38 research outputs found
HETE-II and the Interplanetary Network
The FREGATE experiment aboard HETE-II has been successfully integrated into
the Third Interplanetary Network (IPN) of gamma-ray burst detectors. We show
how HETE's timing has been verified in flight, and discuss what HETE can do for
the IPN and vice-versa.Comment: To appear in the proceedings of the conference on Gamma-Ray Burst and
Afterglow Astronomy 2001: A Workshop Celebrating the First Year of the HETE
Mission, to be published by AIP. Figures must be downloaded and printed
separatel
Development of an XSPEC-Based Spectral Analysis System for the Coded-Aperture Hard X-ray Balloon Payload EXITE2
We present the spectral analysis system for the second-generation Energetic
X-ray Imaging Telescope Experiment (EXITE2) balloon payload. EXITE2 is an
imaging hard X-ray telescope using a coded-aperture mask and a NaI/CsI phoswich
detector operating in the energy range 20--600 keV. The instrument was flown on
a high-altitude scientific balloon from Ft. Sumner, NM on 1997 May 7-8. We
describe the details of the EXITE2 spectral analysis system, with emphasis on
those aspects peculiar to coded-aperture instruments. In particular, we have
made our analysis compatible with the standard X-ray spectral fitting package
XSPEC by generating a response matrix in the appropriate format including all
the effects of a coded-aperture system. The use of XSPEC, which may be a first
for coded-aperture data, permits great flexibility in the fitting of spectral
models. The additional effects of our phoswich system, or any other
detector-specific considerations, may be easily included as well. We test our
spectral analysis using observations of the Crab Nebula, and find that the
EXITE2 Crab spectrum is consistent with those recorded by previous instruments
operating in this energy range.Comment: 17 pages LaTeX, 6 figures, accepted to Astroparticle Physic
Global Characteristics of X-Ray Flashes and X-Ray-Rich GRBs Observed by HETE-2
We describe and discuss the global properties of 45 gamma-ray bursts (GRBs)
observed by HETE-2 during the first three years of its mission, focusing on the
properties of X-Ray Flashes (XRFs) and X-ray-rich GRBs (XRRs). We find that the
numbers of XRFs, XRRs, and GRBs are comparable. We find that the durations and
the sky distributions of XRFs and XRRs are similar to those of GRBs. We also
find that the spectral properties of XRFs and XRRs are similar to those of
GRBs, except that the values of the peak energy of the
burst spectrum in , the peak energy flux \Fp, and the energy
fluence of XRFs are much smaller -- and those of XRRs are smaller -- than
those of GRBs. Finally, we find that the distributions of all three kinds of
bursts form a continuum in the [(2-30 keV),(30-400) keV]-plane, the
[(2-400 keV), ]-plane, and the [(50-300 keV),
]-plane. These results provide strong evidence that all three
kinds of bursts arise from the same phenomenon.Comment: 33 pages, 15 figures, submitted to Ap
Spectral analysis of 35 GRBs/XRFs observed with HETE-2/FREGATE
We present a spectral analysis of 35 GRBs detected with the HETE-2 gamma-ray
detectors (the FREGATE instrument) in the energy range 7-400 keV. The GRB
sample analyzed is made of GRBs localized with the Wide Field X-ray Monitor
onboard HETE-2 or with the GRB Interplanetary Network. We derive the spectral
parameters of the time-integrated spectra, and present the distribution of the
low-energy photon index, alpha, and of the peak energy, e_peak . We then
discuss the existence and nature of the recently discovered X-Ray Flashes and
their relationship with classical GRBs.Comment: 14 pages, 43 figures, accepted for publication in Astronomy and
Astrophysic
Scientific Highlights of the HETE-2 Mission
The HETE-2 mission has been highly productive. It has observed more than 250
GRBs so far. It is currently localizing 25 - 30 GRBs per year, and has
localized 43 GRBs to date. Twenty-one of these localizations have led to the
detection of X-ray, optical, or radio afterglows, and as of now, 11 of the
bursts with afterglows have known redshifts. HETE-2 has confirmed the
connection between GRBs and Type Ic supernovae, a singular achievement and
certainly one of the scientific highlights of the mission so far. It has
provided evidence that the isotropic-equivalent energies and luminosities of
GRBs are correlated with redshift, implying that GRBs and their progenitors
evolve strongly with redshift. Both of these results have profound implications
for the nature of GRB progenitors and for the use of GRBs as a probe of
cosmology and the early universe. HETE-2 has placed severe constraints on any
X-ray or optical afterglow of a short GRB. It is also solving the mystery of
"optically dark' GRBs, and revealing the nature of X-ray flashes.Comment: 10 pages, 9 figures, to appear in proc. "The Restless High-Energy
