astro-grb

He Gao, Nan Liang, Zong-Hong Zhu

For the use of Gamma-Ray Bursts (GRBs) to probe cosmology in a
cosmology-independent way, a new method has been proposed to obtain luminosity
distances of GRBs by interpolating directly from the Hubble diagram of SNe Ia,
and then calibrating GRB relations at high redshift. In this paper, following
the basic assumption in the interpolation method that objects at the same
redshift should have the same luminosity distance, we propose another approach
to calibrate GRB luminosity relations with cosmographic fitting directly from
SN Ia data. In cosmography, there is a well-known fitting formula which can
reflect the Hubble relation between luminosity distance and redshift with
cosmographic parameters which can be fitted from observation data. Using the
Cosmographic fitting results from the Union set of SNe Ia, we calibrate five
GRB relations using GRB sample at $z\leq1.4$ and deduce distance moduli of GRBs
at $1.4< z \leq 6.6$ by generalizing above calibrated relations at high
redshift. Finally, we constrain the dark energy parameterization models of the
Chevallier-Polarski-Linder (CPL) model and the Jassal-Bagla-Padmanabhan (JBP)
model with GRB data at high redshift, as well as with the Cosmic Microwave
Background radiation (CMB) and the baryonic acoustic oscillation (BAO)
observations, and we find the $\Lambda$CDM model is consistent with the current
data in 1-$\sigma$ confidence region.

http://arxiv.org/abs/1003.5755

C. Dermer (NRL)

If gamma-ray bursts are sources of ultra-high energy cosmic rays, then
radiative signatures of hadronic acceleration are expected in GRB data.
Observations with the Fermi Gamma-ray Space Telescope offer the best means to
search for evidence of UHECRs in GRBs through electromagnetic channels. Various
issues related to UHECR acceleration in GRBs are reviewed, with a focus on the
question of energetics.

http://arxiv.org/abs/1003.5318

Denitsa R. Staicova, Plamen P. Fiziev

We give a new theoretical basis for examination of the presence of the Kerr
black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of
different astrophysical objects like X-ray binary systems, gamma ray bursts
(GRBs), active galactic nuclei (AGN), etc. Our method is based on the study of
spectra of the relativistic jets, typically formed around these objects. Such
theoretical spectra are calculated numerically for the first time. Our main
result is a detailed description of the qualitative change of the behavior of
electromagnetic jet frequencies under the transition from the KBH to the KNS,
considered here as a bifurcation of the Kerr metric. We show that quite
surprisingly our novel electromagnetic jet spectra describe linearly stable
electromagnetic jets from both the KBH and the KNS. Numerical investigation of
the dependence of these jet spectra on the rotation of the Kerr metric is
presented and discussed. It is based on the study of the corresponding exact
solutions of the Teukolsky master equation for electromagnetic perturbations of
the Kerr metric.

http://arxiv.org/abs/1002.0480

Tong Liu, En-Wei Liang, Wei-Min Gu, Xiao-Hong Zhao, Zi-Gao Dai, Ju-Fu Lu

A model of jet precession driven by a neutrino-cooled disc around a spinning
black hole is present in order to explain the temporal structure and spectral
evolution of gamma-ray bursts (GRBs). The differential rotation of the outer
part of a neutrino dominated accretion disc may result in precession of the
inner part of the disc and the central black hole, hence drives a precessed jet
via neutrino annihilation around the inner part of the disc. Both analytic and
numeric results for our model are present. Our calculations show that a black
hole-accretion disk system with black hole mass $M \simeq 3.66 M_\odot$,
accretion rate $\dot{M} \simeq 0.54 M_\odot \rm s^{-1}$, spin parameter $a=0.9$
and viscosity parameter $\alpha=0.01$ may drive a precessed jet with period P=1
s and luminosity $L=10^{51}$ erg s$^{-1}$, corresponding to the scenario for
long GRBs. A precessed jet with $P=0.1$s and $L=10^{50}$ erg s$^{-1}$ may be
powered by a system with $M \simeq 5.59 M_\odot$, $\dot{M} \simeq 0.74 M_\odot
\rm s^{-1}$, $a=0.1$, and $\alpha=0.01$, possibly being responsible for the
short GRBs. Both the temporal and spectral evolution in GRB pulse may explained
with our model. GRB central engines likely power a precessed jet driven by a
neutrino-cooled disc. The global GRB lightcurves thus could be modulated by the
jet precession during the accretion timescale of the GRB central engine. Both
the temporal and spectral evolution in GRB pulse may be due to an viewing
effect due to the jet precession.

http://arxiv.org/abs/1003.4883

Julia K. Becker, Francis Halzen, Aongus O'Murchadha, Martino Olivo

Gamma-ray bursts have the potential to produce the particle energies (up to
$10^{21}$\,eV) and the energy budget ($10^{44}\, \rm{erg\, yr^{-1}\,
Mpc^{-3}}$) to accommodate the spectrum of the highest energy cosmic rays; on
the other hand, there is no observational evidence that they accelerate
hadrons. The Fermi GST recently observed two bursts that exhibit a power-law
high-energy extension of the typical (Band) photon spectrum that extends to
$\sim 30$ GeV. On the basis of fireball phenomenology we argue that they, along
with GRB941017 observed by EGRET in 1994, show indirect evidence for
considerable baryon loading. Since the detection of neutrinos is the only
unambiguous way to establish that GRBs accelerate protons, we use two methods
to estimate the neutrino flux produced when they interact with fireball photons
to produce charged pions and neutrinos. While the number of events expected
from the Fermi bursts detected to date is small, we conclude that an event like
GRB941017 will be detected by the IceCube neutrino telescope if gamma-ray
bursts are indeed the sources of the observed cosmic rays.

