astro-grb

N. Lyons, P.T. O'Brien, B. Zhang, R. Willingale, E. Troja, R.L.C. Starling

Long duration gamma-ray bursts (GRBs) are thought to be produced by the
core-collapse of a rapidly-rotating massive star. This event generates a highly
relativistic jet and prompt gamma-ray and X-ray emission arises from internal
shocks in the jet or magnetised outflows. If the stellar core does not
immediately collapse to a black hole, it may form an unstable, highly
magnetised millisecond pulsar, or magnetar. As it spins down, the magnetar
would inject energy into the jet causing a distinctive bump in the GRB light
curve where the emission becomes fairly constant followed by a steep decay when
the magnetar collapses. We assume that the collapse of a massive star to a
magnetar can launch the initial jet. By automatically fitting the X-ray
lightcurves of all GRBs observed by the Swift satellite we identified a subset
of bursts which have a feature in their light curves which we call an internal
plateau — unusually constant emission followed by a steep decay — which may
be powered by a magnetar. We use the duration and luminosity of this internal
plateau to place limits on the magnetar spin period and magnetic field strength
and find that they are consistent with the most extreme predicted values for
magnetars.

http://arxiv.org/abs/0908.3798

LIGO Scientific Collaboration, Virgo Collaboration: B. P. Abbott, R. Abbott, F. Acernese, R. Adhikari, P. Ajith, B. Allen, G. Allen, M. Alshourbagy, R. S. Amin, S. B. Anderson, W. G. Anderson, F. Antonucci, S. Aoudia, M. A. Arain, M. Araya, H. Armandula, P. Armor, K. G. Arun, Y. Aso, S. Aston, P. Astone, P. Aufmuth, C. Aulbert, S. Babak, P. Baker, G. Ballardin, S. Ballmer, C. Barker, D. Barker, F. Barone, B. Barr, P. Barriga, L. Barsotti, M. Barsuglia, M. A. Barton, I. Bartos, R. Bassiri, M. Bastarrika, Th. S. Bauer, B. Behnke, M. Beker, M. Benacquista, J. Betzwieser, P. T. Beyersdorf, S. Bigotta, I. A. Bilenko, G. Billingsley, S. Birindelli, R. Biswas, M. A. Bizouard, E. Black, J. K. Blackburn, L. Blackburn, D. Blair, B. Bland, C. Boccara, T. P. Bodiya, L. Bogue, F. Bondu, L. Bonelli, R. Bork, et al. (605 additional authors not shown)

We present the results of a search for gravitational-wave bursts associated
with 137 gamma-ray bursts (GRBs) that were detected by satellite-based
gamma-ray experiments during the fifth LIGO science run and first Virgo science
run. The data used in this analysis were collected from 2005 November 4 to 2007
October 1, and most of the GRB triggers were from the Swift satellite. The
search uses a coherent network analysis method that takes into account the
different locations and orientations of the interferometers at the three
LIGO-Virgo sites. We find no evidence for gravitational-wave burst signals
associated with this sample of GRBs. Using simulated short-duration (<1 s)
waveforms, we set upper limits on the amplitude of gravitational waves
associated with each GRB. We also place lower bounds on the distance to each
GRB under the assumption of a fixed energy emission in gravitational waves,
with typical limits of D ~ 15 Mpc (E_GW^iso / 0.01 M_o c^2)^1/2 for emission at
frequencies around 150 Hz, where the LIGO-Virgo detector network has best
sensitivity. We present astrophysical interpretations and implications of these
results, and prospects for corresponding searches during future LIGO-Virgo
runs.

