115 Matching Results

Search Results

Advanced search parameters have been applied.

in subjects: "Cosmic Gamma Bursts"

open access

3-10 keV and 0. 1- to 2-MeV observations of four gamma-ray bursts

Four catalogued ..gamma..-ray bursts that occurred between 79/3/7 and 79/7/31 have been observed over the 3 to 10 keV range by a joint NRL/Los Alamos experiment on the Air Force P78-1 satellite. The bursts were also well observed by members of the interplanetary network. In this paper we present hardness ratios, x-ray/..gamma..-ray luminosity ratios, and time histories. The most significant results presented herein can be summarized as follows: (1) gamma-ray bursters can emit fairly strongly at… more

Date: January 1, 1983

Creator: Laros, J. G.; Evans, W. D.; Fenimore, E. E.; Klebesadel, R. W.; Shulman, S. & Fritz, G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Afterglow Radiation from Gamma Ray Bursts

Gamma-ray bursts (GRB) are huge fluxes of gamma rays that appear randomly in the sky about once a day. It is now commonly accepted that GRBs are caused by a stellar object shooting off a powerful plasma jet along its rotation axis. After the initial outburst of gamma rays, a lower intensity radiation remains, called the afterglow. Using the data from a hydrodynamical numerical simulation that models the dynamics of the jet, we calculated the expected light curve of the afterglow radiation that … more

Date: August 28, 2006

Creator: Desmond, Hugh & /SLAC, /Leuven U.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Analysis of gamma-ray burst energy spectra

This report summarizes the work carried out under LLNL Contract Number B108527, subcontracted by the Regents of the University of California at Berkeley. The research carried out under this contract includes assisting in the data analysis for the Prognoz-9 mission, linking results of the computer codes to the Prognoz-9 data library in order to study the spectral shape and evolution of cosmic gamma-ray burst energy spectra, and using the results of this study to help to determine or constrain th… more

Date: January 1, 1990

Creator: Hurley, K. (California Univ., Berkeley, CA (USA). Space Sciences Lab.)

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Analysis of gamma ray burst spectra with cyclotron lines

Motivated by the recent developments in the cyclotron resonance upscattering of soft photons or CUSP model of Gamma Ray Burst (GRB) continuum spectra, we revisit a select database of GRBs with credible cyclotron absorption features. We measure the break energy of the continuum, the slope below the break and deduce the soft photon energy or the electron beam Lorentz factor cutoff. We study the correlation (or lack of) between various parameters in the context of the CUSP model. One surprise resu… more

Date: September 26, 1990

Creator: Kargatis, V. (Rice Univ., Houston, TX (USA). Dept. of Space Physics and Astronomy) & Liang, E.P. (Lawrence Livermore National Lab., CA (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Astronomy at Ultra-High Energies: Results From the CYGNUS Experiment

The CYGNUS experiment is composed of an air-shower array and muon detectors, located in Los Alamos, NM, and operating at energies above 50 TeV. Recent results include a search for emission from Cygnus X-3 during the radio outbursts of June and July 1989, preliminary results from a search for diffuse emission from the galactic plane, and preliminary results from a search for emission from possible northern hemisphere point sources, both known and unknown. 3 refs., 4 figs.

Date: January 1, 1990

Creator: Alexandreas, D. E.; Allen, R. C.; Biller, S. D.; Dion, G. M.; Lu, X-Q.; Vishwanath, P. R. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

BATSE burst location accuracy and constraints on the fraction of repeating GRB sources

We use a one parameter model for GRB source repetition to investigate the ability of BATSE to detect source repetition and to place constraints on the fraction of repeating sources. From Monte Carlo simulations we find that the current uncertainty in BATSE burst locations severely limits our ability to confidently detect source repetition from distributions containing fewer than 10 {minus}15% repeaters. A fit of our repetition model to 260 BATSE catalog bursts yields a best-fit repeating fracti… more

Date: December 31, 1993

Creator: Strohmayer, T. E.; Fenimore, E. E. & Miralles, J. A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Binary neutron star GRB model

In this paper we present the preliminary results of a model for the production of gamma-ray bursts (GRBs) through the compressional heating of binary neutron stars near their last stable orbit prior to merger. Recent numerical studies of the general relativistic (GR) hydrodynamics in three spatial dimensions of close neutron star binaries (NSBs) have uncovered evidence for the compression and heating of the individual neutron stars (NSs) prior to merger. This effect will have significant effect… more

