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Kurfess, J. D.

Publications and source records attributed to Kurfess, J. D..

35 records · Page 2
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NASA NTRS1992

The Co-57 abundance in SN 1987A

Astrophysical implications of the detection by OSSE of Co-57 gamma radiation from SN 1987A are discussed. By burying the alpha-rich-freezeout portion at deeper gamma depths than in published models, it is shown that it remains barely possible that the bolometric luminosity during days 1200-1800 could derive from Co-57 power without requiring 57/56 production ratios greater than twice solar. Alternative mechanisms which may contribute to the bolometric power at late times are proposed.

Clayton, Donald D.↗
NASA NTRS1992

Operation and performance of the OSSE instrument

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Arthur Holly Compton Gamma Ray Observatory is described. An overview of the operation and control of the instrument is given, together with a discussion of typical observing strategies used with OSSE and basic data types produced by the instrument. Some performance measures for the instrument are presented that were obtained from pre-launch and in-flight data. These include observing statistics, continuum and line sensitivity, and detector effective area and gain stability.

Cameron, R. A.↗
NASA NTRS1992

OSSE spectral analysis techniques

Analysis of the spectra from the Oriented Scintillation Spectrometer Experiment (OSSE) is complicated because of the typically low signal to noise (approx. 0.1 percent) and the large background variability. The OSSE instrument was designed to address these difficulties by periodically offset-pointing the detectors from the source to perform background measurements. These background measurements are used to estimate the background during each of the source observations. The resulting background-subtracted spectra can then be accumulated and fitted for spectral lines and/or continua. Data selection based on various environmental parameters can be performed at various stages during the analysis procedure. In order to achieve the instrument's statistical sensitivity, however, it will be necessary for investigators to develop a detailed understanding of the instrument operation, data collection, and the background spectrum and its variability. A brief description of the major steps in the OSSE spectral analysis process is described, including a discussion of the OSSE background spectrum and examples of several observational strategies.

Purcell, W. R.↗
NASA NTRS1992

OSSE observations of the Crab pulsar

Preliminary results are presented of the Compton Gamma Ray Observatory Oriented Scintillation Spectrometer Experiment (OSSE) observations of the Crab pulsar. The pulsar energy spectra and light curves are in general agreement with previous observations, validating the OSSE pulsar data acquisition modes and data analysis algorithms. The data suggest that the spectrum of the pulsar varies throughout the light curve. The 'interpulse' region has a slightly flatter spectrum in the approx. 60 to 250 keV region and a slightly steeper spectrum at higher energies than the two main pulses. No evidence was found for any lines in the spectra with a typical sensitivity of about 10(exp -4) photons/sq cm/s.

Ulmer, M. P.↗
NASA NTRS1992

OSSE observations of galactic 511 keV annihilation radiation

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory has performed several observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron annihilation radiation. Preliminary analysis of data collected during the observation of the galactic center region over the period 13-24 Jun. 1991, indicates the presence of a 511 keV line and positronium continuum superimposed on a power-law continuum. The line of flux was found to be (2.7 +/- 0.5) x 10(exp -4) gamma/sq cm sec, with a positronium fraction of (0.9 +/- 0.2). The 3(sigma) upper limit to daily variations in the 511 keV line flux from the mean during the observation interval is 3 x 10(exp -4) gamma/sq cm sec. If all of the observed annihilation radiation is assumed to originate from the x-ray source 1E 1740.7-2942, the corresponding 511 keV line flux would be (3.0 +/- 0.6) x 10(exp -4) gamma/sq cm sec. The 3(sigma) upper limit for 511 keV line emission from the x-ray binary GX1+4 is 6 x 10(exp -4) gamma/sq cm sec. Results from the galactic plane observations at galactic longitudes of 25 degrees (16-21 Aug. 1991) and 339 degrees (6-11 Sep. 1991) suggest that the emission is concentrated near the galactic center. The observations and the preliminary results are described.

