2,845 research outputs found
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
saprEMo: a simplified algorithm for predicting detections of electromagnetic transients in surveys
The multi-wavelength detection of GW170817 has inaugurated multi-messenger
astronomy. The next step consists in interpreting observations coming from
population of gravitational wave sources. We introduce saprEMo, a tool aimed at
predicting the number of electromagnetic signals characterised by a specific
light curve and spectrum, expected in a particular sky survey. By looking at
past surveys, saprEMo allows us to constrain models of electromagnetic emission
or event rates. Applying saprEMo to proposed astronomical missions/observing
campaigns provides a perspective on their scientific impact and tests the
effect of adopting different observational strategies. For our first case
study, we adopt a model of spindown-powered X-ray emission predicted for a
binary neutron star merger producing a long-lived neutron star. We apply
saprEMo on data collected by XMM-Newton and Chandra and during s of
observations with the mission concept THESEUS. We demonstrate that our emission
model and binary neutron star merger rate imply the presence of some signals in
the XMM-Newton catalogs. We also show that the new class of X-ray transients
found by Bauer et al. in the Chandra Deep Field-South is marginally consistent
with the expected rate. Finally, by studying the mission concept THESEUS, we
demonstrate the substantial impact of a much larger field of view in searches
of X-ray transients
Extinction properties of the X-ray bright/optically faint afterglow of GRB 020405
We present an optical-to-X-ray spectral analysis of the afterglow of GRB
020405. The optical spectral energy distribution not corrected for the
extragalactic extinction is significantly below the X-ray extrapolation of the
single powerlaw spectral model suggested by multiwavelength studies. We
investigate whether considerable extinction could explain the observed spectral
``mismatch'' by testing several types of extinction curves. For the first time
we test extinction curves computed with time-dependent numerical simulations of
dust grains destruction by the burst radiation. We find that an extinction law
weakly depen dent on wavelength can reconcile the unabsorbed optical and X-ray
data with the expected synchrotron spectrum. A gray extinction law can be
provided by a dust grain size distribution biased toward large grains.Comment: 6 pages, 5 figures, accepted for publication on A&
- …