148 research outputs found
GRB Astrophysics in the Swift Era and Beyond
Gamma-ray Bursts (GRBs) are relativistic cosmological beacons of transient
high energy radiation whose afterglows span the electromagnetic spectrum.
Theoretical expectations of correlated neutrino emission position GRBs at an
astrophysical nexus for a metamorphosis in our understanding of the Cosmos.
This new dawn in the era of experimental (particle) astrophysics and cosmology
is afforded by current facilities enabling the novel astronomy of high energy
neutrinos, in concert with unprecedented electromagnetic coverage. In that
regard, GRBs represent a compelling scientific theme that may facilitate
fundamental breakthroughs in the context of Swift, Fermi and IceCube.
Scientific synergy will be achieved by leveraging the combined sensitivity of
contemporaneous ground-based and satellite observatories, thus optimizing their
collective discovery potential. Hence, the advent of GRB multi-messenger
astronomy may cement an explicit connection to fundamental physics, via nascent
cosmic windows, throughout the next decade.Comment: 5 pages, 1 figure. Contributed to the Proceedings of the 2nd
Heidelberg Workshop: High-Energy Gamma-rays and Neutrinos from Extra-Galactic
Sources (Max Planck Institute for Nuclear Physics
Correlative Spectral Analysis of Gamma-Ray Bursts using Swift-BAT and GLAST-GBM
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.Comment: 5 pages. Adapted from a contribution to the Proceedings of the 2008
Nanjing GRB Conference. Edited by Y. F. Huang, Z. G. Dai and B. Zhan
A Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRBs?
We report on observations of correlated behavior between the prompt gamma-ray
and optical emission from GRB 080319B, which (i) strongly suggest that they
occurred within the same astrophysical source region and (ii) indicate that
their respective radiation mechanisms were most likely dynamically coupled. Our
preliminary results, based upon a new cross-correlation function (CCF)
methodology for determining the time-resolved spectral lag, are summarized as
follows. First, the evolution in the arrival offset of prompt gamma-ray photon
counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic
gamma-ray spectral lag) appears to be anti-correlated with the arrival offset
between prompt 15-350 keV gamma-rays and the optical emission observed by
TORTORA (extrinsic optical/gamma-ray spectral lag), thus effectively
partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, prompt
optical emission is nested within intervals of (a) trivial intrinsic gamma-ray
spectral lag (~T+12+-2 and ~T+50+/-2 sec) with (b) discontinuities in the hard
to soft evolution of the photon index for a power law fit to 15-150 keV
Swift-BAT data (~T+8+/-2 and ~T+48+/-1 sec), both of which coincide with the
rise (~T+10+/-1 sec) and decline (~T+50+/-1 sec) of prompt optical emission.
This potential discovery, robust across heuristic permutations of BAT energy
channels and varying temporal bin resolution, provides the first observational
evidence for an implicit connection between spectral lag and the dynamics of
shocks in the context of canonical fireball phenomenology.Comment: 5 pages. Adapted from a contribution to the Proceedings of the 2008
Nanjing GRB Conference. Edited by Y. F. Huang, Z. G. Dai and B. Zhan
The Correlation of Spectral Lag Evolution with Prompt Optical Emission in GRB 080319B
We report on observations of correlated behavior between the prompt gamma-ray
and optical emission from GRB 080319B, which confirm that (i) they occurred
within the same astrophysical source region and (ii) their respective radiation
mechanisms were dynamically coupled. Our results, based upon a new CCF
methodology for determining the time-resolved spectral lag, are summarized as
follows. First, the evolution in the arrival offset of prompt gamma-ray photon
counts between Swift-BAT 15-25 keV and 50-100 keV energy bands (intrinsic
gamma-ray spectral lag) appears to be anti-correlated with the arrival offset
between prompt 15-350 keV gamma-rays and the optical emission observed by
TORTORA (extrinsic optical/gamma-ray spectral lag), thus effectively
partitioning the burst into two main episodes at ~T+28+/-2 sec. Second, the
rise and decline of prompt optical emission at ~T+10+/-1 sec and ~T+50+/-1 sec,
respectively, both coincide with discontinuities in the hard to soft evolution
of the photon index for a power law fit to 15-150 keV Swift-BAT data at
~T+8+/-2 sec and ~T+48+/-1 sec. These spectral energy changes also coincide
with intervals whose time-resolved spectral lag values are consistent with
zero, at ~T+12+/-2 sec and ~T+50+/-2 sec. These results, which are robust
across heuristic permutations of Swift-BAT energy channels and varying temporal
bin resolution, have also been corroborated via independent analysis of
Konus-Wind data. This potential discovery may provide the first observational
evidence for an implicit connection between spectral lags and GRB emission
mechanisms in the context of canonical fireball phenomenology. Future work
includes exploring a subset of bursts with prompt optical emission to probe the
unique or ubiquitous nature of this result.Comment: 6 pages, 3 figures. Contributed to the Proceedings of the Sixth
Huntsville GRB Symposium. Edited by C.A. Meegan, N. Gehrels, and C.
Kouvelioto
Coincident GRB neutrino flux predictions: Implications for experimental UHE neutrino physics
In the hadronic fireball phenomenology of Gamma Ray Bursts (GRBs), it is
expected that the observed photons are accompanied by UHE neutrinos, which have
not been observed yet. It is one of the challenges of experimental UHE neutrino
astrophysics to look for a signal from GRBs. In this paper, the differences
between a search for a diffuse signal and an examination of a source sample
given by e.g. BATSE will be analyzed. Since redshift information is needed to
determine the correct energy spectrum, long duration bursts with redshifts from
different estimate methods will be used. We will start with an overview of the
current understanding of GRB neutrino physics and will then use this knowledge
to make predictions for a coincidence flux and a corresponding diffuse flux. It
can be shown that shape and normalization of the spectrum is highly dependent
on the set of bursts used and that individual bursts can determine the total
spectrum.Comment: submitted to Astroparticle Physic
- âŠ