Date: November 11, 1997

Creator: Wilson, J. R.; Salmonson, J. D. & Mathews, G. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Burstman: a portable GRB detector for really long voyages

The renewal of the Ulysses mission to the year 2001, and the failure of Mars Observer, once more leave the Interplanetary Network with only two widely spaced components. We have therefore developed and begun to build a small GRB detector for the Russian Mars `96 mission. A prototype has now been delivered to Russia for spacecraft tests. Three interesting features of this experiment are first, that it measures both particles and gamma rays, second, that it is not much larger than a Walkman (henc… more

Date: October 1, 1995

Creator: Hurley, K.; Primbsch, J.H. & Berg, P.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The Case for Anisotropic Afterglow Efficiency Within Gamma-Ray Burst Jets

Early X-ray afterglows recently detected by Swift frequently show a phase of very shallow flux decay lasting from a few hundred seconds up to {approx} 10{sup 4} s, followed by a steeper, more familiar decay. We suggest that the flat early part of the light curve may be a combination of the decaying tail of the prompt emission and the delayed onset of the afterglow emission observed from viewing angles slightly outside the edge of the jet, as predicted previously. This would imply that a signifi… more

Date: October 5, 2005

Creator: Eichler, David; Negev, /Ben Gurion U. of; Granot, Jonathan & /KIPAC, Menlo Park

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Collimated Jet Or Expanding Outflow: Possible Origins of GRBs And X-Ray Flashes

We investigate the dynamics of an injected outflow propagating in a progenitor in the context of the collapsar model for gamma-ray bursts (GRBs) through two dimensional axisymmetric relativistic hydrodynamic simulations. Initially, we locally inject an outflow near the center of a progenitor. We calculate 25 models, in total, by fixing its total input energy to be 10{sup 51} ergs s{sup -1} and radius of the injected outflow to be 7 x 10{sup 7} cm while varying its bulk Lorentz factor, {Lambda}{… more

Date: August 10, 2006

Creator: Mizuta, Akira; /Kyoto U., Yukawa Inst., Kyoto /Garching, Max Planck Inst.; Yamasaki, Tatsuya; /Kyoto U., Yukawa Inst., Kyoto; Nagataki, Shigehiro; /Kyoto U., Yukawa Inst., Kyoto /KIPAC, Menlo Park et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Constraints on Short Gamma-Ray Burst Models with Optical Limits of GRB 050509b

We have obtained deep optical images with the Very Large Telescope at ESO of the first well-localized short-duration gamma-ray burst, GRB 050509b. We observed in the V and R bands at epochs starting at {approx}2 days after the GRB trigger and lasting up to three weeks. We detect no variable objects inside the small Swift/XRT X-ray error circle down to 5{sigma} limiting magnitudes of V = 26.5 and R = 25.2. The X-ray error circle includes a giant elliptical galaxy at z = 0.225, which has been pro… more

Date: June 15, 2005

Creator: Hjorth, Jens; Sollerman, J.; Gorosabel, J.; Granot, J.; Klose, S.; Kouveliotou, C. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

A continuous watch of the northern sky above 40 TeV with the CYGNUS array

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). The aim of the project has been to continuously monitor the northern sky for transient high-energy gamma-ray emission from astrophysical sources. Potential objects of such emission include gamma-ray bursts and flares from active galaxies. At the start of this project, the CYGNUS extensive air shower array was used for the monitoring; CYGNUS has an e… more

Date: November 1, 1998

Creator: Haines, T.J.; Miller, R. & Sinnis, C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Continuum spectra for gamma-ray bursts: Suppressing the soft photons

Gamma-ray bursts are observed to have very steep spectra below photon energy /approximately/100 keV; some have photon number spectra as steep as F /proportional to/ E/sup 0/. This property has been difficult to explain in terms of most radiation processes. The BATSE experiment on the Gamma Ray Observatory should be able to test how common this spectral property is and whether there are bursts with even steeper low-energy spectra. To explain this spectral steepness, we study a model in which the… more

Date: January 1, 1989

Creator: Ho, Cheng & Epstein, R. I.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Cosmic gamma-ray bursts: a review of the observational data

No Description Available.

