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NASA NTRS1992

BATSE's sky sensitivity map

The Burst and Transient Source Experiment (BATSE) detects any gamma-ray burst not obscured by the earth and intense enough to produce a sufficiently strong signal in at least two of its eight large area NaI detectors (LADs). For a given intensity, a LAD records a stronger signal from a source which directly faces it than from a source to its side. Thus, BATSE's detection of a gamma-ray burst may depend upon the burst's direction. We discuss the effect of this uneven exposure to the sky on the instrument's measurement of the distribution of gamma-ray burst directions and intensities, and we describe our method of accounting for the effect.

Brock, M. N.↗
NASA NTRS1993

Data analysis tasks: BATSE

Miscellaneous tasks related to the operation of, and analysis of data from, the Burst and Transient Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) were performed. The results are summarized and relevant references are included.

Paciesas, William S.↗
NASA NTRS1993

Lunar scout missions: Galileo encounter results and application to scientific problems and exploration requirements

The Lunar Scout Missions (payload: x-ray fluorescence spectrometer, high-resolution stereocamera, neutron spectrometer, gamma-ray spectrometer, imaging spectrometer, gravity experiment) will provide a global data set for the chemistry, mineralogy, geology, topography, and gravity of the Moon. These data will in turn provide an important baseline for the further scientific exploration of the Moon by all-purpose landers and micro-rovers, and sample return missions from sites shown to be of primary interest from the global orbital data. These data would clearly provide the basis for intelligent selection of sites for the establishment of lunar base sites for long-term scientific and resource exploration and engineering studies. The two recent Galileo encounters with the Moon (December, 1990 and December, 1992) illustrate how modern technology can be applied to significant lunar problems. We emphasize the regional results of the Galileo SSI to show the promise of geologic unit definition and characterization as an example of what can be done with the global coverage to be obtained by the Lunar Scout Missions.

Head, J. W.↗
NASA NTRS1995

Search for Compton-backscattered annihilation radiation from the galactic center with the OSSE

An emission feature near 170 keV, interpreted as Compton-backscattered 511 keV positron-annihilation radiation, has been reported twice by balloon-borne germanium spectrometers from within approximately 15 deg of the Galactic center (Leventhal, MacCallum, & Stang 1978; Smith et al. 1993). Upper limits on this feature set by HEAO 3 (Mahoney, Ling, & Wheaton 1993) and other instruments indicate that it must be transient. We have searched data from the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (CGRO) for this feature, using daily spectral accumulations from all pointings near the Galactic center up to 1993 August, and covering most of the region viewed by the balloon instruments. We find no evidence for backscatter emission. Under the hypothesis that the source is 1E 1740.7-2942, the OSSE data set (186 days) disagrees with the balloon measurements with 99.3% confidence. The average daily 3 sigma OSSE upper limit on bakscatter flux from 1E 1740.7-2942 is 6.8 x 10(exp -4) photons/sq cm/s, compared to the 1.3 x 10(exp -3) photons/sq cm reported by the balloon observations. We also saw no evidence in 186 days for linelike emission from the point source EXS 1737.9-2952 recently discovered by Grindlay, Covault, & Manandhar (1993). This source exhibited bright emission from 83-111 keV, which has been interpreted as doubly backscattered 511 keV radiation. The average daily 3 sigma upper limit from OSSE for this line is 9.8 x 10(exp -4) photons/sq cm/s, or approximately 8% of the reported flux.

Smith, D. M.↗
NASA NTRS1995

RE J1255+266: Detection of an extremely bright EUV transient

During a pointed ROSAT observation in the direction of the Coma cluster of galaxies an exceptionally bright EUV source, RE J1255+266, was detected serendipitously. The source is located close to the Galactic North Pole, at b(sub II) is approximately or equal to 89 deg. Its observed EUV flux (62 - 110 eV) at the time of the detection was of order 7 x 10(exp -9) ergs/sq cm, making RE J1255+266 temporarily one of the brightest EUV sources on the sky. The EUV flare of RE J1255+266 has a light curve with a decay time of about 0.86 days. With respect to earlier non-detections, the source brightened by a factor of approximately 7000. Such a behavior has not been observed before. Thus, it is unclear what type of source RE J1255+266 might be. Up to now no positive identification with any known source could be obtained. Emission at the position of the source was previously only detected in the 1987 Green Bank radio continuum survey. Simultaneous observations with Compton Gamma Ray Observatory/Burst and Transient Source Experiment (CGRO/BATSE) resulted in non-detections of the source in the 8 - 50 keV energy range.

