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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Constraints on galactic distributions of gamma-ray burst sources from BATSE observations

The paradigm that gamma-ray bursts originate from Galactic sources is studied in detail using the angular and intensity distributions observed by the Burst and Transient Source Experiment (BATSE) on NASA's Compton Gamma Ray Observatory (CGRO). Monte Carlo models of gamma-ray burst spatial distributions and luminosity functions are used to simulate bursts, which are then folded through mathematical models of BATSE selection effects. The observed and computed angular intensity distributions are analyzed using modifications of standard statistical homogeneity and isotropy studies. Analysis of the BATSE angular and intensity distributions greatly constrains the origins and luminosities of burst sources. In particular, it appears that no single population of sources confined to a Galactic disk, halo, or localized spiral arm satisfactorily explains BATSE observations and that effects of the burst luminosity function are secondary when considering such models. One family of models that still satisfies BATSE observations comprises sources located in an extended spherical Galactic corona. Coronal models are limited to small ranges of burst luminosity and core radius, and the allowed parameter space for such models shrinks with each new burst BATSE observes. Multiple-population models of bursts are found to work only if (1) the primary population accounts for the general isotropy and inhomogeneity seen in the BATSE observations and (2) secondary populations either have characteristics similar to the primary population or contain numbers that are small relative to the primary population.

Hakkila, Jon↗
NASA NTRS1992

Structure in gamma ray burst time profiles: Statistical Analysis 1

Since its launch on April 5, 1991, the Burst And Transient Source Experiment (BATSE) has observed and recorded over 500 gamma-ray bursts (GRB). The analysis of the time profiles of these bursts has proven to be difficult. Attempts to find periodicities through Fourier analysis have been fruitless except one celebrated case. Our goal is to be able to qualify the observed time-profiles structure. Before applying this formation to bursts, we have tested it on profiles composed of random Poissonian noise. This paper is a report of those preliminary results.

Lestrade, John Patrick↗
NASA NTRS1992

Search for evidence of low energy protons in solar flares

We searched for linear polarization in the H alpha line using the Stokes Polarimeter at Mees Solar Observatory and present observations of a flare from NOAA active region 6659 which began at 01:30 UT on 14 Jun. 1991. Our dataset also includes H alpha spectra from the Mees charge coupled device (MCCD) imaging spectrograph as well as hard x ray observations from the Burst and Transient Source Experiment (BATSE) instrument on board the Gamma Ray Observatory (GRO). The polarimeter scanned a 40 x 40 inch field of view using 16 raster points in a 4 x 4 grid. Each scan took about 30 seconds with 2 seconds at each raster point. The polarimeter stopped 8.5 inches between raster points and each point covered a 6 inch region. This sparse sampling increased the total field of view without reducing the temporal cadence. At each raster point, an H alpha spectrum with 20 mA spectral sampling is obtained covering 2.6 A centered on H alpha line center. The preliminary conclusions from the research are presented.

Metcalf, Thomas R.↗
NASA NTRS1994

Miocrowave spectral imaging, H-alpha and hard X-ray observations of a solar limb flare

