-TeV flares combined with low energy observations may help
to constrain the poorly known magnetic field in afterglow shocks. We also
consider the self-IC emission in the context of internal-shock and
external-shock models for X-ray flares. The emission above GeV from internal
shocks is low, while the external shock model can also produce GeV-TeV flares,
but with a different temporal behavior from that caused by IC scattering of
flare photons by afterglow electrons. This suggests a useful approach for
distinguishing whether X-ray flares originate from late central engine activity
or from external shocks.Comment: slightly shortened version, accepted for publication in ApJ Letters,
4 emulateapj pages, no figure
High Energy Neutrino Flashes from Far-Ultraviolet and X-ray Flares in Gamma-Ray Bursts
The recent observations of bright optical and x-ray flares by the Swift
satellite suggest these are produced by the late activities of the central
engine. We study the neutrino emission from far-ultraviolet and x-ray flares
under the late internal shock model. We show that the efficiency of pion
production in the highest energy is comparable to or higher than the unity, and
the contribution from such neutrino flashes to a diffuse very high energy
neutrino background can be larger than that of prompt bursts if the total
baryonic energy input into flares is comparable to the radiated energy of
prompt bursts. These signals may be detected by IceCube and are very important
because they have possibilities to probe the nature of flares (the baryon
loading, the photon field, the magnetic field and so on).Comment: 4 pages, 3 figures, version published in PR
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