astro-grb

Nan Liang, Wei Ke Xiao, Yuan Liu, Shuang Nan Zhang

An important issue related to the application of Gamma-Ray Bursts (GRBs) to
cosmology is that the calibration of the luminosity relations of GRBs depends
on the cosmological model due to the lack of sufficient low-redshift GRBs
sample. In this paper, we present a new method to calibrate the GRB relations
in a cosmological model independent way. Since sources at the same redshift
should have the same luminosity distance, we obtain the distance modulus of a
GRB at a given redshift by interpolating from the Hubble diagram of type Ia
Supernovae (SNe Ia) of which the distance moduli are completely cosmological
model independent. Then we calibrate seven GRB luminosity relations without
assuming a particular cosmological model and construct the GRB Hubble diagram
to constrain cosmological parameters. For a flat universe, we obtain
$\Omega_M=0.25_{-0.05}^{+0.04}$ and $\Omega_{\Lambda}=0.75_{-0.04}^{+0.05}$
from 42 GRBs for $1.4<z\le6.6$, which is consistent with the concordance model
in 1-$\sigma$ confidence region.

http://arxiv.org/abs/0802.4262

Y. Jack Ng

Due to quantum fluctuations, spacetime is foamy on small scales. The degree
of foaminess is found to be consistent with holography, a principle prefigured
in the physics of black hole entropy. It has bearing on the ultimate accuracies
of clocks and measurements and the physics of quantum computation. Consistent
with existing archived data on active galactic nuclei from the Hubble Space
Telescope, the application of the holographic spacetime foam model to cosmology
requires the existence of dark energy which, we argue, is composed of an
enormous number of inert “particles” of extremely long wavelength. We suggest
that these “particles” obey infinite statistics in which all representations of
the particle permutation group can occur, and that the nonlocality present in
systems obeying infinite statistics may be related to the nonlocality present
in holographic theories. We also propose to detect spacetime foam by looking
for halos in the images of distant quasars, and argue that it does not modify
the GZK cutoff in the ultra-high energy cosmic ray spectrum and its
contributions to time-of-flight differences of high energy gamma rays from
distant GRB are too small to be detectable.

http://arxiv.org/abs/0801.2962

T. N. Ukwatta, T. Sakamoto, M. Stamatikos, N. Gehrels, K. S. Dhuga

Detecting high-z GRBs is important for constraining the GRB formation rate,
and tracing the history of re-ionization and metallicity of the universe. Based
on the current sample of GRBs detected by Swift with known redshifts, we
investigated the relationship between red-shift, and spectral and temporal
characteristics, using the BAT event-by-event data. We found red-shift trends
for the peak-flux-normalized temporal width T90, the light curve variance, the
peak flux, and the photon index in simple power-law fit to the BAT event data.
We have constructed criteria for screening GRBs with high red-shifts. This will
enable us to provide a much faster alert to the GRB community of possible
high-z bursts.

http://arxiv.org/abs/0802.3815

P.A. Curran (1), R.L.C. Starling (2), P.T. O'Brien (2), O. Godet (2), A.J. van der Horst (3), R.A.M.J. Wijers (1) ((1) University of Amsterdam, (2) University of Leicester, (3) NSSTC)

Previously detected in only a few Gamma-ray Bursts (GRBs), X-ray flares are
now observed in ~50% of all GRBs, though their origins remain unclear. Most
flares are seen early on in the afterglow decay, while some bursts exhibit
flares at late times of 10^4 to 10^5 seconds, which may have implications for
flare models. We investigate whether a sample of late time (> 10^4 s) flares
are different from previous samples of early time flares, or whether they are
merely examples on the tail of the early flare distribution. We examine the
X-ray light curves of Swift bursts for late flares and compare the flare and
underlying power-law properties with those of early flares, and the values of
these properties predicted by the blast wave model. The burst sample show late
flare properties consistent with those of early flares, where the majority of
the flares can be explained by either internal or external shock, though in a
few cases one origin is favoured over the other. The underlying power laws are
mainly consistent with the normal decay phase of the afterglow. If confirmed by
the ever growing sample this would imply that, in some cases, prolonged
activity out to late times or a restarting of the central engine is required.

http://arxiv.org/abs/0802.3803

C. R. A. Augusto, C. E. Navia, K. H. Tsui

Recently, triggers occurring during high background rate intervals have been
reporter by Swift-BAT Gamma Ray Burst (GRB) detector. Among them, there were
two on January 24, two on January 25, and two on February 13, and 18, all in
2008. These Swift-BAT triggers in most cases are probably noise triggers that
occurred while Swift was entering the South Atlantic Anomaly (SAA). In fact, we
show that they happen during a plentiful precipitation of high energy particles
in the SAA, producing muons in the atmosphere detected by two directional
telescopes at sea level, inside the SAA region (Tupi experiment). They look
like sharp peaks in the muon counting rate. In the same category are two
triggers from MILAGRO ground based detector, on January 25 and 31, 2008
respectively. In addition, the trigger coordinates are close to (and, in two
cases, inside) the field of view of the telescopes. From an additional analysis
in the behavior of the muon counting rate, it is possible to conclude that the
events are produced by precipitation of high energy charged particles in the
SAA region. Thus, due to its localization, the Tupi experiment constitutes a
new sensor of high energy particle precipitation in the SAA, and it can be
useful in the identification of some triggers of Gamma Ray Burst detectors.