We compare the microwave, H-alpha, and hard X-ray observations for a west limb C7.3 flare that occurred at 17:10 UT, 1992 June 26. H-alpha movies were obtained at Big Bear Solar Observatory. Before the onset of the flare, overexposed H-alpha images show the complicated flux loop structure above the limb. Material was observed to descend along the loops toward the site where the flare occurred hours later. Using the five-antenna solar array at Owens Valley Radio Observatory, we obtain two-dimensional maps of flare emission from 1.4 to 14 GHz. In all three temporal peaks of the microwave bursts, the maps show the same characteristics. The peak low-frequency emission comes from the top of one bundle of the H-alpha loops and gradually shifts to the foot-point of the loops (the location of H-alpha flare) as the frequency increases. The location of the emission peak shifts 88 sec between 1 and 14 GHz. Seventy percent of the shift occurs between 1 and 5 GHz. The locus of the shift of the emission peak follows the shape of an H-alpha surge that occurred after the flare. For each point along the locus, we create the microwave brightness temperature spectrum and compare the radio-derived electron distribution with that derived from the high-resolution hard X-ray spectra measured with Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO). We find that the peak frequency changes from approximately 3 GHz at the loop top to approximately 7 GHz at the footprint, presumably due to the increase of the magnetic field from approximately 160 GHz at the loop top to approximately 300 G at the footpoint. The high-frequency slope of the microwave power-law spectrum decreases from approximately 10 at the loop top to approximately 5 at the footprint due to a change in the energy distribution of the dominant electrons. The microwave brightness temperature spectral index predicted by the BATSE power-law hard X-ray spectra agrees with the measured value only at the footpoint. At the loop top, the emission may be thermal gyrosynchrotron with a temperature of 3.5 x 10(exp 7) K, which is likely to correspond to the superhot component seen in the hard X-ray emission.

Wang, H.↗
DOE OSTI2023

Creating a high energy alert system for the HAWC gamma ray observatory

One of the greatest mysteries in astrophysics is exactly how Cosmic Rays (CRs) are accelerated up to extremely high energies within our galaxy. The highest-energy galactic CRs are associated with gamma rays at ~100 TeV. Hadronic models of possible CR accelerators, including supernova remnants and pulsars, require the production of both gamma rays and neutrinos at these sources. Searching for coincidences between neutrino and the highest energy gamma ray observations can help confirm these theories. The High Altitude Water Cherenkov (HAWC) observatory is a ground based gamma ray observatory located in Puebla, Mexico. HAWC is able to detect gamma rays with energies greater than 100 TeV. It has a wide field of view and a 95% duty cycle, making it ideal for these types of coincidence searches. This work aims to create a high energy alert system for HAWC, sending out an alert to other experiments for high-energy gamma ray events it sees.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

OSSE observations of GX 339-4

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) observed the Galactic black hole candidate GX 339-4 as a target of oppurtunity in 1991 September, in response to the outburst reported by Burst and Transient Source Experiment (BATSE). We report here on energy spectra in the 50 keV-10 MeV range obtained by OSSE. The source was detected from 50 to 400 keV at a level relative to the Crab Nebula of approximately 30%. The observed spectrum was prescribed reasonably well by a power law with an exponential cutoff; a least-squares fit yielded a photon index of 0.88 +/- 0.05 and a cutoff energy of 68 +/- 2 keV. The addition of a Compton reflection component did not significantly improve the overall fit. An optically thin thermal bremsstrahlung spectrum also provides a good fit, and the thermal Comptonization model of Sunyaev & Titarchuk, while deficient in describing the data above approximately 200 keV, cannot formally be ruled out. A pure power law with reflection does not fit the observed spectrum. During a follow-up observation made in 1991 November the intensity of the source below 100 keV had dropped by more than a factor of 40, and it was no longer detected above approximately 100 keV. The energy spectrum during the November observation could be characterized by a power law with a photon index of 2.3 +/- 0.3; the spectrum was fitted equally well with the same exponentially cutoff power-law model applied to the September observation, reduced in intensity by a factor of approximately 40. During the 1991 September observation, the luminosity in the 50-400 keV band was approximately 2 x 10(exp 37) ergs/s (assuming a distance of 4 kpc), no more than a factor of 5 below the soft X-ray luminosity of GX 339-4 observed in its X-ray high state. The luminosity during the 1991 November observation was approximately 5 x 10(exp 35) ergs/s. Extrapolations of both the exponentially cutoff power-law and Sunyaev-Titarchuk models to the approximately 5-20 keV X-ray band yield flux levels very close to that observed by Ginga during an overlapping interval in 1991 September, when GX 339-4 was reported to be in its low state. This may be one of the strongest indications to date of a direct correspondence between the low X-ray state and gamma-ray outbursts of GX 339-4.

