50 research outputs found
Evidences for two Gamma-Ray Burst afterglow emission regimes
We applied cosmological and absorption corrections to the X-ray and optical
afterglow fluxes of a sample of Gamma-Ray Burst sources of known distance. We
find a good correlation in X-rays and that the GRBs in our sample form two well
defined classes. We tentatively interpret them as radiative and adiabatic
afterglow behaviours in the framework of the fireball model for GRBs. We do not
observe this correlation at optical wavelengths. This discrepancy with the
model may be due to the absorption in the source vicinity.Comment: 4 pages, 2 figures, letter to be published in Astronomy and
Astrophysic
Simultaneous event detection rates by electromagnetic and gravitational wave detectors in the Advanced Era of LIGO and Virgo
We present several estimates of the rate of simultaneous detection of the
merging of a binary system of neutron stars in the electromagnetic and the
gravitational wave domains, assuming that they produce short GRBs. We have
based our estimations on a carefully selected sample of short gamma-ray bursts,
corrected from redshift effects. The results presented in this paper are based
on actual observation only. In the electromagnetic spectrum, we considered
observations by current (Swift and Fermi}) and future (LOFT and SVOM) missions.
In the gravitational wave domain, we consider detections by the Advanced Virgo
instrument alone and the network of both Advanced LIGO and Advanced Virgo. We
discuss on the possible biases present in our sample, and how to fix them. For
present missions, assuming a detection in the following years, we find that we
should observe simultaneously between 0.11 and 4.2 gravitational wave events
per year with Swift} and Fermi} respectively. For future projects (LOFT and
SVOM) we can expect less than one common detection per year. We check the
consistency of our results with several previously published rate of detection
of gravitational waves.Comment: 7 pages, accepted for publication in MNRAS, with note added in proof
correcting the rates for Fermi/SVOM experiment. Added tables 5 and 6 that are
corrected and replace tables 2 and
Simultaneous detection rates of binary neutron star systems in advanced Virgo/LIGO and GRB detectors
The coalescence of two compact objects is a key target for the new
gravitational wave observatories such as Advanced-Virgo (AdV), Advanced-LIGO
(aLIGO) and KAGRA. This phenomenon can lead to the simultaneous detection of
electromagnetic waves in the form of short GRBs (sGRBs) and gravitational wave
transients. This will potentially allow for the first time access to the
fireball and the central engine properties. We present an estimation of the
detection rate of such events, seen both by a Swift-like satellite and
AdV/ALIGO. This rate is derived only from the observations of sGRBs. We show
that this rate, if not very high, predicts a few triggers during the whole life
time of Advanced LIGO-Virgo. We discuss how to increase it using some dedicated
observational strategies. We apply our results to other missions such as the
SVOM French-Chinese satellite project or LOFT.Comment: 7 pages, 1 figure, 7th Huntsville Gamma-Ray Burst Symposium, GRB
2013: paper 18 in eConf Proceedings C130414
Are Ultra-long Gamma-Ray Bursts different?
The discovery of a number of gamma-ray bursts with duration exceeding 1,000
seconds, in particular the exceptional case of GRB 111209A with a duration of
about 25,000 seconds, has opened the question on whether these bursts form a
new class of sources, the so called {\em ultra-long} GRBs, or if they are
rather the tail of the distribution of the standard long GRB duration. In this
Letter, using the long GRB sample detected by {\em Swift}, we investigate on
the statistical properties of ultra-long GRBs and compare them with the overall
long burst population. We discuss also on the differences observed in their
spectral properties. We find that ultra-long GRBs are statistically different
from the standard long GRBs with typical burst duration less than 100-500
seconds, for which a Wolf Rayet star progenitor is usually invoked. We
interpret this result as an indication that an alternative scenario has to be
found in order to explain the ultra-long GRB extreme energetics, as well as the
mass reservoir and its size that can feed the central engine for such a long
time.Comment: 6 pages, submitted to ApJ, minor typo
Discovery of a quiescent neutron star binary in the globular cluster M13
We have discovered with XMM-Newton an X-ray source in the core of the
globular cluster M13, whose X-ray spectral properties suggest that it is a
quiescent neutron star X-ray binary. The spectrum can be well fitted with a
pure hydrogen atmosphere model, with T=76 +/- 3 eV, R=12.8 +/- 0.4 km and an
X-ray luminosity of 7.3 +/- 0.6 x 10^{32} erg/s. In the light of this result,
we have discovered a strong correlation between the stellar encounter rate and
the number of quiescent neutron stars found in the ten globular clusters
observed so far by either XMM-Newton or Chandra. This result lends strong
support to the idea that these systems are primarily produced by stellar
encounters in the core of globular clusters.Comment: 4 pages, 2 B&W figures and 1 color figure. Accepted for publication
in A&A Letters. Revised reference list and minor correction
The Swift Gamma-Ray Burst redshift distribution: selection biases and optical brightness evolution at high-z?
We employ realistic constraints on astrophysical and instrumental selection
effects to model the Gamma-Ray Burst (GRB) redshift distribution using {\it
Swift} triggered redshift samples acquired from optical afterglows (OA) and the
TOUGH survey. Models for the Malmquist bias, redshift desert, and the fraction
of afterglows missing because of host galaxy dust extinction, are used to show
how the "true" GRB redshift distribution is distorted to its presently observed
biased distribution. We also investigate another selection effect arising from
a correlation between and . The analysis, which
accounts for the missing fraction of redshifts in the two data subsets, shows
that a combination of selection effects (both instrumental and astrophysical)
can describe the observed GRB redshift distribution. Furthermore, the observed
distribution is compatible with a GRB rate evolution that tracks the global
SFR, although the rate at high- cannot be constrained with confidence.
Taking selection effects into account, it is not necessary to invoke
high-energy GRB luminosity evolution with redshift to explain the observed GRB
rate at high-.Comment: Version 2. Includes new data, figures and refined analysi
Constraints on the baryonic load of gamma-ray bursts using ultra-high energy cosmic rays
Ultra-high energy cosmic rays are the most extreme energetic particles
detected on Earth, however, their acceleration sites are still mysterious. We
explore the contribution of low-luminosity gamma-ray bursts to the ultra-high
energy cosmic ray flux, since they form the bulk of the nearby population. We
analyse a representative sample of these bursts detected by BeppoSAX, INTEGRAL
and Swift between 1998-2016, and find they can produce a theoretical cosmic ray
flux on Earth of at least particles
km century mol. No suppression mechanisms can reconcile
this value with the flux observed on Earth. Instead, we propose that the jet of
low-luminosity gamma-ray bursts propels only the circumburst medium - which is
accelerated to relativistic speeds - not the stellar matter. This has
implications for the baryonic load of the jet: it should be negligible compared
to the leptonic content.Comment: 5 pages, submitted to MNRA