1,187 research outputs found
Spectroscopy in the 10 keV to 10 MeV range
Spectral lines in the 10 keV to 1 MeV range carry information of fundamental importance on many astronomical objects. Since the lines are directly related to specific physical processes this information is model independent and gives the physical conditions in the objects. At the sensitivities achieved to date, approximately 0.0001 to 0.001 phsq cm. sec for steady sources and approximately 0.01 to 1 ph/sq cm sec for transient sources, lines were detected from the galactic center, gamma-ray bursts and transients, X-ray pulsators, the Crab pulsar and solar flares. Future instruments with a factor of approximately 100 sensitivity improvement will allow detailed spectroscopic study of these classes of objects as well as supernova remnants, active galaxies and the interstellar medium. This sensitivity improvement can be obtained through the use of detector technology already proven in balloon and satellite instruments
HEAO-1 observations of gamma ray bursts
A search of data from the High Energy X-Ray and Low Energy Gamma Ray Experiment on HEAO-1 uncovered 14 gamma ray bursts. Nine of these events are reported for the first tiome. Except for the faintest events, all of the bursts detected by this experiment have been measured above an MeV, thereby confirming the hard spectral character of gamma ray burst spectra reported by SMM. Results give a burst rate of at least 105 per year above 6 times 10 to the minus 7th power ergs, which is consistent with previous measurements of burst frequency
A-4 scientific results
Observations of galactic sources, extragalactic sources and gamma bursts with the A-4 instrument at energy 1 energies of between 0.1 to 10 MeV are discussed. Aximuthal scans are presented. The Crab Nebula and its spectrum and the spectrum of Cygnus Z-1 are described
The Statistics of the BATSE Spectral Features
The absence of a BATSE line detection in a gamma-ray burst spectrum during
the mission's first six years has led to a statistical analysis of the
occurrence of lines in the BATSE burst database; this statistical analysis will
still be relevant if lines are detected. We review our methodology, and present
new simulations of line detectability as a function of the line parameters. We
also discuss the calculation of the number of ``trials'' in the BATSE database,
which is necessary for our line detection criteria.Comment: 5 pages, 2 figures, AIPPROC LaTeX, to appear in "Gamma-Ray Bursts,
4th Huntsville Symposium," eds. C. Meegan, R. Preece and T. Koshu
Spectrum of the gamma-ray diffuse component observed from HEAO-1
The spectrum of the diffuse X and gamma ray background was measured between 15 keV and 4 MeV with the scintillation detectors aboard the HEAO 1 satellite. The apertures of the detectors were modulated on time scales of hours and the difference in counting rates measured the diffuse component flux. The observed spectrum is presented and compared with other measurements. At least two components are indicated, one below -100 keV and the other above. Possible origins are discussed
Spectra and positions of galactic gamma-ray sources
The UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment aboard HEAO-1 scanned the galactic center region during three epochs in 1977 and 1978 from 13 to 180 keV. The results are presented from the scanning epoch of 1978 September. Twenty-two known 2 to 10 keV source positions were necessary for an acceptable fit to the data. The spectra of the 16 strongest, least confused sources are all consistent with power laws with photon spectral indices ranging from 2.1 to 7.2. Acceptable fits to thermal bremsstrahlung models are also possible for most sources. No one source in this survey can be extrapolated to higher energy to match the intensity of the gamma-ray continuum as measured by HEAO-1 large field of view detectors, which implies that the continuum is a composite of contributions from a number of sources
Locally Adaptive Shrinkage Priors for Trends and Breaks in Count Time Series
Non-stationary count time series characterized by features such as abrupt
changes and fluctuations about the trend arise in many scientific domains
including biophysics, ecology, energy, epidemiology, and social science
domains. Current approaches for integer-valued time series lack the flexibility
to capture local transient features while more flexible models for continuous
data types are inadequate for universal applications to integer-valued
responses such as settings with small counts. We present a modeling framework,
the negative binomial Bayesian trend filter (NB-BTF), that offers an adaptive
model-based solution to capturing multiscale features with valid integer-valued
inference for trend filtering. The framework is a hierarchical Bayesian model
with a dynamic global-local shrinkage process. The flexibility of the
global-local process allows for the necessary local regularization while the
temporal dependence induces a locally smooth trend. In simulation, the NB-BTF
outperforms a number of alternative trend filtering methods. Then, we
demonstrate the method on weekly power outage frequency in Massachusetts
townships. Power outage frequency is characterized by a nominal low level with
occasional spikes. These illustrations show the estimation of a smooth,
non-stationary trend with adequate uncertainty quantification.Comment: 31 pages, 6 figure
Gamma-ray burst spectroscopy capabilities of the BATSE/GRO experiment
A scintillation spectrometer is included in each of the eight BATSE/GRO detector modules, resulting in all-sky coverage for gamma-ray bursts. The scientific motivation, design and capabilities of these spectrometers for performing spectral observations over a wide range of gamma-ray energies and burst intensities are described
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