Dahlem, M.↗
NASA NTRS1997

Measuring the 511 keV emission in the direction of 1E1740.7-2942 with BATSE

Observations of the 511 keV emission in the direction of 1E 1740.7-2942 (1E) using the earth burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO), are presented. The CGRO phase 1 average spectrum of 1E is calculated using a method which assumes that a given source spectrum is the sum of the flux coming directly from the object and the contribution from the surrounding diffuse emission. The 1E light curve is calculated in the 40 to 150 keV range. It presents a constant flux excess of 70 mCrab in comparison with observations from the SIGMA gamma ray telescope onboard the GRANAT observatory. By removing this contribution, the 1E spectral transition from the low state to the high standard state observed by SIGMA is confirmed, and it is shown that the 511 keV flux is independent of the 1E long term evolution from low state to high standard state. It is concluded that the 511 keV emission of (4.2 +/- 1.3) x 140(exp -4) photons/sq cm s observed in the direction of 1E is mainly diffuse and spatially extended.

Wallyn, P.↗
NASA NTRS1997

The bursting pulsar GRO J1744-28

The source GRO J1744-28 was discovered on 2 December 1995 with the burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO) when a series of 80 untriggered, hard X-ray bursts were recorded. The direction of the observed bursts was consistant with the Galactic center. The source was observed to emit at a constant rate of between 20 and 30 bursts per day for a five month period finishing the 2 May 1996. In mid-December 1996, a persistent source appeared from the same general direction which was identified as a binary pulsar orbiting a low mass companion. Pulsations were discovered in the bursts, thus establishing a common identity for the source of the bursts and the pulsar. The BATSE observations in the temporal and spectral domains are reviewed. Results of the subsequent multiwavelength observations are described.

Kouveliotou, C.↗
NASA NTRS1997

BATSE as an all-sky monitor for INTEGRAL

It is proposed to use data from the burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO) as a sensitive, rapid, all sky monitor for the International Gamma Ray Astrophysics Laboratory (INTEGRAL). The all sky earth occultation monitoring and imaging capabilities of BATSE will complement and extend the Galactic plane scans of INTEGRAL as well as provide high latitude Galactic coverage which is inaccessible to INTEGRAL. Examples of transients previously observed by BATSE, its sensitivity, and the response time for these observations are described. Examples of the variability of several of the brighter sources observed by BATSE are shown.

Fishman, G. J.↗
NASA NTRS1997

BATSE imaging survey of the Galactic plane

The burst and transient source experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO) provides all sky monitoring capability, occultation analysis and occultation imaging which enables new and fainter sources to be searched for in relatively crowded fields. The occultation imaging technique is used in combination with an automated BATSE image scanner, allowing an analysis of large data sets of occultation images for detections of candidate sources and for the construction of source catalogs and data bases. This automated image scanner system is being tested on archival data in order to optimize the search and detection thresholds. The image search system, its calibration results and preliminary survey results on archival data are reported on. The aim of the survey is to identify a complete sample of black hole candidates in the galaxy and constrain the number of black hole systems and neutron star systems.

Grindlay, J. E.↗
NASA NTRS1997

Observations of Accreting Pulsars

We summarize 5 years of continuous monitoring of accretion-powered pulsars with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Our 20-70 keV observations have determined or refined the orbital parameters of 13 binaries, discovered five new transient accreting pulsars, measured the pulsed flux history during outbursts of 12 transients (GRO J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32, EXO 2030+375, GRO J1008-57, A0535+26, GRO J2058+42, 4U 1145-619, and A1118-616), and also measured the accretion torque history during outbursts of six of those transients whose orbital param- eters were also known. We have also continuously measured the pulsed flux and spin frequency for eiaht persistently accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U 1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity over a long baseline, BATSE observations have provided new insights into the long-term behavior of accreting magnetic neutron stars. We have found that all accreting pulsars show stochastic variations in their spin frequencies and luminosities, including those displaying secular spin-up or spin-down on long timescales, which blurs the con- ventional distinction between disk-fed and wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in outbursts of transient accreting pulsars but are uncorrelated, or even anti- correlated, in persistent sources. We describe daily folded pulse profiles, frequency, and flux measurements that are available through the Compton Observatory Science Support Center at NASA/Goddard Space Flight Center.

