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NASA NTRS1983

Frequency of Fast, Narrow Gamma-ray Bursts and Burst Classification

Evidence from the Vela satellites that very brief, approximately 0.1 s, gamma-ray bursts constitute a class distinct from the longer, highly structured bursts has been strengthened by the results of the Venera 11 and 12 KKONUS experiments. The Goodard ISEE-3 gamma-ray burst spectrometer, utilizing a trigger criterion which is more likely to be independent of duration than previous experiments, detected a sample of events which enhances this bimodal distribution. The ISEE-3 result is corroborated by an increase in the frequency of detection of short bursts in the KONUS 13/14 database over KONUS 11/12, an effect attributable to the use of a shorter trigger integration time in the later experiments. Considerations such as repeating bursters complicate a simple dichotomous classification of gamma-ray bursts.

Norris, J. P.↗

NASA NTRS1994

Neutrino bursts from gamma-ray bursts

If gamma-ray bursts originate at cosmological distances, as strongly indicated by the results from Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO), then ultrarelativistic ejecta are the likely consequence of the highly super-Eddington luminosity of the sources. If the energy injection rate varies with time, then the Lorentz factor of the wind also varies, and the shells of ejected matter collide with each other. The collisions between baryons produce pions which decay into high-energy photons, electrons, electron positron pairs, and neutrino pairs. The bulk Lorentz factor of approximately 300 is required if our model is to be compatible with the observed millisecond variability. The strongest gamma-ray bursts are observed to deliver approximately 10(exp -4) ergs/sq cm in 100-200 keV photons. In our scenario more energy may be delivered in a neutrino burst. Typical neutrinos may be approximately 30 GeV if the protons have a Maxwellian energy distribution, and up to approximately TeV if the protons have a power-law distribution. Such neutrino bursts are close to the detection limit of the DUMAND II experiment.

Paczynski, Bohdan↗

NASA NTRS1999

The Effect of Magnetic Fields on Gamma-Ray Bursts Inferred from Multi-Wavelength Observations of the Bursts of 23 January 1999

Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic outflow of particles from a massive explosion (the nature at which is still unclear) interacts with material surrounding the site of the explosion. Observations of the evolving changes in emission at many wavelengths allow us to investigate the origin of the photons, and so potentially determine the nature of the explosion. Here we report the results of gamma-ray, optical, infrared, submillimeter, millimeter and radio observations of the burst ORB990123 and its afterglow. Our interpretation of the data indicates that the initial and afterglow emissions are associated with three distinct regions in the fireball. The peak flux of the afterglow, one day after the burst, has a lower frequency than observed for other bursts; this explains the short-lived radio emission. We suggest that the differences between bursts reflect variations in the magnetic-field strength in the afterglow-emitting regions.

Galama, T. J.↗

NASA NTRS1973

A comparison of the recently observed soft gamma-ray bursts with solar bursts and the stellar super-flare hypothesis

The possibility that soft gamma ray bursts are versions of X-ray bursts typically seen in solar flares and not products of supernovae events is investigated. Results show that the bursts have longer time scales that those predicted for supernovae events. It was suggested that the bursts result from the acceleration of electron bremsstrahlung to high energies in a stellar flare event.

Stecker, F. W.↗

NASA NTRS1979

A 3-s delay in an optical burst from X-ray burst source MXB1735-44

Analysis of the arrival times of X-ray and optical bursts from the X-ray burst source MXB1735-44 shows that the onset of one optical burst was delayed 2.8 sec with respect to the X-ray burst. Observations of the pulses are accurate to less than or equal to five ms. The delay in the optical pulse may be attributed to light travel time in the system and/or the time needed to reprocess X-rays into light.

Mcclintock, J. E.↗

NASA NTRS1985

Search for optical bursts from the gamma ray burst source GBS 0526-66

Attempts were made to detect optical bursts from the gamma-ray burst source GBS 0526-66 during Dec. 31, 1984 to Jan. 2, 1985 and Feb. 23 to Feb. 24, 1985, using the one meter reflector of the Kavalur Observatory. Jan. 1, 1985 coincided with the zero phase of the predicted 164 day period of burst activity from the source (Rothschild and Lingenfelter, 1984). A new optical burst photon counting system with adjustable trigger threshold was used in parallel with a high speed photometer for the observations. The best time resolution was 1 ms and maximum count rate capability was 255,000 counts s(-1). Details of the instrumentation and observational results are presented.