Purcell, W. R.↗
NASA NTRS1989

High energy flare physics group summary

The contributions of the High Energy Flare Physics Special Session in the American Astronomical Society Solar Physics Division Meeting are reviewed. Oral and poster papers were presented on observatories and instruments available for the upcoming solar maximum. Among these are the space-based Gamma Ray Observatory, the Solar Flare and Cosmic Burst Gamma Ray Experiment on the Ulysses spacecraft, the Soft X Ray Telescope on the spacecraft Solar-A, and the balloon-based Gamma Ray Imaging Device. Ground based observatories with new capabilities include the BIMA mm-wave interferometer (Univ. of California, Berkeley; Univ. of Illinois; Univ. of Maryland), Owens Valley Radio Observatory and the Very Large Array. The highlights of the various instrument performances are reported and potential data correlations and collaborations are suggested.

Ryan, J. M.↗
NASA NTRS1989

Capabilities of GRO/OSSE for observing solar flares

The launch of the Gamma Ray Observatory (GRO) near solar maximum makes solar flare studies early in the mission particularly advantageous. The Oriented Scintillation Spectrometer Experiment (OSSE) on GRO, covering the energy range 0.05 to 150 MeV, has some significant advantages over the previous generation of satellite-borne gamma-ray detectors for solar observations. The OSSE detectors will have about 10 times the effective area of the Gamma-Ray Spectrometer (GRS) on Solar Maximum Mission (SMM) for both photons and high-energy neutrons. The OSSE also has the added capability of distinguishing between high-energy neutrons and photons directly. The OSSE spectral accumulation time (approx. 4s) is four times faster than that of the SMM/GRS; much better time resolution is available in selected energy ranges. These characteristics will allow the investigation of particle acceleration in flares based on the evolution of the continuum and nuclear line components of flare spectra, nuclear emission in small flares, the anisotropy of continuum emission in small flares, and the relative intensities of different nuclear lines. The OSSE observational program will be devoted primarily to non-solar sources. Therefore, solar observations require planning and special configurations. The instrumental and operational characteristics of OSSE are discussed in the context of undertaking solar observations. The opportunities for guest investigators to participate in solar flare studies with OSSE is also presented.

Kurfess, J. D.↗
NASA NTRS1989

Long-term variations in the gamma-ray background on SMM

Long-term temporal variations in the various components of the background radiation detected by the gamma-ray spectrometer on the Solar Maximum Mission are presented. The SMM gamma-ray spectrometer was launched in February, 1980 and continues to operate normally. The extended period of mission operations has provided a large data base in which it is possible to investigate a variety of environmental and instrumental background effects. In particular, several effects associated with orbital precession are introduced and discussed.

Kurfess, J. D.↗
NASA NTRS1988

SMM detection of diffuse Galactic 511 keV annihilation radiation

Observations of the 511 keV annihilation line from the vicinity of the Galactic center from October to February for 1980/1981, 1981/1982, 1982/1983, 1984/1985, and 1985/1986 are presented. The measurements were made with the gamma-ray spectrometer on the SMM. The design of the instrument and some of its properties used in the analysis are described, and the methods used for accumulating, fitting, and analyzing the data are outlined. It is shown how the Galactic 511 keV line was separated from the intense and variable background observed in orbit. The SMM observations are compared with previous measurements of annihilation radiation from the Galactic center region, and the astrophysical implications are discussed. It is argued that most of the measurements made to date suggest the presence of an extended Galactic source of annihilation radiation.

Share, G. H.↗
NASA NTRS1985

Detection of galactic Al-26 gamma radiation by the SMM spectrometer

The Solar Maximum Mission satellite's gamma-ray spectrometer has detected a line near 1.81 MeV in each of the three years (1980-1982) over which the Galactic center traversed the broad aperture of that instrument. No significant intensity variation is noted over this period. The Galactic center/anticenter intensity ratio is greater than 2.5, and the center of the emission is noted to be consistent with the location of the Galactic center. For an assumed source distribution which follows the more than 100 MeV Galactic gamma radiation, the total flux in the direction of the Galactic center and the measured energy of the line are consistent with the detection of a narrow gamma-ray line from interstellar Al-26 by HEAO 3 in 1979-1980.