Bildsten, Lars↗
NASA NTRS1997

Observations of Accreting Pulsars

We summarize five years of continuous monitoring of accretion-powered pulsars with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Our 20-70 keV observations have determined or refined the orbital parameters of 13 binaries, discovered 5 new transient accreting pulsars, measured the pulsed flux history during outbursts of 12 transients (GRO J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32, EXO 2030+375, GRO J1008-57, A 0535+26, GRO J2058+42, 4U 1145-619 and A 1118-616), and also measured the accretion torque history of during outbursts of 6 of those transients whose orbital parameters were also known. We have also continuously measured the pulsed flux and spin frequency for eight persistently accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U 1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity over a long baseline, BATSE observations have provided new insights into the long-term behavior of accreting magnetic stars. We have found that all accreting pulsars show stochastic variations in their spin frequencies and luminosities, including those displaying secular spin-up or spin-down on long time scales, blurring the conventional distinction between disk-fed and wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in outbursts of transient accreting pulsars, but uncorrelated, or even anticorrelated, in persistent sources. We describe daily folded pulse profiles, frequency, and flux measurements that are available through the Compton Observatory Science Support Center at NASA-Goddard Space Flight Center.

Bildsten, Lars↗
NASA NTRS1999

The Earth Occultation Technique with the Burst and Transient Source Experiment

The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) is an uncollimated all-sky instrument sensitive to photons in the 20 keV to 1 MeV range. Since CGRO orbits the Earth at an altitude of 450 km, about 33% of the sky, as viewed with BATSE, is covered by the Earth at any given time. The entire sky is subject to Earth Occultation for some portion of CGRO's 52 day precession period. When a source sets below (or rises above) the Earth's limb, atmospheric attenuation produces step-like features in the BATSE data. The observed change in count rate in several energy bands provides a measurement of the source intensity and spectrum without sophisticated background models. These occultation features are used to locate and monitor astrophysical sources with BATSE when the source signal can be separated from the detector background. Examples of step searches, spectra light curves, and transform imaging are presented. Systematic uncertainties due to source confusion, detector response, and rapid background variations are discussed.

Wilson, C. A.↗
NASA NTRS2002

XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-ray Binary

XTE J1946+274 = GRO J1944+26 is a 15.8-s Be/X-ray pulsar discovered simultaneously in 1998 September with the, Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE). Pulse timing analysis yielded an orbital period of 169.2 days, a moderate eccentricity of 0.33, and implied a mass function of 9.7 solar mass. We observed evidence for an accretion disk, a correlation between measured spin-up rate and flux, which was fitted to obtain a distance estimate of 9.2 +/- 1.0 kpc. XTE J1946+274 remained active from 1998 September - 2001 July, undergoing 13 outbursts that were not locked in orbital phase. Comparing RXTE PCA observations from the initial bright outburst in 1998 and the last pair of outburst in 2001, we found energy and intensity dependent pulse profile variations in both outbursts and hardening spectra with increasing intensity during the fainter 2001 outbursts. In 2001 July, optical H(alpha) observations indicate a density perturbation appeared in the Be disk as the X-ray outbursts ceased. We propose that the equatorial plane of the Be star is inclined with respect to the orbital plane in this system and that this inclination may produce the unusual outburst behavior of the system.

Wilson, Colleen A.↗
NASA NTRS2002

Earth Occultation Techniques

Earth occultation is a familiar phenomenon to all residents of the Earth, although most know it as sunrise and sunset. Satellites observe Earth occultations of an astrophysical source when it sets behind or rises above the Earth's horizon (also called the Earth's limb). Two occultations, a rise and a set, occur every satellite orbit. The most extensive use of Earth occultation to measure sources was with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) for 9 years. The entire sky was subject to Earth occultation for some portion of CGRO's precession period. In BATSE data, atmospheric attenuation produced step-like features when astrophysical sources underwent occultation. The observed change in count rate in several energy bands provided a measurement of the source intensity and spectrum without requiring sophisticated background models. I will describe (1) a brief history of occultation techniques in X-ray and gamma ray astronomy; (2) how occultation features were used to locate and monitor astrophysical sources with BATSE and (3) how the Earth occultation technique can be applied to future instruments.

Wilson, Colleen A.↗
NASA NTRS2003

Analysis of Moessbauer Data from Mars: A Database and Artificial Neural Network for Identification of Iron-bearing Phases

