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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Consistency of time dilation in temporal profiles and spectra of gamma-ray bursts

If gamma-ray bursters are at cosmological distances-a possibility suggested by their isotropic distribution and spatial inhomogeneity-then the temporal profiles and spectra of more distant sources will be time dilated compared to those of relatively nearby sources. Analyses of bright and dim Burst and Transient Source Experiment (BATSE) gamma-ray bursts yield a relative time-dilation factor of 2.3 on timescales of pulses and event durations. We redshift the spectra of time intervals near the intensity peaks of the bright sample on a trial grid and compare with spectra of the dim sample. A redshift factor of order two-with wide latitude permitted-brings the spectra of the two brightness groups into alignment. Thus there is coarse agreement with the time-dilation factor found in the temporal domain.

Noriss, J. P.↗
NASA NTRS1993

Gravitational Waves and gamma-ray Bursts

If the gamma-ray burst sources detected by GRO are coalescing binaries at cosmological distances there should be a coincident gravitational radiation signal. Using the GRBs rate we predict the gravitational radiation detection rate as a function of the gravitational wave strain at Earth. This method of predicting the rate avoids the large statistical uncertainties in the current estimates that are based on the three neutron star binaries containing pulsars found, so far, in the Galaxy. The brightest gamma-ray bursts should be accompanied by a gravitational pulse detectable by LIGO or VIRGO, and by using the bursts as triggers for LIGO/VIRGO their sensitivity can be improved by 50% and the detection rate increases by a factor of 3. LIGO/VIRGO must reach a strain sensitivity of 10(sup-20.7)h(sub 0) to detect one burst per decade, and a failure to find coincidences at a rate of one per year with a strain sensitivity of 10(sup -20.6)h(sub 0) will rule out the binary hypothesis. If they are detected as gravitational wave sources, the time delay between the gamma-rays and the gravitational waves will help to determine the burst mechanism, and the polarization of the gravitational waves will help to determine the burst geometry.

Kochanek, Christopher S.↗
NASA NTRS1994

A Possible Cyclotron Line Signature from Quiescent Gamma-Ray Burst Counterparts

If gamma-ray bursts are associated with isolated, magnetized neutron stars in the Galaxy, they may be accreting directly from the interstellar medium after the burst event. In addition to a soft thermal component (T(sub e) approx. 100 eV), we predict that the faint quiescent emission spectra from these sources will possess a unique nonthermal signature: for magnetic field strengths B approx. equal to(0.7-7) x 10(exp 12) G, approx. 0.5-5% of the total luminosity could be emitted in a narrow (E/Delta E approx. 2-4) cyclotron emission line which peaks between approx. 5-20 keV below the cyclotron resonance energy (E(sub B) = 11.6(B/10(exp 12) G) keV). Unlike the soft thermal emission, this hard cyclotron component will not be strongly absorbed by the intervening H I gas. For stars with B approx. 10(exp 12) G, this nonthermal feature should be detectable by the instruments onboard ASCA and on the next generation of X-ray satellites (e.g., ASTRO-E). We therefore propose that deep X-ray images be taken on gamma-ray burst sources with excellent positions (error boxes less than or approx. equal to l') such as is being planned for GRB920501 to look for this feature. A positive detection would strongly suggest that at least some of the gamma-ray bursters are associated with isolated, magnetized neutron stars in the Galaxy.

Wang, John C. L.↗
NASA NTRS1984

3 keV to 2 MeV observations of four gamma-ray bursts

Simultaneous X and gamma ray spectra were obtained for four gamma ray burst events using satellite instrumentation. The P78-1 satellite proportional counters recorded X-ray data in the 3-10 keV range, while Pioneer Venus Orbiter and ISEE 3 sensors had a 3 keV lower limit for events. The positively correlated data covered the events GB 790307, 790325, 790504, and 790731. The time histories of the X and gamma ray energies did not correlate well. The post-gamma ray phase of GB 790307 displayed features of simple cooling, and in conjunction with soft X-ray data suggested an origin in an optically thin fireball. However, the data were equally well-fitted by a model of an emitting hot spot on a neutron star. The data negated any concept that gamma ray bursts evolve similarly to classical X-ray bursts.

Laros, J. G.↗
NASA NTRS1995

Observations of Gamma-Ray Bursts

Some basic observed properties of gamma-ray bursts are reviewed. Although some properties were known 25 years ago, new and more detailed observations have been made by the Compton Observatory in the past three years. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of weak bursts which would be expected from a homogeneous burst distribution. This is not compatible with any known Galactic population of objects. Gamma-ray bursts show an enormous variety of burst morphologies and a wide spread in burst durations. The spectra of gamma-ray bursts are characterized by rapid variations and peak power which is almost entirely in the gamma-ray energy range. Delayed gamma-ray burst photons extending to GeV energies have been detected for the first time. A time dilation effect has also been reported to be observed in gamma-ray, bursts. The observation of a gamma-ray burst counterpart in another wavelength region has yet to be made.

