981 research outputs found
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
The BATSE experiment on the Compton Gamma Ray Observatory: Status and some early results
The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO) is a sensitive all-sky detector system. It consists of eight uncollimated detectors at the corners of the spacecraft which have a total energy range of 15 keV to 100 MeV. The primary objective of BATSE is the detection, location, and study of gamma ray bursts and other transient sources. The instrement also has considerable capability for the study of pulsars, solar flares, and other discrete high energy sources. The experiment is now in full operation, detecting about one gamma ray burst per day. A brief description of the on-orbit performance of BATSE is presented, along with examples of early results from some of the gamma ray bursts
The BATSE Gamma-Ray Burst Spectral Catalog. I. High Time Resolution Spectroscopy of Bright Bursts using High Energy Resolution Data
This is the first in a series of gamma-ray burst spectroscopy catalogs from
the Burst And Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory, each covering a different aspect of burst phenomenology. In this
paper, we present time-sequences of spectral fit parameters for 156 bursts
selected for either their high peak flux or fluence. All bursts have at least
eight spectra in excess of 45 sigma above background and span burst durations
from 1.66 to 278 s. Individual spectral accumulations are typically 128 ms long
at the peak of the brightest events, but can be as short as 16 ms, depending on
the type of data selected. We have used mostly high energy resolution data from
the Large Area Detectors, covering an energy range of typically 28 - 1800 keV.
The spectral model chosen is from a small empirically-determined set of
functions, such as the well-known `GRB' function, that best fits the
time-averaged burst spectra. Thus, there are generally three spectral shape
parameters available for each of the 5500 total spectra: a low-energy power-law
index, a characteristic break energy and possibly a high-energy power-law
index. We present the distributions of the observed sets of these parameters
and comment on their implications. The complete set of data that accompanies
this paper is necessarily large, and thus is archived electronically at:
http://www.journals.uchicago.edu/ApJ/journal/.Comment: Accepted for publication: ApJS, 125. 38 pages, 9 figures;
supplementary electronic archive to be published by ApJ; available from lead
author upon reques
The Interstellar Medium toward the Galactic Center Source 2MASS J17470898-2829561
We describe and discuss remarkable infrared spectra, covering key portions of
the m wavelength interval, of the probable OH/IR supergiant 2MASS
J174708982829561 (2M1747), located in direction of the Sgr B molecular cloud
complex within the Central Molecular Zone (CMZ) of the Galaxy. This star was
originally singled out for examination based on its suitability for
spectroscopy of lines of H in the CMZ. Analysis of the spectra shows that
2M1747 is deeply embedded within Sgr B1, with A 100 mag, making
it the only star within Sgr B for which infrared spectra have been obtained at
present, and thereby a unique infrared probe of the dense interstellar medium
within the CMZ. Despite the high extinction, spectra of 2M1747 reveal a veiled
photosphere in the band and circumstellar gas in the band, giving clues
as to its nature. Its m spectrum contains the strongest
absorption lines of H observed toward any object to date. The
m spectrum has impressively deep and wide absorption lines of interstellar
CO, most of which arise in dense gas within Sgr B1. The m spectrum
also contains several solid state absorption features, which are characteristic
of both dense and diffuse clouds, and which raise questions about the
identifications of some of these features. We discuss the nature of the star,
the extinction to it, the extinction law for dust in the CMZ, and the
identifications of the various solid-state features and where they are produced
along this complex line of sight.Comment: 17 pages, 10 figures; accepted by ApJ 2021 March 1
Mesospheric Planetary Waves atNorthern Hemisphere Fall Equinox
Northern hemisphere planetary waves are strong in the winter and weak in the summer, and they go through a fast transition around equinox. This transition is studied here using NCAR Thermosphere‐Ionosphere‐Mesosphere‐Electrodynamics general circulation model (TIME‐GCM) simulations with 1997 National Centers for Environmental Prediction (NCEP) analysis. The planetary wave variability during the transition and its effect on the temperature and winds in the mesosphere are examined. The simulated planetary wave structure agrees with climatological studies, and the fast transition of the planetary waves is captured by the model. The wave variability produces large temperature changes in the upper atmosphere above local stations in middle and high latitudes. The qualitative behavior of the model is in excellent agreement with recent observations of a major perturbation in OH mesospheric temperatures from Ft. Collins (Taylor et al., 2001), although the smaller calculated magnitude suggests that the planetary wave amplitude might be underestimated by the model
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