1,133 research outputs found
Detection of a very bright optical flare from a gamma-ray burst at redshift 6.29
In this letter we discuss the flux and the behavior of the bright optical
flare emission detected by the 25 cm TAROT robotic telescope during the prompt
high-energy emission and the early afterglow. We combine our data with
simultaneous observations performed in X-rays and we analyze the broad-band
spectrum. These observations lead us to emphasize the similarity of GRB 050904
with GRB 990123, a remarkable gamma-ray burst whose optical emission reached
9th magnitude. While GRB 990123 was, until now, considered as a unique event,
this observation suggests the existence of a population of GRBs which have very
large isotropic equivalent energies and extremely bright optical counterparts.
The luminosity of these GRBs is such that they are easily detectable through
the entire universe. Since we can detect them to very high redshift even with
small aperture telescopes like TAROT, they will constitute powerful tools for
the exploration of the high-redshift Universe and might be used to probe the
first generation of stars.Comment: 9 pages, 3 figures. Accepted in ApJ
Fall back accretion and energy injections in gamma-ray bursts
Intense flares that occur at late times relative to the prompt phase have
been observed by the satellite in the X-ray afterglows of gamma-ray
bursts (GRBs). Here, we present a detailed analysis on the fall back accretion
process to explain the intense flare phase in the very early X-ray afterglow
light curves. To reproduce the afterglow at late times, we resort to the
external shock by engaging energy injections. By applying our model to GRBs
080810, 081028 and 091029, we show that their X-ray afterglow light curves can
be reproduced well. We then apply our model to the ultra-long GRB
111209A, which is the longest burst ever observed. The very early X-ray
afterglow of GRB 111209A showed many interesting features, such as a
significant bump observed at around 2000 s after the /BAT trigger. We
assume two constant energy injection processes in our model. These can explain
the observed plateau at X-ray wavelength in the relatively early stage
( s) and a second X-ray plateau and optical rebrightening at
about s. Our analysis supports the scenario that a significant amount
of material may fall back toward the central engine after the prompt phase,
causing an enhanced and long lived mass accretion rate powering a
Poynting-flux-dominated outflow.Comment: 2 tables, 3 figures, accepted by MNRA
GW170817: implications for the local kilonova rate and for surveys from ground-based facilities
We compute the local rate of events similar to GRB 170817A, which has been
recently found to be associated with a kilonova (KN) outburst. Our analysis
finds an observed rate of such events of R
Gpcyr. After comparing at their face values this density of sGRB
outbursts with the much higher density of Binary Neutron Star (BNS) mergers of
1540 Gpcyr, estimated by LIGO-Virgo
collaboration, one can conclude, admittedly with large uncertainty that either
only a minor fraction of BNS mergers produces sGRB/KN events or the sGRBs
associated with BNS mergers are beamed and observable under viewing angles as
large as . Finally we provide preliminary estimates
of the number of sGRB/KN events detected by future surveys carried out with
present/future ground-based/space facilities, such as LSST, VST, ZTF, SKA and
THESEUS.Comment: MNRAS accepted, 6 pages, 1 figur
The ultra-long GRB 111209A - II. Prompt to afterglow and afterglow properties
The "ultra-long" Gamma Ray Burst GRB 111209A at redshift z=0.677, is so far
the longest GRB ever observed, with rest frame prompt emission duration of ~4
hours. In order to explain the bursts exceptional longevity, a low metallicity
blue supergiant progenitor has been invoked. In this work, we further
investigate this peculiar burst by performing a multi-band temporal and
spectral analysis of both the prompt and the afterglow emission. We use
proprietary and publicly available data from Swift, Konus Wind, XMM-Newton,
TAROT as well as from other ground based optical and radio telescopes. We find
some peculiar properties that are possibly connected to the exceptional nature
of this burst, namely: i) an unprecedented large optical delay of 410+/-50 s is
measured between the peak epochs of a marked flare observed also in gamma-rays
after about 2 ks from the first Swift/BAT trigger; ii) if the optical and
X-ray/gamma-ray photons during the prompt emission share a common origin, as
suggested by their similar temporal behavior, a certain amount of dust in the
circumburst environment should be introduced, with rest frame visual dust
extinction of AV=0.3-1.5 mag; iii) at the end of the X-ray "steep decay phase"
and before the start of the X-ray afterglow, we detect the presence of a hard
spectral extra power law component never revealed so far. On the contrary, the
optical afterglow since the end of the prompt emission shows more common
properties, with a flux power law decay with index alpha=1.6+/-0.1 and a late
re-brightening feature at 1.1 day. We discuss our findings in the context of
several possible interpretations given so far to the complex multi-band GRB
phenomenology. We also attempt to exploit our results to further constrain the
progenitor nature properties of this exceptionally long GRB, suggesting a
binary channel formation for the proposed blue supergiant progenitor.Comment: ApJ accepted. Revised version with substantial adjustments, the main
results remain unchange
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