Fishman, G. J.↗
DOE OSTI2023

On the Anticorrelation between Duration and Redshift in Gamma-Ray Bursts

Abstract For gamma-ray bursts (GRBs) with durations greater than two seconds (so-called long GRBs), the intrinsic prompt gamma-ray emission appears, on average, to last longer for bursts at lower redshifts. We explore the nature of this duration–redshift anticorrelation, describing systems and conditions in which this cosmological evolution could arise. In particular, we explore its dependence on the metallicity of a massive star progenitor, because we can securely count on the average stellar metallicity to increase with decreasing redshift. Although stars with higher metallicity/lower redshift lose mass and angular momentum through line-driven winds, in some cases these stars are able to form more extended accretion disks when they collapse, potentially leading to longer-duration GRBs. We also examine how this duration–redshift trend may show up in interacting binary models composed of a massive star and compact object companion, recently suggested to be the progenitors of radio-bright GRBs. Under certain conditions, mass loss and equation-of-state effects from massive stars with higher metallicity and lower redshift can decrease the binary separation. This can then lead to spin-up of the massive star and allow for a longer-duration GRB upon the massive star’s collapse. Finally, the duration–redshift trend may also be supported by a relatively larger population of small-separation binaries born in situ at low redshift.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1994

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the 16 events is fitted by a power law of photon spectral index -2.0 +/- 0.4. The high-energy emission extends for at least 25 s. The most probable direction for this burst is determined from the directions of the 16 gamma rays observed by Egret and also by requiring the position to lie on annulus derived by the Interplanetary Network.

Sommer, M.↗
NASA NTRS2009

All-Sky Earth Occultation Observations with the Fermi Gamma-Ray Burst Monitor

Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux by determining the change in count rate due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. We will present early results. Regularly updated results can be found on our website http://gammaray.nsstc.nasa.gov/gbm/science/occultation.

Wilson-Hodge, C. A.↗
NASA NTRS2009

All-Sky Earth Occultation Observations with the Fermi Gamma-Ray Burst Monitor

Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/ soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. In addition, to Earth occultations, we have observed numerous occultations with Fermi's solar panels.

Wilson-Hodge, C. A.↗
NASA NTRS2010

All-Sky Earth Occultation Observations with the Fermi Gamma Ray Burst Monitor

Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique. Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors and spanning 150 keV to 40 MeV for the GBM BGO detectors. Our preliminary catalog consists of galactic X-ray binaries, the Crab Nebula, and active galactic nuclei. New sources are added to our catalog as they become active or upon request. In addition to Earth occultations, we have observed numerous occultations with Fermi's solar panels. We will present early results. Regularly updated results will be found on our website http://gammaray.nsstc.nasa.gov/gbm/science/occultation.

Wilson-Hodge, C. A.↗
NASA NTRS2014

Earth Occultation Monitoring with the Fermi Gamma Ray Burst Monitor

Using the Gamma Ray Burst Monitor (GBM) on-board Fermi, we are monitoring the hard X-ray/soft gamma ray sky using the Earth occultation technique (EOT). Each time a source in our catalog is occulted by (or exits occultation by) the Earth, we measure its flux using the change in count rates due to the occultation. Currently we are using CTIME data with 8 energy channels spanning 8 keV to 1 MeV for the GBM NaI detectors for daily monitoring. Light curves, updated daily, are available on our website http://heastro.phys.lsu.edu/gbm. Our software is also capable of performing the Earth occultation monitoring using up to 128 energy bands, or any combination of those bands, using our 128-channel, 4-s CSPEC data. The GBM BGO detectors, sensitive from about 200 keV to 40 keV, can also be used with this technique. In our standard application of the EOT, we use a catalog of sources to drive the measurements. To ensure that our catalog is complete, our team has developed an Earth occultation imaging method. In this talk, I will describe both techniques and the current data products available. I will highlight recent and important results from the GBM EOT, including the current status of our observations of hard X-ray variations in the Crab Nebula.