http://arxiv.org/abs/0802.3845

Yoshiki Kodama (1), Daisuke Yonetoku (1), Toshio Murakami (1), Sachiko Tanabe (1), Ryo Tsutsui (2), Takashi Nakamura (2) ((1) Kanazawa University, (2) Kyoto University)

We calibrated the peak energy-peak luminosity relation of GRBs (so called
Yonetoku relation) using 33 events with the redshift $z < 1.62$ without
assuming any cosmological models. The luminosity distances to GRBs are
estimated from those of large amount of Type Ia supernovae with $z<1.755$. This
calibrated Yonetoku relation can be used as a new cosmic distance ladder toward
higher redshifts. We determined the luminosity distances of 30 GRBs in $1.8 < z
< 5.6$ using the calibrated relation and plotted the likelihood contour in
$(\Omega_m,\Omega_\Lambda)$ plane. We obtained $(\Omega_m, \Omega_{\Lambda})=
(0.26^{+0.05}_{-0.01}, 0.74^{+0.01}_{-0.05})$ for a flat universe. Since our
method is free from the circularity problem, we can say that our universe in
$1.8 < z < 5.6$ is compatible with the so called concordance cosmological model
derived for $z < 1.8$. This suggests that the time variation of the dark energy
is small or zero up to $z\sim 6$.

http://arxiv.org/abs/0802.3428

Nathaniel R. Butler, Daniel Kocevski, Joshua S. Bloom

Several correlations among observables derived from modelling the high-energy
properties of GRBs have been reported in the literature. We show that
well-known examples of these have common features indicative of an origin in
selection effects. In particular, we focus here on the possible origin of the
$E_{\rm pk}$-$E_{\rm iso}$ correlation in Swift data due to detector threshold
truncation. The existence of faint Swift events calls into question inferences
based on pre-Swift surveys which must be subject to complicated incompleteness
effects. We review methods for treating data truncation effects in correlation
analyses and apply these methods to Swift and pre-Swift data. Also, we show
that the $E_{\rm pk}$-$E_{\gamma}$ (”Ghirlanda”) correlation is effectively
independent of the GRB redshifts, which suggests it contains little intrinsic
physics. We recommend verifying that a correlation has significantly reduced
scatter in the rest frame relative to the observer frame and also establishing
that GRB redshifts contribute meaningfully.

http://arxiv.org/abs/0802.3396

F. Iocco, K. Murase, S. Nagataki, P.D. Serpico

We perform a new estimate of the high energy neutrinos expected from GRBs
associated with the first generation of stars in light of new models and
constraints on the epoch of reionization and a more detailed evaluation of the
neutrino emission yields. We also compare the diffuse high energy neutrino
background from Population III stars with the one from “ordinary stars”
(Population II), as estimated consistently within the same cosmological and
astrophysical assumptions. In disagreement with previous literature, we find
that high energy neutrinos from Population III stars will not be observable
with current or near future neutrino telescopes, falling below both IceCube
sensitivity and atmospheric neutrino background under the most extreme
assumptions for the GRB rate. This rules them out as a viable diagnostic tool
for these still elusive metal-free stars.

http://arxiv.org/abs/0707.0515

P.A. Curran (1), A.J. van der Horst (1,2), R.A.M.J. Wijers (1) ((1) University of Amsterdam, The Netherlands, (2)University of Alabama, Huntsville, USA)

Gamma-ray burst afterglow observations in the Swift era have a perceived lack
of achromatic jet breaks compared to the BeppoSAX, or pre-Swift era.
Specifically, relatively few breaks, consistent with jet breaks, are observed
in the X-ray light curves of these bursts. If these breaks are truly missing,
it has serious consequences for the interpretation of GRB jet collimation and
energy requirements, and the use of GRBs as cosmological tools. Here we address
the issue of X-ray breaks that are possibly `hidden' and hence the light curves
are misinterpreted as being single power laws. We do so by synthesising XRT
light curves and fitting both single and broken power laws, and comparing the
relative goodness of each fit via Monte Carlo analysis. Even with the well
sampled light curves of the Swift era, these breaks may be left misidentified,
hence caution is required when making definite statements on the absence of
achromatic breaks.

http://arxiv.org/abs/0710.5285

V. Avila-Reese (1), C. Firmani (1,2), G. Ghisellini (2), J. I. Cabrera (1) ((1)IA-UNAM, Mexico; (2) INAF-OAB, Italy)

Long Gamma-Ray Bursts (GRBs) are the brightest electromagnetic explosions in
the Universe, associated to the death of massive stars. As such, GRBs are
potential tracers of the evolution of the cosmic massive star formation,
metallicity, and Initial Mass Function. GRBs also proved to be appealing
cosmological distance indicators. This opens a unique opportunity to constrain
the cosmic expansion history up to redshifts 5-6. A brief review on both
subjects is presented here.

http://arxiv.org/abs/0802.2578