Grabelsky, D. A.↗
NASA NTRS1999

Long-Term Hard X-Ray Monitoring of X-Ray Bursters

The scientific goal of this project was to monitor a selected sample of x-ray bursters using data from the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory to characterize the hard x-ray emission of these objects over long time intervals. The project was closely related to "Monitoring x-ray emission from x-ray bursters", NASA project, and "Hard x-ray emission of x-ray bursters", NASA project, and shares publications in common with both of these. These efforts have lead to results directly from the BATSE data and also from Target of Opportunity Observations (TOO) made with the Rossi X-Ray Timing Explorer based on detection of transient hard x-ray outbursts with BATSE. The following papers have used BATSE data or data obtained with BATSE TOO triggers.

Halpern, Jules P.↗
NASA NTRS1997

Discovery of the 198 s X-Ray Pulsar GRO J2058+42

GRO J2058+42, a transient 198 second x-ray pulsar, was discovered by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO), during a "giant" outburst in 1995 September-October. The total flux peaked at about 300 mCrab (20-50 keV) as measured by Earth occultation. The pulse period decreased from 198 s to 196 s during the 46-day outburst. The pulse shape evolved over the course of the outburst and exhibited energy dependent variations. BATSE observed five additional weak outbursts from GRO J2058+427 each with two week duration and peak pulsed flux of about 15 mcrab (20-50 keV), that were spaced by about 110 days. An observation of the 1996 November outburst by the Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) localized the source to within a 4' radius error circle (90% confidence) centered on R.A. = 20 h 59 m.0, Decl. = 41 deg 43 min (J2000). Additional shorter outbursts with peak pulsed fluxes of about 8 mCrab were detected by BATSE halfway between the first four 15 mCrab outbursts. The RXTE All-Sky Monitor detected 8 weak outbursts with approximately equal durations and intensities. GRO J2058+42 is most likely a Be/X-ray binary that appears to outburst at periastron and apastron. No optical counterpart has been identified to date and no x-ray source was present in the error circle in archival ROSAT observations.

Wilson, Colleen A.↗
NASA NTRS1971

Observation of Pulsed Gamma Rays with Energies Greater than 250 keV from the Crab Nebula Pulsar NP 0532

Data from a balloon flight experiment using an Na I scintillation spectrometer were analyzed for gamma ray pulsation. The payload was carried to a nominal atmospheric depth of 3.5 g/cm2. A superposed epoch analysis was performed on a 12,000 second portion of the data spanning a total time interval of 16,700 seconds at float altitude. A positive pulsed contribution was observed at the expected apparent frequency of NP 0532 having the typical double pulse structure. The results indicate a time-averaged pulse photon flux of 0.00144 + or - 0.00057 photons/sq cm/sec in the energy interval from 250 keV to 2.3 MeV. This represents a time-averaged pulsed power of 0.000649 + or - 0.000257 keV/sq cm/sec/keV. The ratio of interpulse to main pulse was found to be 2.4 + or - 1.9. The analysis indicates a positive photon flux from 250 keV to 725 keV of 0.00120 + or - 0.00052 photons/sq cm/sec.

Orwig, L. E.↗
NASA NTRS1994

Observation of GX 339-4 hard state outbursts in 1991 and 1992

Two hard state (X-ray low state) outbursts in the GX 339-4 system in 1991 June-October and 1992 September-1993 January were detected and monitored by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO). The outbursts were remarkably similar in both temporal and spectral aspects. The spectrum in the 20-300 keV band evolves from a hard, Comptonized shape to a steeper (alpha approximately equals -3) power law during each outburst.

