832 research outputs found
The Burst Alert Telescope (BAT) on the Swift MIDEX Mission
The Burst Alert Telescope (BAT) is one of 3 instruments on the Swift MIDEX
spacecraft to study gamma-ray bursts (GRBs). The BAT first detects the GRB and
localizes the burst direction to an accuracy of 1-4 arcmin within 20 sec after
the start of the event. The GRB trigger initiates an autonomous spacecraft slew
to point the two narrow field-of-view (FOV) instruments at the burst location
within 20-70 sec so to make follow-up x-ray and optical observations. The BAT
is a wide-FOV, coded-aperture instrument with a CdZnTe detector plane. The
detector plane is composed of 32,768 pieces of CdZnTe (4x4x2mm), and the
coded-aperture mask is composed of approximately 52,000 pieces of lead
(5x5x1mm) with a 1-m separation between mask and detector plane. The BAT
operates over the 15-150 keV energy range with approximately 7 keV resolution,
a sensitivity of approximately 10E-8 erg*cm^-2*s^-1, and a 1.4 sr (half-coded)
FOV. We expect to detect >100 GRBs/yr for a 2-year mission. The BAT also
performs an all-sky hard x-ray survey with a sensitivity of approximately 2
mCrab (systematic limit) and it serves as a hard x-ray transient monitor.Comment: 18 Pages, 12 Figures, To be published in Space Science Review
Precipitating Electrons: Evidence For Effects On Mesospheric Odd Nitrogen
Observations of electron fluxes made by the PET and LICA instruments aboard SAMPEX have been used with NO measurements made by HALOE aboard UARS to provide evidence of mesospheric and lower thermospheric NO formation due to precipitating electrons. Results indicate significant NO increases from 70 to 120 km which are associated with the occurrence of enhanced electron populations in the outer trapping regions of the magnetosphere, 2.5 ≤ L ≤ 7, which precipitate into the atmosphere
Unusual Central Engine Activity in the Double Burst GRB 110709B
The double burst, GRB 110709B, triggered Swift/BAT twice at 21:32:39 UT and 21:43:45 UT, respectively, on 9 July 2011. This is the first time we observed a GRB with two BAT triggers. In this paper, we present simultaneous Swift and Konus-WIND observations of this unusual GRB and its afterglow. If the two events are from the same physical origin, their different time-dependent spectral evolution suggest they must belong to different episodes of the central engine, which may be a magnetar-to-BH accretion system
Nonthermal Hard X-ray Emission and Iron Kalpha Emission from a Superflare on II Pegasi
We report on an X-ray flare detected on the active binary system II~Pegasi
with the Swift telescope. The trigger had a 10-200 keV luminosity of
2.2 erg s-- a superflare, by comparison with energies of
typical stellar flares on active binary systems. The trigger spectrum indicates
a hot thermal plasma with T180 K. X-ray spectral analysis
from 0.8--200 keV with the X-Ray Telescope and BAT in the next two orbits
reveals evidence for a thermal component (T80 K) and Fe K 6.4
keV emission. A tail of emission out to 200 keV can be fit with either an
extremely high temperature thermal plasma (TK) or power-law
emission. Based on analogies with solar flares, we attribute the excess
continuum emission to nonthermal thick-target bremsstrahlung emission from a
population of accelerated electrons. We estimate the radiated energy from
0.01--200 keV to be erg, the total radiated energy over
all wavelengths erg, the energy in nonthermal electrons above 20
keV erg, and conducted energy erg. The
nonthermal interpretation gives a reasonable value for the total energy in
electrons 20 keV when compared to the upper and lower bounds on the thermal
energy content of the flare. This marks the first occasion in which evidence
exists for nonthermal hard X-ray emission from a stellar flare. We investigate
the emission mechanism responsible for producing the 6.4 keV feature, and find
that collisional ionization from nonthermal electrons appears to be more
plausible than the photoionization mechanism usually invoked on the Sun and
pre-main sequence stars.Comment: 41 pages, 7 figures, accepted for publication in the Astrophysical
Journa
A 2-D Model Simulation of Downward Transport of NO_y into the Stratosphere: Effects on the 1994 Austral Spring O_3 and NO_y
Simulations using SAMPEX and HALOE data suggest that NO_y produced by thermospheric processes and by relativistic electron precipitation in the mesosphere and lower thermosphere have been important to stratospheric NO_y and O_3 during the austral spring in 1994. The relative importance of the two NO_y sources is discussed. The results are supported by an analysis of HALOE NO_x and CH_4 data during October 1994 and are in agreement with ATMOS NO_y observations made in November 1994
Unusual Central Engine Activity in the Double Burst GRB 110709B
The double burst, GRB 110709B, triggered Swift/BAT twice at 21:32:39 UT and
21:43:45 UT, respectively, on 9 July 2011. This is the first time we observed a
GRB with two BAT triggers. In this paper, we present simultaneous Swift and
Konus-WIND observations of this unusual GRB and its afterglow. If the two
events originated from the same physical progenitor, their different
time-dependent spectral evolution suggests they must belong to different
episodes of the central engine, which may be a magnetar-to-BH accretion system.Comment: 10 pages, 14 figures, 2 tables. ApJ accepte
GRB 090417B and its Host Galaxy: A Step Towards an Understanding of Optically-Dark Gamma-Ray Bursts
GRB 090417B was an unusually long burst with a T_90 duration of at least 2130
s and a multi-peaked light curve at energies of 15-150 keV. It was optically
dark and has been associated with a bright star-forming galaxy at a redshift of
0.345 that is broadly similar to the Milky Way. This is one of the few cases
where a host galaxy has been clearly identified for a dark gamma-ray burst and
thus an ideal candidate for studying the origin of dark bursts. We find that
the dark nature of GRB 090417B cannot be explained by high redshift, incomplete
observations, or unusual physics in the production of the afterglow. Assuming
the standard relativistic fireball model for the afterglow we find that the
optical flux is at least 2.5 mag fainter than predicted by the X-ray flux. The
Swift/XRT X -ray data are consistent with the afterglow being obscured by a
dense, localized sheet of dust approximately 30-80 pc from the burst along the
line of sight. Our results suggest that this dust sheet imparts an extinction
of A_V >~ 12 mag, which is sufficient to explain the missing optical flux. GRB
090417B is an example of a gamma-ray burst that is dark due to the localized
dust structure in its host galaxy.Comment: Accepted for publication in Ap
Post-mortem volatiles of vertebrate tissue
Volatile emission during vertebrate decay is a complex process that is understood incompletely. It depends on many factors. The main factor is the metabolism of the microbial species present inside and on the vertebrate. In this review, we combine the results from studies on volatile organic compounds (VOCs) detected during this decay process and those on the biochemical formation of VOCs in order to improve our understanding of the decay process. Micro-organisms are the main producers of VOCs, which are by- or end-products of microbial metabolism. Many microbes are already present inside and on a vertebrate, and these can initiate microbial decay. In addition, micro-organisms from the environment colonize the cadaver. The composition of microbial communities is complex, and communities of different species interact with each other in succession. In comparison to the complexity of the decay process, the resulting volatile pattern does show some consistency. Therefore, the possibility of an existence of a time-dependent core volatile pattern, which could be used for applications in areas such as forensics or food science, is discussed. Possible microbial interactions that might alter the process of decay are highlighted
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