The exploration of the planet Mars is one of the major goals within the Solar system exploration programs of the US-American space agency NASA and the European Space Agency ESA. In particular the search for water and life and understanding of the history of the surface and atmosphere will be the major tasks of the upcoming space missions to Mars. The miniaturized Moessbauer spectrometer MIMOS II has been selected for the NASA Mars-Exploration-Rover twin-mission to Mars in 2003 and the ESA 2003 Mars-Express Beagle 2 mission. Reduced in size and weight, in comparison to ordinary laboratory setup, the sensor head just weights approximately 400 g, with a volume of (50x50x90) cu mm, and holds two gamma-ray sources: the stronger for experiments and the weaker for calibrations. The collimator (in sample direction) also shields the primary radiation off the detectors. Around the drive four detectors are mounted. The detectors are made of Si-PIN-photodiodes in chip form (100 sq mm, thickness of 0.5 mm). The control unit is located in a separate electronics board. This board is responsible for the power supply, generation of the drive's velocity reference signal, read of the detector pulses to record the spectrum, data storage and communication with the host computer. After more than four decades from the discovery of the Moessbauer effect, more than 400 minerals were studied at different temperatures. Their Moessbauer parameters were reported in the literature, and have been recently collected in a data bank. Previous Mars-missions, namely Viking and Mars Pathfinder, revealed Si, Al, Fe, Mg, Ca, K, Ti, S and Cl to be the major constituents in soil and rock elemental composition of the red planet. More than 200 minerals already studied by Moessbauer spectroscopy contain significant amounts of these elements. A considerable number of Moessbauer studies were also carried out on meteorites and on Moon samples. Looking backward in the studies of the whole Moessbauer community, we have built a specific library containing Moessbauer parameters of those possible Mars minerals. The selected minerals, their Moessbauer parameter values (min. max. s.d and number of available data), main site substitution, behavior as a function of temperature and a ranking as expected to be found on Mars were organized. Mars-analogue Fe-bearing minerals not studied by Moessbauer spectroscopy are being collected and investigated. In addition, it an identification system based on Artificial Neural Networks (ANN) was implemented which enables fast and precise mineral identification from the experimental Moessbauer parameters at a given temperature.

P A de Souza Jr.↗
NASA NTRS2003

XTE J1946+274 = GRO J1944+26: An Enigmatic Be/X-Ray Binary

XTE J1946+274 = GRO J1944+26 is a 15.8 s Be/X-ray pulsar discovered simultaneously in 1998 September with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) and the All-Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer (RXTE). Here we present new results from BATSE and RXTE including a pulse timing analysis, spectral analysis, and evidence for an accretion disk. Our pulse timing analysis yielded an orbital period of 169.2 days, a moderate eccentricity 0.33, and implied a mass function of 9.7 solar masses. We observed evidence for an accretion disk, a correlation between measured spin-up rate and flux, which was fitted to obtain a distance estimate of 9.5 +/- 2.9 kpc. XTE J1946+274 remained active from 1998 September to 2001 July, undergoing 13 outbursts that were not locked in orbital phase. Comparing RXTE Proportional Counter Array observations from the initial bright outburst in 1998 and the last pair of outbursts in 2001, we found energy and intensity-dependent pulse profile variations in both outbursts and hardening spectra with increasing intensity during the fainter 2001 outbursts. In 2001 July, optical H alpha observations indicated that a density perturbation appeared in the Be disk as the X-ray outbursts ceased. We propose that the equatorial plane of the Be star is inclined with respect to the orbital plane in this system and that this inclination may be a factor in the unusual outburst behavior of the system.

Wilson, Colleen A.↗
DOE OSTI2026

Dark Photons from Perturbative Decay of a Misaligned Higgs Field

We reconsider the production of dark photons $A'$ as dark matter, from the perturbative decay of a dark Higgs field $h$, that is stochastically misaligned from the minimum of its potential during inflation. This is a simple and predictive framework for generating the $A'$ relic abundance. It is constrained by structure formation, since the $A'$ are initially boosted, and inflationary isocurvature fluctuations, which require small quartic couplings $λh^4$. We identify $A'$ masses between 100 eV and 1 GeV and gauge couplings $g\sim 10^{-15}-10^{-10}$ that are consistent in this scenario, and which become more tightly constrained if a generic level of kinetic mixing is present. The favored parameter region could be tested through future CMB or Lyman-$α$ observations, and, in the presence of kinetic mixing, by direct detection experiments or diffuse soft gamma-ray searches.

Cline, James M. [McGill U., Montreal (main)]↗
NASA NTRS1998

The Synchrotron Shock Model Confronts a "Line of Death" in the BATSE Gamma-Ray Burst Data

The synchrotron shock model (SSM) for gamma-ray burst emission makes a testable prediction: that the observed low-energy power-law photon number spectral index cannot exceed -2/3 (where the photon model is defined with a positive index: $dN/dE \propto E{alpha}$). We have collected time-resolved spectral fit parameters for over 100 bright bursts observed by the Burst And Transient Source Experiment on board the {\it Compton Gamma Ray Observatory}. Using this database, we find 23 bursts in which the spectral index limit of the SSM is violated, We discuss elements of the analysis methodology that affect the robustness of this result, as well as some of the escape hatches left for the SSM by theory.

Preece, Robert D.↗