Seetha, S.↗

NASA NTRS1987

Multipeaked X-ray bursts from 4U/MXB 1636-53 - Evidence for burst-induced accretion disk coronae

The specific features of multipeaked X-ray bursts from 4U/MXB 1636-53, which are relatively weak and show no correlated photospheric radius expansion or contraction near the burst maximum, are explained using a model in which the observed luminosity is the sum of the direct component from the central source attenuated through an accretion disk corona and a component due to diffuse scattering by the corona. According to this model, the central peak in the triple-peaked burst results from an enhanced scattering emissivity of the direct component. At large inclination angles, the direct component may be unobservable; a burst detected via the scattered component only would be relatively short, weak, and would have similar rise and decay times. The direct and scattered components can be distinguished by X-ray polarimetry.

Melia, Fulvio↗

NASA NTRS1989

Non-Planckian behaviour of burst spectra - Dependence of the blackbody radius on the duration of bursts

Exosat observations indicate a strong correlation between X-ray burst duration and the blackbody temperature measured at the moment when the flux has decayed to 10 percent of the Eddington flux. No correlation is observed between the persistent flux near the burst and this temperature. Burst spectra reveal deviations from a Planckian spectrum which depend upon the chemical composition of the bursting layer. It is noted that this composition is not a simple function of the accretion rate.

Damen, E.↗

NASA NTRS1992

Gamma-ray burst locations from the Burst and Transient Source Experiment

The Burst and Transient Source Experiment (BATSE) consists of eight anisotropic gamma-ray spectrometers at the corners of the Compton Gamma Ray Observatory. BATSE monitors the full sky from a fixed orientation and determines the direction of gamma-ray bursts with an accuracy appropriate for studying the bursts' celestial distribution. We describe the calculation of gamma-ray burst directions from measurements made by BATSE. We present a sample of calculated directions from BATSE's measurement of solar flaxes and compare the calculated directions with the solar direction. We describe the systematic errors apparent in these data and discuss ongoing efforts to correct them.

Brock, M. N.↗

NASA NTRS1994

Burst-by-burst laser frequency monitor

The invention is a system for real-time frequency monitoring and display of an RF burst where the burst frequency is analyzed and displayed on a burst-by-burst basis in order to allow for frequency control. Although the invention was made for monitoring the laser frequency of a LIDAR system, it has other applications where realtime monitoring is required. The novelty of the invention resides in the use of a counter that is reset at the beginning of each unit time of monitoring and then gated for a unit of time. The invention also has an LED bar graph for displaying the measure of frequency at the end of each unit time in either a bar length mode or a moving dot mode. In the latter mode, the operator makes necessary adjustments to maintain the dot at the center of the bar graph.

Esproles, Carlos↗

NASA NTRS1999

The BATSE Gamma-Ray Burst Spectral Catalog: High Time Resolution Spectroscopy of Bright Bursts Using High Energy Resolution Data - 1

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 Abstract: Observatory, each covering a different aspect of burst phenomenology. In this paper, we present time-sequences of spectral fit parameters for 156 bursts selected either for their high peak flux or fluence.

Preece, Robert D.↗

NASA NTRS2004

Swift Gamma-Ray Burst Explorer: Mission Design for Rapid, Accurate Location of Gamma-ray Bursts

The Swift Gamma-ray Burst Explorer is a NASA Mid-sized Explorer (MIDEX) with the primary mission of determining the origins of Gamma-Ray Bursts (GRBs). It will be the first mission to autonomously respond to newly-discovered GRBs and provide immediate follow-up narrow field instruments capable of multi-wavelength (UV, Optical, X-ray) observations. The characteristics of GRBs that are the key mission design drivers, are their non-repeating and brief duration bursts of multi-wavelength photons. In addition, rapid notification of the location and characteristics of the GRBs to ground-and-space- based observatories drive the end-to-end data analysis and distribution requirements. The Swift mission is managed by the GSFC, and includes an international team of contributors that each bring their unique perspective that have proven invaluable to the mission. The spacecraft bus, provided by Spectrum Astro, Inc. was procured through a Rapid Spacecraft Development Office (RSDO) contract by the GSFC. There are three instruments: the Burst Alert Telescope (BAT) provided by the GSFC; the X-Ray Telescope (XRT) provided by a team led by the Pennsylvania State University (PSU); and the Ultra-Violet Optical Telescope (UVOT), again managed by PSU. The Mission Operations Center (MOC) was developed by and is located at PSU. Science archiving and data analysis centers are located at the GSFC, in the UK and in Italy.

Bundas, David J.↗

NASA NTRS2012

The Second SWIFT Burst Alert Telescope (BAT) Gamma-Ray Burst Catalog

We present the second Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts. (GRBs), which contains 476 bursts detected by the BAT between 2004 December 19 and 2009 December 21. This catalog (hereafter the BAT2 catalog) presents burst trigger time, location, 90% error radius, duration, fluence, peak flux, time-averaged spectral parameters and time-resolved spectral parameters measured by the BAT. In the correlation study of various observed parameters extracted from the BAT prompt emission data, we distinguish among long-duration GRBs (L-GRBs), short-duration GRBs (S-GRBs), and short-duration GRBs with extended emission (S-GRBs with E.E.) to investigate differences in the prompt emission properties. The fraction of L-GRBs, S-GRBs and S-GRBs with E.E. in the catalog are 89%, 8% and 2% respectively. We compare the BAT prompt emission properties with the BATSE, BeppoSAX and HETE-2 GRB samples.. We also correlate the observed prompt emission properties with the redshifts for the GRBs with known redshift. The BAT T(sub 90) and T(sub 50) durations peak at 70 s and 30 s, respectively. We confirm that the spectra of the BAT S-GRBs are generally harder than those of the L-GRBs.