Harmon, B. A.↗
NASA NTRS1995

The effects of pure density evolution on the brightness distribution of cosmological gamma-ray bursts

In this work, we explore the effects of burst rate density evolution on the observed brightness distribution of cosmological gamma-ray bursts. Although the brightness distribution of gamma-ray bursts observed by the BATSE experiment has been shown to be consistent with a nonevolving source population observed to redshifts of order unity, evolution of some form is likely to be present in the gamma-ray bursts. Additionally, nonevolving models place significant constraints on the range of observed burst luminosities, which are relaxed if evolution of the burst population is present. In this paper, three analytic forms of density evolution are examined. In general, forms of evolution with densities that increase monotonically with redshift require that the BATSE data correspond to bursts at larger redshifts, or to incorporate a wider range of burst luminosities, or both. Independent estimates of the maximum observed redshift in the BATSE data and/or the range of luminosity from which a large fraction of the observed bursts are drawn therefore allow for constraints to be placed on the amount of evolution that may be present in the burst population. Specifically, if recent measurements obtained from analysis of the BATSE duration distribution of the actual limiting redshift in the BATSE data at z(sub lim) = 2 are correct, the BATSE N(P) distribution in a Lambda = 0 universe is inconsistent at a level of approximately 3 alpha with nonevolving gamma-ray bursts and some form of evolution in the population is required. The sense of this required source evolution is to provide a higher density, larger luminosities, or both with increasing redshift.

Horack, J. M.↗
NASA NTRS2002

Low-Energy Study of Gamma-Ray Bursts Using Two BATSE Spectroscopy Detectors

Gamma-ray bursts (GRBs) are energetic, short-duration emissions of gamma-rays from astronomical sources typically well beyond our galaxy. The Burst and Transient Source Experiment (BATSE) that was onboard NASA's Compton Gamma-Ray Observatory (CGRO) had detected an unprecedented 2704 GRBs during CGRO's nine-year mission. BATSE consisted of eight detector assemblies located at the corners of CGRO to give full sky coverage. Each assembly consisted of two detectors, a Large Area Detector (LAD) and a Spectroscopy Detector (SD). In determining the detail features of GRBs, the degree to which they possess a low-energy component (approx. 10 keV) is of interest. Preece have developed a method to study the low-energy characteristics and concluded that 14% of the 86 bright GRBs they studied had a definite low-energy component, referred to as a low-energy excess. Their study, and for the present study as well, needed to use SD data, because it extends down to the low-energy range when operating in a high-gain mode. For their study, low-energy data was used from just one SD. To better quantify the low-energy behavior, this study will consider bursts for which two SDs satisfy the same criteria as used by Preece.

Michael J. Pangia↗
NASA NTRS1985

Low-energy and medium-energy gamma rays from PSR 0531 + 21

Results are presented from the Crab Pulsar PSR 0531 + 21 for energies of 0.3-30 MeV. For energies of 1-30 MeV, the absolute phase and separation of the first and second pulses 12.9 + or - 0.3 ms, widths of the pulses 2.2 + or - 0.5 ms FWHM, and 1.6 + or - 0.4 ms FWHM, ratio of the counts in the second to the first pulse 0.64 + or - 0.33 and ratio of counts in the interpulse region to the total pulsed counts 0.17 + or - 0.30 are compared to te results vor energies, E greater than 50 MeV and their variations with time. Values from the phase plots for E greater than 0.3 MeV are compared with low-energy gamma rays during 1970 through 1980 from several experiments with energies from about 20 to 360 keV. The above suggest different production mechanisms for low- and high-energy gamma rays with a transition at about 1 MeV. Derived fluxes from 0.3 to 30 MeV confirm a previously derived power law.

White, R. S.↗
NASA NTRS2007

Performance of the Three-Dimensional Track Imager (3-DTI) for Gamma-Ray Telescopes

We have been developing a gas time projection chamber for the imaging of gamma-rays between 0.3 - 50 MeV, the Three-Dimensional Track Imager (3DTI). The detector is being designed for use on satellite experiments for the imaging of astrophysical gamma-ray sources. Electrons produced by pair production or Compton scattering ionize the gas and these ionization electrons are detected by the cross-strip micro-well detector at the bottom of the chamber. Discrete component of front end electronics and time digitization electronics have been developed. We will present results of prototype microwell detector and laboratory set-up in various gas mixtures.