Share, G. H.↗
NASA NTRS1985

High-energy X-ray observations of the Galactic center region

The region within five degrees of the Galactic center was observed in high-energy X-rays on November 12, 1977, and it is concluded that the emission definitely comes from more than one source. At least five 2-10 keV sources are important: the transient A1743 - 322, the binary GX 1 + 4, the bulge sources GX 3 + 1 and GX 5 - 1, and A1742 - 294. The composite spectrum of all the sources agrees with the continuum measured 12 days earlier by Leventhal, MacCallum, and Stang (1978) in the 70-250 keV range but, if extrapolated to higher energies, would be softer than and weaker than the HEAO 1 continuum observed in September 1977 or HEAO 3 continuum observed in the fall of 1979.

Knight, F. K.↗
NASA NTRS1982

Balloon observations of galactic high-energy X-ray sources

A number of X-ray sources were observed with the Naval Research Laboratory hard X-ray observatory during balloon flights on 1976 May 11 and 1977 November 24. The primary objective of the observations was to characterize the temporal and spectral behavior of the sources in the energy range from 20 to 250 keV. Special emphasis was placed on the determination of spectrum versus phase for periodic sources and on the search for spectral features such as the reported 60 keV line in the X-ray spectrum of Her X-1. Results of the observations include: evidence for possible phase-dependent spectral variations in the emission from GX 1+4; flaring in the emission from GX 301-2; detection of unmodulated X-ray emission up to approximately 35 keV from GX 304-1; and an unexpectedly hard spectrum above 20 keV from Cyg X-2.

Maurer, G. S.↗
NASA NTRS1982

Observation of gamma-ray bursts from 10 keV to 9 MeV

Time histories and count-rate spectra of some of the gamma-ray bursts detected by the spectrometer on the Solar Maximum Mission between Feb. 20, 1980, and May 1981 are presented. Individual peaks observed in some of the bursts are found to differ significantly in hardness from one another. The similarity in the time profiles in the different energy bands is seen as suggesting that photons spanning two decades in energy are produced by the same mechanism. It is noted that all of the bursts are detected to energies greater than approximately 1 MeV. Two of the spectra presented are seen as being well fit by single power laws; the indices, however, are strikingly different. The other two sepctra require either two power laws or an exponential function. No clear evidence is found for the existence of narrow line features in any of the bursts.

Share, G. H.↗
NASA NTRS1980

The hard X-ray pulse profile of GX 1+4

Results are reported from 1976 and 1977 observations of the galactic center X-ray source GX 1+4. On these two occasions, epoch folding at twice the previously reported period of about two minutes has resulted in an asymmetry between the shapes of the two resultant peaks in the light curve, indicating that the true period may be about four minutes. Mean intensity is shown to vary from pulse to pulse.

Strickman, M. S.↗
NASA NTRS1978

Gamma ray spectroscopy in astrophysics: Future role of scintillation detectors

The future role of conventional scintillation detector telescopes for line gamma-ray astronomy is discussed. Although the energy resolution of the germanium detectors now being used by several groups is clearly desirable, the larger effective areas and higher efficiencies available with scintillation detectors is advantageous for many observations. This is particularly true for those observations of astrophysical phenomena where significant line broadening is expected.

Kurfess, J. D.↗
NASA NTRS1972

The impulsive X-ray burst of October 10, 1970.

An impulsive burst of 100-400 keV solar X-rays associated with a small solar flare was observed on October 10, 1970 with a large area scintillator aboard a balloon. The X-ray burst was also observed simultaneously in 10-80 keV range by the OGO-5 satellite and in 8-20 A range by the SOLRAD-9 satellite. The event is attributed to an H-alpha subflare located approximately at S13, E88 on the solar disk. The spectral characteristics of this event are examined in the light of the earlier X-ray observations of small solar flares.

Kane, S. R.↗