Sakamoto, T.↗

NASA NTRS2013

Probing the Cosmic Gamma-Ray Burst Rate with Trigger Simulations of the Swift Burst Alert Telescope

The gamma-ray burst (GRB) rate is essential for revealing the connection between GRBs, supernovae and stellar evolution. Additionally, the GRB rate at high redshift provides a strong probe of star formation history in the early universe. While hundreds of GRBs are observed by Swift, it remains difficult to determine the intrinsic GRB rate due to the complex trigger algorithm of Swift. Current studies of the GRB rate usually approximate the Swift trigger algorithm by a single detection threshold. However, unlike the previously own GRB instruments, Swift has over 500 trigger criteria based on photon count rate and additional image threshold for localization. To investigate possible systematic biases and explore the intrinsic GRB properties, we develop a program that is capable of simulating all the rate trigger criteria and mimicking the image threshold. Our simulations show that adopting the complex trigger algorithm of Swift increases the detection rate of dim bursts. As a result, our simulations suggest bursts need to be dimmer than previously expected to avoid over-producing the number of detections and to match with Swift observations. Moreover, our results indicate that these dim bursts are more likely to be high redshift events than low-luminosity GRBs. This would imply an even higher cosmic GRB rate at large redshifts than previous expectations based on star-formation rate measurements, unless other factors, such as the luminosity evolution, are taken into account. The GRB rate from our best result gives a total number of 4568 +825 -1429 GRBs per year that are beamed toward us in the whole universe.

simulations↗

NASA NTRS1978

Discovery of optical bursts from an X-ray burst source, MXB1735-44

The optical counterpart of 4U 1735-44, X-ray burst source MXB 1735-44, was studied with the 1.5-m telescope at Cerro Tololo, and by SAS 3, during the period between June 1 and 3, 1978. Explanations for the optical activity are discussed in terms of accretion instabilities onto a neutron star, or thermonuclear flashes on the neutron star itself. Attention is given to the timing of the bursts, which indicate that the burst source probably is located in a region within 1-2 light seconds from the X-ray source. In the binary case, it is noted that the optical emission is probably removed from the X-ray heated stellar atmosphere of the possible companion.

Grindlay, J. E.↗

NASA NTRS1986

Comets, X-ray bursts, and gamma-ray bursts

The proposal, revived by Tremaine and Zytkow (1985), that accretion of comets by neutron stars may be the origin of gamma-ray bursts is considered. This mechanism has difficulty accounting for the observed gamma-ray spectrum and optical counterparts of the bursts. The survival of comets near supernovae is investigated. Ablation rates and the thermal structure of an ablating surface layer are calculated. In some circumstances, mechanical disruption will erode a comet more rapidly than evaporation. The accretion of comets by neutron stars may produce a class of X-ray burst sources with novel properties.

Katz, J. I.↗

NASA NTRS1987

Multipeaked X-ray bursts from 4U/MXB 1636-53 - Evidence against burst-induced accretion disk coronae

The burst-induced accretion-disk corona (BIADC) model proposed by Melia (1987) to explain the multiple-peak burst profiles of 4U/MXB 1636-53 in terms of direct and scattered components is examined critically. Published observational data (Sztajno et al., 1986, and Lewin et al., 1987) are presented in tables and graphs and analyzed. A number of possible BIADC scenarios are discussed, and it is argued that the observed characteristics of the 1636-53 bursts are not well accounted for by the BIADC model.

Penninx, W.↗

NASA NTRS1994

A study of gamma ray burst continuum properties presnting evidence for two spectral states in bursts

Evidence is presented for the existence of two spectral states contributing simultaneously to the total spectrum observed in many gamma-ray bursts (GRB's). An ensemble of 120 GRB's measured by BATSE were studied, using 4 channel spectral data, to determine in which bursts the spectral states can be most effectively resolved. The technique of summing the low intensity spectra together to get an average spectrum allows for precise characterization of the average low intensity spectral behavior. The 4 and 16 channel spectra obtained by the BATSE Large Area Detectors (LAD's) are analyzed using a model-independent spectral inversion technique. The results of these analyses applied to an individual burst are discussed in detail.

Pendleton, Geoffrey N.↗