astro-grb

Jorick S. Vink (Armagh Observatory)

We discuss the role of mass loss for the evolution of the most massive stars,
highlighting the role of the predicted bi-stability jump that might be relevant
for the evolution of rotational velocities during or just after the main
sequence. This mechanism is also proposed as an explanation for the mass-loss
variations seen in the winds from Luminous Blue Variables (LBVs). These might
be relevant for the quasi-sinusoidal modulations seen in a number of recent
transitional supernovae (SNe), as well as for the double-throughed absorption
profile recently discovered in the Halpha line of SN 2005gj. Finally, we
discuss the role of metallicity via the Z-dependent character of their winds,
during both the initial and final (Wolf-Rayet) phases of evolution, with
implications for the angular momentum evolution of the progenitor stars of long
gamma-ray bursts (GRBs).

http://arxiv.org/abs/0809.4789

Michael Stamatikos, Takanori Sakamoto, David L. Band

We discuss the preliminary results of spectral analysis simulations involving
anticipated correlated multi-wavelength observations of gamma-ray bursts (GRBs)
using Swift's Burst Alert Telescope (BAT) and the Gamma-Ray Large Area Space
Telescope's (GLAST) Burst Monitor (GLAST-GBM), resulting in joint spectral
fits, including characteristic photon energy (Epeak) values, for a conservative
annual estimate of ~30 GRBs. The addition of BAT's spectral response will (i)
complement in-orbit calibration efforts of GBM's detector response matrices,
(ii) augment GLAST's low energy sensitivity by increasing the ~20-100 keV
effective area, (iii) facilitate ground-based follow-up efforts of GLAST GRBs
by increasing GBM's source localization precision, and (iv) help identify a
subset of non-triggered GRBs discovered via off-line GBM data analysis. Such
multi-wavelength correlative analyses, which have been demonstrated by
successful joint-spectral fits of Swift-BAT GRBs with other higher energy
detectors such as Konus-WIND and Suzaku-WAM, would enable the study of
broad-band spectral and temporal evolution of prompt GRB emission over three
energy decades, thus potentially increasing the science return without placing
additional demands upon mission resources throughout their contemporaneous
orbital tenure over the next decade.

http://arxiv.org/abs/0809.4724

A. Stefanescu, G. Kanbach, A. Słowikowska, J. Greiner, S. McBreen, G. Sala

Highly luminous rapid flares are characteristic of processes around compact
objects like white dwarfs, neutron stars or black holes. In the high energy
regime of X- and gamma-rays, outbursts with variability time-scales of seconds
and faster are routinely observed, e.g. in gamma-ray bursts or Soft Gamma
Repeaters. In the optical, flaring activity on such time-scales has never been
observed outside the prompt phase of GRBs. This is mostly due to the fact that
outbursts with strong, fast flaring usually are discovered in the high-energy
regime. Most optical follow-up observations of such transients employ
instruments with integration times exceeding tens of seconds, which are
therefore unable to resolve fast variability. Here we show the observation of
extremely bright and rapid optical flaring in the galactic transient SWIFT
J195509.6+261406. Flaring of this kind has never previously been reported. Our
optical light-curves are phenomenologically similar to high energy light-curves
of Soft Gamma Repeaters and Anomalous X-ray Pulsars, which are thought to be
neutron stars with extremely high magnetic fields (magnetars). This suggests
similar emission processes may be at work, but in contrast to the other known
magnetars with strong emission in the optical.

http://arxiv.org/abs/0809.4043

P. W. A. Roming, T. S. Koch, S. R. Oates, B. L. Porterfield, D. E. Vanden Berk, P. T. Boyd, S. T. Holland, E. A. Hoversten, S. Immler, F. E. Marshall, M. J. Page, J. L. Racusin, D. P. Schneider, A. A. Breeveld, P. J. Brown, M. M. Chester, A. Cucchiara, M. De Pasquale, C. Gronwall, S. D. Hunsberger, N. P. M. Kuin, W. B. Landsman, P. Schady, M. Still