Wilson-Hodge, Colleen A.↗
NASA NTRS1983

Gamma Ray Bursts: a 1983 Overview

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect; energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all; burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective; finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T. L.↗
NASA NTRS1995

Statistical properties of the time histories of cosmic gamma-ray bursts detected by the BATSE experiment of the Compton gamma-ray observatory

The main scientific objectives of the project were: (1) Calculation of average time history for different subsets of BATSE gamma-ray bursts; (2) Comparison of averaged parameters and averaged time history for different Burst And Transient Source Experiments (BASTE) Gamma Ray Bursts (GRB's) sets; (3) Comparison of results obtained with BATSE data with those obtained with APEX experiment at PHOBOS mission; and (4) Use the results of (1)-(3) to compare current models of gamma-ray bursts sources.

Sagdeev, Roald↗
NASA NTRS2003

Strategies for Studying the Sources of Gamma Ray Bursts

The study of gamma ray bursts (GRBs) has rapidly evolved in recent years with the discovery of their cosmological nature and with BATSE, BeppoSAX, HETE and the IPN enabling a wide variety of associated . afterglow measurements. Multiwavelength observations ranging through the radio, optical, soft and hard x-ray, and gamma-ray regimes have exploded the field of GRB interpretation. Also, the Amanda, Milagro and LIGO experiments can search for related neutrino, cosmic-ray photon, and gravitational radiation events, even with the delayed alerts, such as from the IPN. The infrared region, where the optical emissions from sources at the extreme distances may be shifted, will become important but is undersubscribed. The soon-to-be launched Swift mission will greatly broaden the GRB discipline, and a strategy for associated ground-based measurements is outlined. The need for the improved global distribution of all instruments, in particular, robotic infrared detectors, is cited.

Cline, T. L.↗
NASA NTRS1991

Fuzzy correlations of gamma-ray bursts

The origin of gamma-ray bursts is not known, both in the sense of the nature of the source emitting the radiation and literally, the position of the burst on the sky. Lacking unambiguously identified counterparts in any wavelength band studied to date, statistical approaches are required to determine the burster distance scale. Angular correlation analysis is one of the most powerful tools in this regard. However, poor detector resolution gives large localization errors, effectively beam smearing the positions. The resulting fuzzy angular correlation function is investigated and the generic isotropization that smearing induces on any intrinsic clustering is discussed. In particular, the extent to which gamma-ray burst observations by the BATSE detector aboard the Gamma-Ray Observatory might recover an intrinsic source correlation is investigated.

Hartmann, Dieter H.↗
NASA NTRS1989

Cyclotron resonant scattering in the spectra of gamma-ray bursts

Data on the GB880205 gamma-ray bursts are presented that have implications for the nature of gamma-ray burst sources. It is shown that cyclotron resonant scattering and Raman scattering account well for the positions, strengths, and shapes of the relative strengths of the first and second harmonics and their narrow widths. These results imply the existence of a superstrong (B of about 2 x 10 to the 12th G) magnetic field in the vicinity of the X-ray emission region of GB880205. Such a superstrong magnetic field points to a strongly magnetic neutron star as the origin of gamma-ray bursts, and to the fact that the gamma-ray sources belong to the Galaxy.

Lamb, D. Q.↗
NASA NTRS1985

Soft-spectrum gamma-ray bursts

A typical gamma to ray burst (GRB), when observed over the approximately 30 keV to 1 MeV range, has a 1 to 10 s duration and a spectrum describable in terms of a several-hundred-keV exponential function. However, KONUS data indicate that some GRBs may belong to a separate class of short (approximately 0.1 s), soft (kT 50 keV) events. This result has been questioned because the KONUS experiments, with only 4 s spectral time resolution and a lack of information approximately 30 keV, are not particularly well suited for the detection and study of these bursts. The UC Berkely/Los Alamos Solar X-Ray Spectrometer/GRB experiment on the International Cometry Explorer (ICE), with nearly continuous coverage of approxiomately one-sixth of the sky down to 5 keV at 0.5 s resolution, is better designed for such a task. Using ICE data, it was confirmed that soft-spectrum events do indeed exist, apparently with properties that set them apart from the general GRB population. Results from the ICE experiment are presented.

Laros, J. G.↗
NASA NTRS1990

Galactic neutron stars and gamma-ray bursts

The association of the gamma-ray burst phenomenon with Galactic neutron stars is investigated statistically, and the distance to presently observable gamma-ray bursts is constrained. This is done by calculating the spatial distribution and kinematic properties of a sample of Population I neutron stars and comparing their properties to those of observed gamma-ray bursts. Both brightness distribution and angular distribution on the celestial sphere are employed. Current observations suggest negligible correlation on small angular scales, large-scale isotropy, and a radial distribution that is approximately uniform to the distances currently observed. It is concluded that the distribution of Population I neutron stars is consistent with current observations if gamma-ray bursts occur continuously throughout the neutron star lifetime and if the current sampling depth is at least about 150 pc but not more than roughly 2 kpc.

Hartmann, Dieter↗