Son, Seunghee↗
NASA NTRS1994

BATSE gamma-ray burst line search. 2: Bayesian consistency methodology

We describe a Bayesian methodology to evaluate the consistency between the reported Ginga and Burst and Transient Source Experiment (BATSE) detections of absorption features in gamma-ray burst spectra. Currently no features have been detected by BATSE, but this methodology will still be applicable if and when such features are discovered. The Bayesian methodology permits the comparison of hypotheses regarding the two detectors' observations and makes explicit the subjective aspects of our analysis (e.g., the quantification of our confidence in detector performance). We also present non-Bayesian consistency statistics. Based on preliminary calculations of line detectability, we find that both the Bayesian and non-Bayesian techniques show that the BATSE and Ginga observations are consistent given our understanding of these detectors.

Band, D. L.↗
DOE OSTI2023

The High-Altitude Water Cherenkov (HAWC) observatory in México: The primary detector

The High-Altitude Water Cherenkov (HAWC) observatory is a second-generation continuously operated, wide field-of-view, TeV gamma-ray observatory. The HAWC observatory and its analysis techniques build on experience of the Milagro experiment in using ground-based water Cherenkov detectors for gamma-ray astronomy. HAWC is located on the Sierra Negra volcano in México at an elevation of 4100 meters above sea level. The completed HAWC observatory principal detector (HAWC) consists of 300 closely spaced water Cherenkov detectors, each equipped with four photomultiplier tubes to provide timing and charge information to reconstruct the extensive air shower energy and arrival direction. The HAWC observatory has been optimized to observe transient and steady emission from sources of gamma rays within an energy range from several hundred GeV to several hundred TeV. However, most of the air showers detected are initiated by cosmic rays, allowing studies of cosmic rays also to be performed. This paper describes the characteristics of the HAWC main array and its hardware.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

New Experiments for Detecting Emissions from Fission

Ensuring that nuclear science and technology is used solely for peaceful purposes is one of the most pressing challenges facing our society. The Consortium for Monitoring, Technology, and Verification (MTV) mission is to help meet this challenge by providing advanced technology and trained talent for careers in nuclear security and nonproliferation. The study of nuclear fission is one area of interest in the MTV. We are performing new experiments for the characterization of neutron and gamma ray emissions from fission fragments. These emissions are signatures for the detection and characterization of nuclear materials. To perform these experiments, we have developed Fission Sphere (FS-3), an array of forty organic stilbene detectors operated in time-coincidence. The FS-3 is used to measure the prompt emissions of neutrons and gamma rays from Cf-252 spontaneous fission. These new data will be used to validate physics-based prediction codes, including CGMF and FREYA, and will be useful in future ENDF and ENSDF evaluations. This paper will present results from the first experiments using FS-3 and a Cf-252 spontaneous fission source. It will compare the experimental results with predictions from theory and Monte Carlo simulation. Specifically, we will describe the correlations among energy, multiplicity, and angles of emitted particles. We will also discuss the application of these correlations in multiplicity counting techniques, which are widely used in nuclear safeguards.

Pozzi, S. A.↗
NASA NTRS1999

Monitoring X-Ray Emission from X-Ray Bursters

The scientific goal of this project was to monitor a selected sample of x-ray bursters using data from the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer together with data from the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory to study the long-term temporal evolution of these sources in the x-ray and hard x-ray bands. The project was closely related to "Long-Term Hard X-Ray Monitoring of X-Ray Bursters", NASA project NAG5-3891, and and "Hard x-ray emission of x-ray bursters", NASA project NAG5-4633, and shares publications in common with both of these. The project involved preparation of software for use in monitoring and then the actual monitoring itself. These efforts have lead to results directly from the ASM data and also from Target of Opportunity Observations (TOO) made with the Rossi X-Ray Timing Explorer based on detection of transient hard x-ray outbursts with the ASM and BATSE.

Halpern, Jules P.↗