Universe", Royal Tropical Institute, Amsterdam; revised text, added ref
The QMAP and MAT/TOCO Experiments for Measuring Anisotropy in the Cosmic Microwave Background
We describe two related experiments that measured the anisotropy in the
cosmic microwave background (CMB). QMAP was a balloon-borne telescope that flew
twice in 1996, collecting data on degree angular scales with an array of six
high electron mobility transistor-based amplifiers (HEMTs). QMAP was the first
experiment to use an interlocking scan strategy to directly produce high
signal-to-noise CMB maps. The QMAP gondola was then refit for ground based work
as the MAT/TOCO experiment. Observations were made from 5200 m on Cerro Toco in
Northern Chile in 1997 and 1998 using time-domain beam synthesis. MAT/TOCO was
the first experiment to see both the rise and fall of the CMB angular spectrum,
thereby localizing the position of the first peak to l_{peak}=216 +/- 14. In
addition to describing the instruments, we discuss the data selection methods,
checks for systematic errors, and we compare the MAT/TOCO results to those from
recent experiments. We also correct the data to account for an updated
calibration and a small contribution from foreground emission. We find the
amplitude of the first peak for l between 160 and 240 to be T_{peak}=80.9 +/-
3.4 +/- 5.1 uK, where the first error is statistical and the second is from
calibration.Comment: 31 pages, 11 figures, Submitted to Ap
HETE-2 Localization and Observation of the Bright, X-Ray-Rich Gamma-Ray Burst GRB021211
A bright, x-ray-rich GRB was detected by HETE-2 at 11:18:34.03 UT on 11 Dec
2002. The WXM localization was to 14' and relayed to the GCN 22 s after the
start of the burst. The ground SXC localization was within 2' of R.A. 08h 09m
00s, Dec 06d 44' 20" (J2000). GRB021211 consists of a single, FRED-like pulse
with t90s of 2.3 s (85-400 keV) and 8.5 s (2-10 keV). The peak photon number
and photon energy fluxes in the 2-400 keV band, are 34.0 +/- 1.8 ph cm^-2 s^-1
and 1.68 +/- 0.11 x 10^-6 erg cm^-2 s^-1, respectively. The energy fluences in
the 2-30 keV and 30-400 kev energy bands are S_X = 1.36 +/- 0.05 x 10^-6 erg
cm^-2 and S_gamma 2.17 +/- 0.15 x 10^-6 erg cm^-2, respectively. Thus GRB021211
is an X-ray-rich GRB (S_X/S_gamma = 0.63 > 0.32). The spectrum is well-fit by a
Band function (alpha = -0.805, beta = -2.37, E_peak = 46.8 keV). The prompt
localization allowed the detection of an optical afterglow for what would
otherwise have been an ``optically dark'' GRB. GRB 021211 demonstrates that
some fraction of burst afterglows are ``optically dark'' because their optical
afterglows at times > 1 hr after the burst are very faint, and thus have often
escaped detection. GRB 021211 shows that such ``optically dim'' bursts can have
very bright afterglows at times < 20 min after the burst.Comment: 21 pages, 4 figures, accepted by ApJ, abstract. condensed; revise
Aripiprazole Augmentation in the Treatment of Military-Related PTSD with Major Depression: a retrospective chart review
<p>Abstract</p> <p>Background</p> <p>In this chart review, we attempted to evaluate the benefits of adding aripiprazole in veterans with military-related PTSD and comorbid depression, who had been minimally or partially responsive to their existing medications.</p> <p>Methods</p> <p>A retrospective chart review of patients who received an open-label, flexible-dose, 12- week course of adjunctive aripiprazole was conducted in 27 military veterans meeting DSM-IV criteria for PTSD and comorbid major depression. Concomitant psychiatric medications continued unchanged, except for other antipsychotics which were discontinued prior to initiating aripiprazole. The primary outcome variable was a change from baseline in the PTSD checklist-military version (PCL-M) and the Beck Depression Inventory (BDI-II).</p> <p>Results</p> <p>PTSD severity (Total PCL scores) decreased from 56.11 at baseline to 46.85 at 12-weeks (p < 0.0001 from Wilcoxon signed rank test) and the depression severity decreased from 30.44 at baseline to 20.67 at 12-weeks (p < 0.0001 from Wilcoxon signed rank test). Thirty seven percent (10/27) were considered responders, as defined by a decrease in total PCL scores of at least 20 percent and 19% (5/27) were considered as responders as defined by a decrease in total BDI score of at least 50%.</p> <p>Conclusions</p> <p>The addition of aripiprazole contributed to a reduction in both PTSD and depression symptomatology in a population that has traditionally demonstrated poor pharmacological response. Further investigations, including double-blind, placebo-controlled studies, are essential to confirm and further demonstrate the benefit of aripiprazole augmentation in the treatment of military related PTSD.</p