Date: January 1, 1974

Creator: Strong, I.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Cosmological gamma-ray bursts

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Gamma-ray bursts are brief events that dominate the emission from all other gamma-ray objects in the sky, flicker for tens of seconds, and then turn off. Their nature remains uncertain despite years of efforts to understand them. One hypothesis is that the bursts arise within our galaxy albeit in an extended halo of neutron stars. Another hypothesis… more

Date: April 1, 1996

Creator: Fenimore, E.; Epstein, R.; Ho, C. & Intzand, J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Detection of 10/sup 14/-eV Gamma Rays from Cygnus X-3 during 1986

Cosmic ray muons associated with extensive air showers were detected by a scintillator array. Data were collected within a 30 degree cone centered about the zenith. About 20,000 showers per day were recorded. 5 refs., 4 figs.

Date: January 1, 1987

Creator: Nagle, D. E.; Bolton, R. D.; Burman, R. L.; Butterfield, K. B.; Cady, R.; Carlini, R. D. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Distribution of Gamma-ray Burst Ejecta Energy with Lorentz Factor

The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time (F{sub {nu}} {proportional_to} t{sup -{alpha}} with 0.2 {approx}< {alpha} {approx}< 0.8) for 10{sup 2.5} s{approx}< t {approx}< 10{sup 4} s, while the subsequent decline is the usual 1 {approx}< {alpha}{sub 3} {approx}< 1.5 behavior, that was seen in the pre-Swift era. We show that this behavior is a natural cons… more

Date: October 7, 2005

Creator: Granot, Jonathan & Kumar, Pawan

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

DMSP satellite detections of gamma-ray bursts

Gamma-ray burst detectors are aboard six U. S. Air Force defense Meteorological Satellite Program (DMSP) spacecraft, two of which are currently in use. Their 800-km altitude orbits give a field of view to 117 degrees from the zenith. A great many bursts have been detected, usually in coincidence with detections by GRO or other satellites such as PVO or ULYSSES. The directions of the sources can be determined with considerable accuracy from such correlated observations, even when GRO/BATSE with … more

Date: December 31, 1995

Creator: Terrell, J.; Lee, P. & Klebesadel, R.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

DMSP satellites as gamma-ray burst detectors

Gamma-ray burst detectors are aboard three US Air Force Defense Meteorological Satellite Program (DMSP) spacecraft, in orbit at 800 km altitude, with corresponding fields of view to 117{degree} from the zenith. A large number of bursts have been detected by DMSP, usually confirming and supplementing data from GRO and other spacecraft. The location of a gamma-ray burst source detected by several DMSP spacecraft is considerably restricted by knowledge of the several fields of view. Often non-dete… more

Date: December 31, 1993

Creator: Terrell, J.; Lee, P.; Klebesadel, R. W. & Griffee, J. W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Emission region of gamma ray bursts

Within the last few years the rapid accumulation of gamma ray burst spectral data, especially those of KONUS and SMM, has made the confrontation between theories of the gamma ray emission mechanisms and observations much more urgent and challenging. At present the most viable model seems to be some combination of inverse Comptonization and synchrotron emission. In this paper we limit the acceptable parameter space of the emission region by taking into account the maximum set of observational co… more

Date: May 1, 1985

Creator: Liang, E.P.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

THE ENERGY DISTRIBUTION OF GRBs

No Description Available.

Date: January 1, 2000

Creator: Piran, T.; Jimenez, R. & Band, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The escape of > MeV photons from cosmological gamma-ray bursts

The recent BATSE result indicates that gamma-ray bursts may be at cosmological distances. AS such one must reconcile the high photon densities with the observations of spectra to energies well above the pair production threshold. We have investigated two models of relativistic flows that could provide the requiste beaming to allow the escape of 100 MeV photons: a stationary relativistic wind with a photosphere and a relativistic expanding shell. For typical cosmological gamma-ray burst paramete… more

Date: January 1, 1992

Creator: Fenimore, E. E.; Epstein, R. I. & Ho, C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The escape of > MeV photons from cosmological gamma-ray bursts

Date: June 1, 1992

Creator: Fenimore, E. E.; Epstein, R. I. & Ho, C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The expected rates of X-ray flashes from GRBs in ROSAT and preliminary search results

The recent long (up to days) and relatively bright soft X-ray afterglows from GRBs detected by BeppoSAX raise the possibility of detecting similar events in the ROSAT database. The authors perform detailed calculations on the expected number of ROSAT events based on the extended halo scenario. They use the realistic ROSAT capabilities and the actual exposure time on bright nearby galaxies. They find that the expected number of x-ray events is quite low, {approximately} 1, and depends on the pea… more

Date: December 1, 1998

Creator: Li, H.; Sun, X. & Fenimore, E.E.

Item Type: Article

Partner: UNT Libraries Government Documents Department