http://arxiv.org/abs/1003.4710

T. N. Ukwatta, Jane H. MacGibbon, W. C. Parke, K. S. Dhuga, S. Rhodes, A. Eskandarian, N. Gehrels, L. Maximon, D. C. Morris

Primordial Black Holes (PBHs), which may have been created in the early
Universe, are predicted to be detectable by their Hawking radiation. The Fermi
Gamma-ray Space Telescope observatory offers increased sensitivity to the
gamma-ray bursts produced by PBHs with an initial mass of $\sim 5\times
10^{14}$ g expiring today. PBHs are candidate progenitors of unidentified
Gamma-Ray Bursts (GRBs) that lack X-ray afterglow. We propose spectral lag,
which is the temporal delay between the high and low energy pulses, as an
efficient method to identify PBH evaporation events with the Fermi Large Area
Telescope (LAT).

http://arxiv.org/abs/1003.4515

B. McBreen, S. Foley, L. Hanlon

It is now more than 40 years since the discovery of gamma-ray bursts (GRBs)
and in the last two decades there has been major progress in the observations
of bursts, the afterglows and their host galaxies. This recent progress has
been fueled by the ability of gamma-ray telescopes to quickly localise GRBs and
the rapid follow-up observations with multi-wavelength instruments in space and
on the ground. A total of 674 GRBs have been localised to date using the coded
aperture masks of the four gamma-ray missions, BeppoSAX, HETE II, INTEGRAL and
Swift. As a result there are now high quality observations of more than 100
GRBs, including afterglows and host galaxies, revealing the richness and
progress in this field. The observations of GRBs cover more than 20 orders of
magnitude in energy, from 10^-5 eV to 10^15 eV and also in two
non-electromagnetic channels, neutrinos and gravitational waves. However the
continuation of progress relies on space based instruments to detect and
rapidly localise GRBs and distribute the coordinates.

http://arxiv.org/abs/1003.4440

S. Covino

GRB afterglows are among the best examples of astrophysical sources requiring
a true multiwavelength observational approach. Radiation processes and main
physical ingredients can only be disentangled with knowledge of their spectral
and temporal properties through the largest possible band, i.e. from the X-ray
down to radio. We now briefly review some of the most relevant observational
findings recently obtained through optical observations.

http://arxiv.org/abs/1003.3911

Luigi Foschini

Let's take stock of the situation on one of the most studied astrophysical
phenomena during the latest years: the jets escaping from protostars, stellar
singularities, GRB and active galactic nuclei.

http://arxiv.org/abs/1003.4212

S. B. Pandey, C. A. Swenson, D. A. Perley, C. Guidorzi, K. Wiersema, D. Malesani, C. Akerlof, M. C. B. Ashley, D. Bersier, Z. Cano, A. Gomboc, I. Ilyin, P. Jakobsson, I. K. W. Kleiser, S. Kobayashi, C. Kouveliotou, A. J. Levan, T. A. McKay, A. Melandri, C. J. Mottram, C. G. Mundell, P. T. O'Brien, A. Phillips, J. M. Rex, M. H. Siegel, R. J. Smith, I. A. Steele, G. Stratta, N. R. Tanvir, D. Weights, S. A. Yost, F. Yuan, W. Zheng

The optical-infrared afterglow of the LAT-detected long duration burst, GRB
090902B, has been observed by several instruments. The earliest detection by
ROTSE-IIIa occurred 80 minutes after detection by the GBM instrument onboard
the Fermi Gamma-Ray Space Telescope, revealing a bright afterglow and a decay
slope suggestive of a reverse shock origin. Subsequent optical-IR observations
followed the light curve for 6.5 days. The temporal and spectral behavior at
optical-infrared frequencies is consistent with synchrotron fireball model
predictions; the cooling break lies between optical and XRT frequencies ~ 1.9
days after the burst. The inferred electron energy index is $p = 1.8 \pm 0.2$,
which would however imply an X-ray decay slope flatter than observed. The XRT
and LAT data have similar spectral indices and the observed steeper value of
the LAT temporal index is marginally consistent with the predicted temporal
decay in the radiative regime of the forward shock model. Absence of a jet
break during the first 6 days implies a collimation-corrected $\gamma$-ray
energy $E_{\gamma} > 2.2\times10^{52}\rm$ ergs, one of the highest ever seen in
a long-duration GRBs. More events combining GeV photon emission with
multi-wavelength observations will be required to constrain the nature of the
central engine powering these energetic explosions and to explore the
correlations between energetic quanta and afterglow emission.

http://arxiv.org/abs/1003.4250