1,774 research outputs found
Event reconstruction in high resolution Compton telescopes
The development of germanium Compton telescopes for nuclear gamma-ray
astrophysics (~0.2-20 MeV) requires new event reconstruction techniques to
accurately determine the initial direction and energy of photon events, as well
as to consistently reject background events. This paper describes techniques
for event reconstruction, accounting for realistic instrument/detector
performance and uncertainties. An especially important technique is Compton
Kinematic Discrimination, which allows proper interaction ordering and
background rejection with high probabilities. The use of these techniques are
crucial for the realistic evaluation of the performance and sensitivity of any
germanium Compton telescope configuration.Comment: Accepted for publication in A&AS
Searching for annihilation radiation from SN 1006 with SPI on INTEGRAL
Historical Type Ia supernovae are a leading candidate for the source of
positrons observed through their diffuse annihilation emission in the Galaxy.
However, search for annihilation emission from individual Type Ia supernovae
has not been possible before the improved sensitivity of \integral. The total
511 keV annihilation flux from individual SNe Ia, as well as their contribution
to the overall diffuse emission, depends critically on the escape fraction of
positrons produced in Co decays. Late optical light curves suggest that
this fraction may be as high as 5%. We searched for positron annihilation
radiation from the historical Type Ia supernova SN 1006 using the SPI
instrument on \integral. We did not detect significant 511 keV line emission,
with a 3 flux upper limit of 0.59 x 10 ergs cm^-2 s^-1 for \wsim
1 Msec exposure time, assuming a FWHM of 2.5 keV. This upper limit corresponds
to a 7.5% escape fraction, 50% higher than the expected 5% escape scenario, and
rules out the possibility that Type Ia supernovae produce all of the positrons
in the Galaxy (~ 12% escape fraction), if the mean positron lifetime is less
than 10 years. Future observations with \integral will provide stronger
limits on the escape fraction of positrons, the mean positron lifetime, and the
contribution of Type Ia supernovae to the overall positron content of the
Galaxy.Comment: 3 pages, 2 figures, accepted for publication in ApJ
Correspondence to General William Robertson Boggs, 1890s: March 7, 1892 - October 1, 1899.
Boggs Family Papers, Box 1, Folder 5.
Correspondence to General William Robertson Boggs, 1890s: March 7, 1892 - October 1, 1899.https://digitalcommons.wofford.edu/littlejohnboggs/1004/thumbnail.jp
Diffuse Galactic Soft Gamma-Ray Emission
The Galactic diffuse soft gamma-ray (30-800 keV) emission has been measured
from the Galactic Center by the HIREGS balloon-borne germanium spectrometer to
determine the spectral characteristics and origin of the emission. The
resulting Galactic diffuse continuum is found to agree well with a single
power-law (plus positronium) over the entire energy range, consistent with RXTE
and COMPTEL/CGRO observations at lower and higher energies, respectively. We
find no evidence of spectral steepening below 200 keV, as has been reported in
previous observations. The spatial distribution along the Galactic ridge is
found to be nearly flat, with upper limits set on the longitudinal gradient,
and with no evidence of an edge in the observed region. The soft gamma-ray
diffuse spectrum is well modeled by inverse Compton scattering of interstellar
radiation off of cosmic-ray electrons, minimizing the need to invoke
inefficient nonthermal bremsstrahlung emission. The resulting power requirement
is well within that provided by Galactic supernovae. We speculate that the
measured spectrum provides the first direct constraints on the cosmic-ray
electron spectrum below 300 MeV.Comment: 26 pages, 7 figure, submitted to Ap
Spectral Analysis of GRBs Measured by RHESSI
The Ge spectrometer of the RHESSI satellite is sensitive to Gamma Ray Bursts
(GRBs) from about 40 keV up to 17 MeV, thus ideally complementing the Swift/BAT
instrument whose sensitivity decreases above 150 keV. We present preliminary
results of spectral fits of RHESSI GRB data. After describing our method, the
RHESSI results are discussed and compared with Swift and Konus.Comment: 4 pages, 4 figures, conference proceedings, 'Swift and GRBs:
Unveiling the Relativistic Universe', San Servolo, Venice, 5-9 June 2006, to
appear in Il Nouvo Ciment
Use of a pulsed laser to study properties of CdZnTe pixel detectors
We have investigated the utility of employing a short (<4 ns) pulsed laser with wavelength tunable between 600 - 950 nm as a tool for studying and characterizing CdZnTe detectors. By using a single mode optical fiber and simple optics, we can focus the beam to a spot size of less than 10 micrometers and generate the number of the excess carriers equivalent to a several MeV gamma-ray either at the surface or deep inside the sample. The advantages of this technique over use of a collimated X-ray or alpha particle source are strong induced signal, precise pointing, and triggering capability. As examples of using this technique, we present the results of measurements of the drift velocity, electron lifetime, and electric field line distribution inside CZT pixel detectors
Search for polarization from the prompt gamma-ray emission of GRB 041219a with SPI on INTEGRAL
Measuring the polarization of the prompt gamma-ray emission from GRBs can significantly improve our understanding of both the GRB emission mechanisms, as well as the underlying engine driving the explosion. We searched for polarization in the prompt gamma-ray emission of GRB 041219a with the SPI instrument on INTEGRAL. Using multiple-detector coincidence events in the 100--350 keV energy band, our analysis yields a polarization fraction from this GRB of 99 +- 33 %. Statistically, we cannot claim a polarization detection from this source. Moreover, different event selection criteria lead to even less significant polarization fractions, e.g. lower polarization fractions are obtained when higher energies are included in the analysis. We cannot strongly rule out the possibility that the measured modulation is dominated by instrumental systematics. Therefore, SPI observations of GRB 041219a do not significantly constrain GRB models. However, this measurement demonstrates the capability of SPI to measure polarization, and the techniques developed for this analysis
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