http://arxiv.org/abs/0908.3824

C. Ledoux, P. M. Vreeswijk, A. Smette, A. J. Fox, P. Petitjean, S. L. Ellison, J. P. U. Fynbo, S. Savaglio

We aim to understand the nature of the absorbing neutral gas in the galaxies
hosting high-redshift long-duration GRBs and to determine their physical
conditions. We report the detection of a significant number of previously
unidentified allowed transition lines of Fe+, involving the fine structure of
the ground term and that of other excited levels, from the zabs=3.969, log
N(H0)=22.10 DLA system located in the host galaxy of GRB 050730. The
time-dependent evolution of the observed Fe+ energy-level populations is
modelled by assuming the excitation mechanism is fluorescence following
excitation by ultraviolet photons. This UV pumping model successfully
reproduces the observations, yielding a burst/cloud distance (defined to the
near-side of the cloud) of d=440\pm 30 pc and a linear cloud size of
l=520{+240}{-190} pc. We discuss these results in the context of no detections
of H2 and CI lines in a sample of seven z>1.8 GRB host galaxies observed with
VLT/UVES. We show that the lack of H2 can be explained by the low
metallicities, [X/H]<-1, low depletion factors and, at most, moderate particle
densities of the systems. This points to a picture where GRB-DLAs typically
exhibiting very high H0 column densities are diffuse metal-poor atomic clouds
with high kinetic temperatures, Tkin>~1000 K, and large physical extents,
l>~100 pc. The properties of GRB-DLAs observed at high spectral resolution
towards bright GRB afterglows differ markedly from the high metal and dust
contents of GRB-DLAs observed at lower resolution. This difference likely
results from the effect of a bias, against systems of high metallicity and/or
close to the GRB, due to dust obscuration in the magnitude-limited GRB
afterglow samples observed with high-resolution spectrographs.

http://arxiv.org/abs/0907.1057

Ming Xu, Y. F. Huang

The Galactic hard X-ray transient SWIFT J195509+261406 was first observed as
a gamma-ray burst GRB 070610. Within 3 days after the burst, more than forty
optical flares had been observed. Here we propose that this peculiar event
should be associated with a white dwarf. The hard X-ray burst itself may be
triggered by the collision between two planets orbiting the white dwarf. Some
cracked frag-ments produced in the collision then fall onto the surface of the
white dwarf in several days, giving birth to the observed optical flares via
cyclotron radiation. Our model can satisfactorily explain the basic features of
the observations.

http://arxiv.org/abs/0908.3226

S. W. Kong, Y. F. Huang, K. S. Cheng, T. Lu

Extensive multi-band afterglow data are available for GRB 980703. Especially,
its radio afterglow was very bright and was monitored until more than 1000 days
after the trigger time. Additionally, there is no obvious special feature,
i.e., no rebrightenings, no plateau, and no special steep decay or slow decay
in the multi-band afterglow light curves. All these conditions make GRB 980703
a precious sample in gamma-ray burst research. Here we use the observational
data of GRB 980703 to test the standard fireball model in depth. It is found
that the model can give a satisfactory explanation to the multi-band and
overall afterglow light curves. The beaming angle of GRB 980703 is derived as
~0.23 radian, and the circum-burst medium density is ~ 27 cm-3. The total
isotropic equivalent kinetic energy of the ejecta is ~ 3.8E52 ergs. A
rest-frame extinction of Av ~ 2.5 mag in the host galaxy is also derived.

http://arxiv.org/abs/0908.2850

S. W. Kong, Y. F. Huang, K. S. Cheng, T. Lu

Extensive multi-band afterglow data are available for GRB 980703. Especially,
its radio afterglow was very bright and was monitored until more than 1000 days
after the trigger time. Additionally, there is no obvious special feature,
i.e., no rebrightenings, no plateau, and no special steep decay or slow decay
in the multi-band afterglow light curves. All these conditions make GRB 980703
a precious sample in gamma-ray burst research. Here we use the observational
data of GRB 980703 to test the standard fireball model in depth. It is found
that the model can give a satisfactory explanation to the multi-band and
overall afterglow light curves. The beaming angle of GRB 980703 is derived as
~0.23 radian, and the circum-burst medium density is ~ 27 cm-3. The total
isotropic equivalent kinetic energy of the ejecta is ~ 3.8E52 ergs. A
rest-frame extinction of Av ~ 2.5 mag in the host galaxy is also derived.

