325 research outputs found
Average power density spectrum of long GRBs detected with BeppoSAX/GRBM and with Fermi/GBM
From past experiments the average power density spectrum (PDS) of GRBs with
unknown redshift was found to be modelled from 0.01 to 1 Hz with a power-law,
f^(-alpha), with alpha broadly consistent with 5/3. Recent analyses of the
Swift/BAT catalogue showed analogous results in the 15-150 keV band. We carried
out the same analysis on the bright GRBs detected by BeppoSAX/GRBM and
Fermi/GBM. The BeppoSAX/GRBM data, in the energy range 40-700 keV and with 7.8
and 0.5-ms time resolutions, allowed us to explore for the first time the
average PDS at very high frequencies (up to 1 kHz) and reveal a break around
1-2 Hz, previously found in CGRO/BATSE data. The Fermi/GBM data, in the energy
band 8-1000 keV, allowed us to explore for the first time the average PDS
within a broad energy range. Our results confirm and extend the energy
dependence of the PDS slope, according to which harder photons have shallower
PDS.Comment: 13 pages, 9 figures, accepted to MNRA
A search for pulsations in short gamma-ray bursts to constrain their progenitors
We searched for periodic and quasiperiodic signal in the prompt emission of a
sample of 44 bright short gamma-ray bursts detected with Fermi/GBM, Swift/BAT,
and CGRO/BATSE. The aim was to look for the observational signature of
quasiperiodic jet precession which is expected from black hole-neutron star
mergers, but not from double neutron star systems. Thus, this kind of search
holds the key to identify the progenitor systems of short GRBs and, in the wait
for gravitational wave detection, represents the only direct way to constrain
the progenitors. We tailored our search to the nature of the expected signal by
properly stretching the observed light curves by an increasing factor with
time, after calibrating the technique on synthetic curves. In none of the GRBs
of our sample we found evidence for periodic or quasiperiodic signals. In
particular, for the 7 unambiguously short GRBs with best S/N we obtained
significant upper limits to the amplitude of the possible oscillations. This
result suggests that BH-NS systems do not dominate the population of short GRB
progenitors as described by the kinematic model of Stone, Loeb, & Berger
(2013).Comment: 7 pages, 5 figures, accepted to ApJ, added reference
A common stochastic process rules gamma-ray burst prompt emission and X-ray flares
Prompt gamma-ray and early X-ray afterglow emission in gamma-ray bursts
(GRBs) are characterized by a bursty behavior and are often interspersed with
long quiescent times. There is compelling evidence that X-ray flares are linked
to prompt gamma-rays. However, the physical mechanism that leads to the complex
temporal distribution of gamma-ray pulses and X-ray flares is not understood.
Here we show that the waiting time distribution (WTD) of pulses and flares
exhibits a power-law tail extending over 4 decades with index ~2 and can be the
manifestation of a common time-dependent Poisson process. This result is robust
and is obtained on different catalogs. Surprisingly, GRBs with many (>=8)
gamma-ray pulses are very unlikely to be accompanied by X-ray flares after the
end of the prompt emission (3.1 sigma Gaussian confidence). These results are
consistent with a simple interpretation: an hyperaccreting disk breaks up into
one or a few groups of fragments, each of which is independently accreted with
the same probability per unit time. Prompt gamma-rays and late X-ray flares are
nothing but different fragments being accreted at the beginning and at the end,
respectively, following the very same stochastic process and likely the same
mechanism.Comment: 11 pages, 7 figures, accepted by Ap
Short gamma-ray bursts within 200 Mpc
We present a systematic search for short-duration gamma-ray bursts (GRBs) in the local Universe based on 14 yr of observations with the Neil Gehrels Swift Observatory. We cross-correlate the GRB positions with the GLADE catalogue of nearby galaxies, and find no event at a distance ≲100 Mpc and four plausible candidates in the range 100 Mpc ≲ D ≲ 200 Mpc. Although affected by low statistics, this number is higher than the one expected for chance alignments to random galaxies, and possibly suggests a physical association between these bursts and nearby galaxies. By assuming a local origin, we use these events to constrain the range of properties for X-ray counterparts of neutron star mergers. Optical upper limits place tight constraints on the onset of a blue kilonova, and imply either low masses (≲10−3M⊙) of lanthanide-poor ejecta or unfavorable orientations (θ_(obs) ≳ 30 deg). Finally, we derive that the all-sky rate of detectable short GRBs within 200 Mpc is 1.3^(+1.7)_(−0.8) yr⁻¹ (68 per cent confidence interval), and discuss the implications for the GRB outflow structure. If these candidates are instead of cosmological origin, we set a upper limit of ≲2.0 yr⁻¹ (90 per cent confidence interval) to the rate of nearby events detectable with operating gamma-ray observatories, such as Swift and Fermi
VizieR Online Data Catalog: Swift GRBs individual power density spectra (Guidorzi+, 2016)
Time intervals, redshifts, best-fit parameters of the power density spectra (PDS) for 215 bright long GRBs observed with the Swift Burst Alert Telescope (BAT) from January 2005 to May 2015. Parameters refer to two alternative PDS models: either a power-law (PL) or a bent power-law (BPL) plus a constant background. (5 data files)
A luminous precursor in the extremely bright GRB 230307A
GRB 230307A is an extremely bright long duration GRB with an observed
gamma-ray fluence of 310 erg cm (10--1000 keV),
second only to GRB 221009A. Despite its long duration, it is possibly
associated with a kilonova, thus resembling the case of GRB 211211A. In analogy
with GRB 211211A, we distinguish three phases in the prompt gamma-ray emission
of GRB 230307A: an initial short duration, spectrally soft emission; a main
long duration, spectrally hard burst; a temporally extended and spectrally soft
tail. We intepret the initial soft pulse as a bright precursor to the main
burst and compare its properties with models of precursors from compact binary
mergers. We find that to explain the brightness of GRB 230307A, a magnetar-like
( G) magnetic field should be retained by the progenitor
neutron star. Alternatively, in the post-merger scenario, the luminous
precursor could point to the formation of a rapidly rotating massive neutron
star.Comment: 9 pages, 5 figures, 2 tables, submitte
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