We present the first Swift Ultra-Violet/Optical Telescope (UVOT) gamma-ray
burst (GRB) afterglow catalog. The catalog contains data from over 64,000
independent UVOT image observations of 229 GRBs first detected by Swift, the
High Energy Transient Explorer 2 (HETE2), the INTErnational Gamma-Ray
Astrophysics Laboratory (INTEGRAL), and the Interplanetary Network (IPN). The
catalog covers GRBs occurring during the period from 2005 Jan 17 to 2007 Jun 16
and includes ~86% of the bursts detected by the Swift Burst Alert Telescope
(BAT). The catalog provides detailed burst positional, temporal, and
photometric information extracted from each of the UVOT images. Positions for
bursts detected at the 3-sigma-level are provided with a nominal accuracy,
relative to the USNO-B1 catalog, of ~0.25 arcseconds. Photometry for each burst
is given in three UV bands, three optical bands, and a 'white' or open filter.
Upper limits for magnitudes are reported for sources detected below 3-sigma.
General properties of the burst sample and light curves, including the
filter-dependent temporal slopes, are also provided. The majority of the UVOT
light curves, for bursts detected at the 3-sigma-level, can be fit by a single
power-law, with a median temporal slope (alpha) of 0.96, beginning several
hundred seconds after the burst trigger and ending at ~1×10^5 s. The median
UVOT v-band (~5500 Angstroms) magnitude at 2000 s for a sample of “well”
detected bursts is 18.02. The UVOT flux interpolated to 2000 s after the burst,
shows relatively strong correlations with both the prompt Swift BAT fluence,
and the Swift X-ray flux at 11 hours after the trigger.

http://arxiv.org/abs/0809.4193

L. Amati, C. Guidorzi, F. Frontera, M. Della Valle, F. Finelli, R. Landi, E. Montanari

We have used the Ep,i-Eiso correlation of GRBs to measure the cosmological
parameter Omega_M. By adopting a maximum likelihood approach which allows us to
correctly quantify the extrinsic (i.e. non–Poissonian) scatter of the
correlation, we constrain (for a flat universe) Omega_M to 0.04-0.40 (68%
confidence level), with a best fit value of Omega_M ~ 0.15, and exclude Omega_M
= 1 at 99.9% confidence level. If we release the assumption of a flat universe,
we still find evidence for a low value of Omega_M (0.04-0.50 at 68% confidence
level) and a weak dependence of the dispersion of the Ep,i-Eiso correlation on
Omega_Lambda (with an upper limit of Omega_Lambda ~ 1.15 at 90% confidence
level). Our approach makes no assumptions on the Ep,i-Eiso correlation and it
does not use other calibrators to set the “zero' point of the relation,
therefore our treatment of the data is not affected by circularity and the
results are independent of those derived via type Ia SNe (or other cosmological
probes). Unlike other multi-parameters correlations, our analysis grounds on
only two parameters, then including a larger number (a factor ~3) of GRBs and
being less affected by systematics. Simulations based on realistic
extrapolations of ongoing (and future) GRB experiments (e.g., Swift,
Konus-Wind, GLAST) show that: i) the uncertainties on cosmological parameters
can be significantly decreased; ii) future data will allow us to get clues on
the “dark energy” evolution.

http://arxiv.org/abs/0805.0377

D. A. Perley, W. Li, R. Chornock, J. X. Prochaska, N. R. Butler, P. Chandra, L. K. Pollack, J. S. Bloom, A. V. Filippenko, H. Swan, F. Yuan, C. Akerlof, M. W. Auger, S. B. Cenko, H.-W. Chen, C. D. Fassnacht, D. Fox, D. Frail, E. M. Johansson, D. Le Mignant, T. McKay, M. Modjaz, W. Rujopakarn, R. Russell, M. A. Skinner, G. H. Smith, I. Smith, M. A. van Dam, S. Yost