http://arxiv.org/abs/0908.2850

Shlomo Dado, Arnon Dar

The master formulae of the CB model of long durations gamma ray bursts (GRBs)
which reproduce very well the light curves and spectral evolution of their
prompt emission pulses and their smooth afterglows, also reproduce very well
the lightcurves and spectral evolution of their X-ray and optical flares. Here
we demonstrate that for GRB090812

http://arxiv.org/abs/0908.2849

Rudy C. Gilmore, Francisco Prada, Joel R. Primack

Gamma rays from extragalactic sources are attenuated by pair-production
interactions with diffuse photons of the extragalactic background light (EBL).
Gamma-ray bursts (GRBs) are a source of high-redshift photons above 10 GeV, and
could be therefore useful as a probe of the evolving UV background radiation.
In this paper, we develop a simple phenomenological model for the number and
redshift distribution of gamma-ray bursts that can be seen at GeV energies with
the Fermi satellite and MAGIC atmospheric Cherenkov telescope. We estimate the
observed number of gamma rays per year, and show how this result is modified by
considering interactions with different realizations of the evolving EBL. We
also discuss the bright Fermi GRB 080916C in the context of this model. We find
that the LAT on Fermi can be expected to see a small number of photons above 10
GeV each year from distant GRBs. Annual results for ground-based instruments
like MAGIC are highly variable due to the low duty cycle and sky coverage of
the telescope. However, successfully viewing a bright or intermediate GRB from
the ground could provide hundreds of photons from high redshift, which would
almost certainly be extremely useful in constraining both GRB physics and the
high-redshift EBL.

http://arxiv.org/abs/0908.2830

A. M. Soderberg, S. Chakraborti, G. Pignata, R. A. Chevalier, P. Chandra, A. Ray, M. H. Wieringa, A. Copete, V. Chaplin, V. Connaughton, S. D. Barthelmy, M. F. Bietenholz, N. Chugai, M. D. Stritzinger, M. Hamuy, C. Fransson, O. Fox, E. M. Levesque, J. E. Grindlay, P. Challis, R. J. Foley, R. P. Kirshner, P. A. Milne, M. A. P. Torres

Type Ibc supernovae (SNe Ibc) mark the gravitational collapse of some massive
stars (M > 20 Msun) propelling several solar masses of material to typical
velocities of ~10,000 km/s. The closely-related but exceedingly rare class of
long-duration gamma-ray bursts (GRBs) produce, in addition, a relativistic
outflow powered by a central engine (accreting black hole or neutron star) and
have been found exclusively through their gamma-ray signal. Here we report the
discovery of luminous radio emission from the seemingly ordinary Type Ibc SN
2009bb which outshines that of all other SNe Ibc observed on a comparable
timescale. These observations require a substantial mildly-relativistic outflow
and indicate that the explosion was powered by a central engine, thus
representing the first such event discovered without the aid of a gamma-ray
trigger. A comparison with our extensive radio survey of SNe Ibc reveals that
the fraction of such events is low (roughly 1 percent), measured independently
from, and yet consistent with, the inferred rate of nearby GRBs. This discovery
marks the observational realization that long-wavelength surveys will soon
rival gamma-ray satellites in pinpointing nearby engine-driven explosions.

http://arxiv.org/abs/0908.2817

G. Ghirlanda (1), L. Nava (1,2), G. Ghisellini (1) ((1)INAF-Osservatorio Astronomico di Brera, (2)Universita' dell'Insubria)

We study the spectra of all long Gamma Ray Bursts (GRBs) of known redshift
detected by the Fermi satellite. Their fluxes and fluences are large enough to
allow a time dependent study of their spectral characteristics in the 8 keV-1
MeV energy range. We find that the peak energy Ep of their EL(E) spectrum
correlates with the luminosity in a remarkable tight way within individual
bursts. This time resolved Ep-Liso correlation is very similar for all the
considered bursts, and has a slope and normalisation similar to the analogous
Ep-Liso correlation defined by the time integrated spectra of different bursts
detected by several different satellites. For a few of the considered GRBs, we
could also study the behaviour of the Ep-Liso correlation during the rising and
decaying phases of individual pulses within each burst, finding no differences.
Our results indicate the presence of a similar physical mechanism, operating
for the duration of different GRBs, linking tightly the burst luminosity with
the peak energy of the spectrum emitted at different times. Such a physical
mechanism is the same during the rise and decay phase of individual pulses
composing a GRB. These results, while calling for a robust physical
interpretation, strongly indicate that the Ep-Liso spectral energy correlation
found considering the time integrated spectra of different bursts is real, and
not the result of instrumental selection effects.

http://arxiv.org/abs/0908.2807