The optical afterglow of long-duration GRB 071003 is among the brightest yet
to be detected from any GRB, with R ~ 12 mag in KAIT observations starting 42 s
after the GRB trigger, including filtered detections during prompt emission.
However, our high S/N ratio afterglow spectrum displays only extremely weak
absorption lines at what we argue is the host redshift of z = 1.60435 - in
contrast to the three other, much stronger Mg II absorption systems observed at
lower redshifts. Together with Keck adaptive optics observations which fail to
reveal a host galaxy coincident with the burst position, our observations
suggest a halo progenitor and offer a cautionary tale about the use of Mg II
for GRB redshift determination. We present early through late-time observations
spanning the electromagnetic spectrum, constrain the connection between the
prompt emission and early variations in the light curve (we observe no
correlation), and discuss possible origins for an unusual, marked rebrightening
that occurs a few hours after the burst: likely either a late-time refreshed
shock or a wide-angle secondary jet. Analysis of the late-time afterglow is
most consistent with a wind environment, suggesting a massive star progenitor.
Together with GRB 070125, this may indicate that a small but significant
portion of star formation in the early universe occurred far outside what we
consider a normal galactic disk.

http://arxiv.org/abs/0805.2394

Charles D. Dermer (NRL), Chris L. Fryer (LANL)

Gamma-ray bursts (GRBs) are a mixed class of sources consisting of, at least,
the long duration and short-hard subclasses, the X-ray flashes, and the
low-luminosity GRBs. In all cases, the release of enormous amounts of energy on
a short timescale makes an energetic, relativistic or mildly relativistic
fireball that expands until it reaches a coasting Lorentz factor determined by
the amount of baryons mixed into the fireball. Radiation is produced when the
blast wave interacts with the surrounding medium at an external shock, or when
shell collisions dissipate kinetic energy at internal shocks. This series of
notes is organized as follows: (1) The observational situation of GRBs is
summarized; (2) Progenitor models of GRBs are described; (3) An overview of the
the blast-wave physics used to model leptonic emissions is given; (4) GRB
physics is applied to hadronic acceleration and ultra-high energy cosmic ray
production; (5) Prospects for GRB physics and gamma-ray astronomy with the
Fermi Gamma-ray Space Telescope (FGST, formerly GLAST), and space-based and
ground-based observatories are considered. Also included are exercises and
problems.

http://arxiv.org/abs/0809.3959

M. Marisaldi, C. Labanti, F. Fuschino, M. Galli, A. Argan, G. Barbiellini, M. Basset, F. Boffelli, A. Bulgarelli, P. Caraveo, P. W. Cattaneo, A. Chen, V. Cocco, E. Costa, F. D'Ammando, E. Del Monte, G. De Paris, G. Di Cocco, G. Di Persio, I. Donnarumma, Y. Evangelista, M. Feroci, A. Ferrari, M. Fiorini, L. Foggetta, T. Froysland, M. Frutti, F. Gianotti, A. Giuliani, I. Lapshov, F. Lazzarotto, F. Liello, P. Lipari, F. Longo, M. Mastropietro, E. Mattaini, A. Mauri, F. Mauri, S. Mereghetti, E. Morelli, A. Morselli, L. Pacciani, A. Pellizzoni, F. Perotti, P. Picozza, C. Pontoni, G. Porrovecchio, M. Prest, G. Pucella, M. Rapisarda, A. Rappoldi, E. Rossi, A. Rubini, P. Soffitta, M. Tavani, A. Traci, M. Trifoglio, A. Trois, E. Vallazza, S. Vercellone, V. Vittorini, A. Zambra, D. Zanello, C. Pittori, et al. (9 additional authors not shown)

The Mini-Calorimeter (MCAL) instrument on-board the AGILE satellite is a
non-imaging gamma-ray scintillation detector sensitive in the 300keV-100MeV
energy range with a total on-axis geometrical area of 1400cm^2. Gamma-Ray
Bursts (GRBs) are one of the main scientific targets of the AGILE mission and
the MCAL design as an independent self-triggering detector makes it a valuable
all-sky monitor for GRBs. Furthermore MCAL is one of the very few operative
instruments with microsecond timing capabilities in the MeV range. In this
paper the results of GRB detections with MCAL after one year of operation in
space are presented and discussed. A flexible trigger logic implemented in the
AGILE payload data-handling unit allows the on-board detection of GRBs. For
triggered events, energy and timing information are sent to telemetry on a
photon-by-photon basis, so that energy and time binning are limited by counting
statistics only. When the trigger logic is not active, GRBs can be detected
offline in ratemeter data, although with worse energy and time resolution.
Between the end of June 2007 and June 2008 MCAL detected 51 GRBs, with a
detection rate of about 1 GRB/week, plus several other events at a few
milliseconds timescales. Since February 2008 the on-board trigger logic has
been fully active. Comparison of MCAL detected events and data provided by
other space instruments confirms the sensitivity and effective area
estimations. MCAL also joined the 3rd Inter-Planetary Network, to contribute to
GRB localization by means of triangulation.

http://arxiv.org/abs/0809.3917

Zoltan Haiman (Columbia University)

The high sensitivity of JWST will open a new window on the end of the
cosmological dark ages. Small stellar clusters, with a stellar mass of several
10^6 M_sun, and low-mass black holes (BHs), with a mass of several 10^5 M_sun
should be directly detectable out to redshift z=10, and individual supernovae
(SNe) and gamma ray burst (GRB) afterglows are bright enough to be visible
beyond this redshift. Dense primordial gas, in the process of collapsing from
large scales to form protogalaxies, may also be possible to image through
diffuse recombination line emission, possibly even before stars or BHs are
formed. In this article, I discuss the key physical processes that are expected
to have determined the sizes of the first star-clusters and black holes, and
the prospect of studying these objects by direct detections with JWST and with
other instruments. The direct light emitted by the very first stellar clusters
and intermediate-mass black holes at z>10 will likely fall below JWST's
detection threshold. However, JWST could reveal a decline at the faint-end of
the high-redshift luminosity function, and thereby shed light on radiative and
other feedback effects that operate at these early epochs. JWST will also have
the sensitivity to detect individual SNe from beyond z=10. In a dedicated
survey lasting for several weeks, thousands of SNe could be detected at z>6,
with a redshift distribution extending to the formation of the very first stars
at z>15. Using these SNe as tracers may be the only method to map out the
earliest stages of the cosmic star-formation history. Finally, we point out
that studying the earliest objects at high redshift will also offer a new
window on the primordial power spectrum, on 100 times smaller scales than
probed by current large-scale structure data.

http://arxiv.org/abs/0809.3926

Z. Y. Peng, R. J. Lu, L. M. Fang, Y. Y. Bao, Y. Yin

Employing a sample presented by Kaneko et al. (2006) and Kocevski et al.
(2003), we select 42 individual tracking pulses (here we defined tracking as
the cases in which the hardness follows the same pattern as the flux or count
rate time profile) within 36 Gamma-ray Bursts (GRBs) containing 527
time-resolved spectra and investigate the spectral hardness, $E_{peak}$ (where
$E_{peak}$ is the maximum of the $\nu F_{\nu}$ spectrum), evolutionary
characteristics. The evolution of these pulses follow soft-to-hard-to-soft (the
phase of soft-to-hard and hard-to-soft are denoted by rise phase and decay
phase, respectively) with time. It is found that the overall characteristics of
$E_{peak}$ of our selected sample are: 1) the $E_{peak}$ evolution in the rise
phase always start on the high state (the values of $E_{peak}$ are always
higher than 50 keV); 2) the spectra of rise phase clearly start at higher
energy (the median of $E_{peak}$ are about 300 keV), whereas the spectra of
decay phase end at much lower energy (the median of $E_{peak}$ are about 200
keV); 3) the spectra of rise phase are harder than that of the decay phase and
the duration of rise phase are much shorter than that of decay phase as well.
In other words, for a complete pulse the initial $E_{peak}$ is higher than the
final $E_{peak}$ and the duration of initial phase (rise phase) are much
shorter than the final phase (decay phase). This results are in good agreement
with the predictions of Lu et al. (2007) and current popular view on the
production of GRBs. We argue that the spectral evolution of tracking pulses may
be relate to both of kinematic and dynamic process even if we currently can not
provide further evidences to distinguish which one is dominant. Moreover, our
statistical results give some witnesses to constrain the current GRB model.

http://arxiv.org/abs/0809.3620