Engineering topics

Forrest, D. J.

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

At least 37 records · Page 2

NASA NTRS1985

Search for gamma ray lines from SS433

Data obtained with the Gamma Ray Spectrometer (0.3 to 9 MeV) aboard the Solar Maximum Mission satellite from 1980 to 1985 for evidence of the reported Doppler shifted lines from SS433 were examined. The data base covers a total of 468 days when SS433 was in the field of view and includes times of quiescent and flaring radio activity. In 9 day integrations of the SMM data no evidence is found for gamma ray line emission from SS433. The 99% confidence upper limits for 9 day integrations of the shifted 1.37 and 6.1 MeV lines are 0.0013 gamma/sq cm-s and 0.0007 gamma/sq cm-s, respectively. The 360 day time averaged upper limits are 0.0002 gamma/sq cm-s x 0.0001 gamma/sq cm-s for both lines.

Geldzahler, B. J.↗

NASA NTRS1985

SMM detection of interstellar Al-26 gamma radiation

The gamma ray spectrometer on the Solar Maximum Mission Satellite has detected the interstellar Al-26 line when the Galactic center traversed its aperture. The center of the emission is consistent with the location of the Galactic center, but the spatial distribution is presently not well defined. The total flux in the direction of the Galactic center is 4.3 + or - 0.4) x .0001 gamma/sq cm-s-rad for an assumed population I distribution.

Share, G. H.↗

NASA NTRS1985

Time extended production of neutrons during a solar flare

The most energetic neutral emissions expected from solar flares are gamma rays (10 MeV) from relativistic primary and secondary electron bremsstrahlung,from approx 0 meson decay, and from neutrons ( 50 MeV). Bremsstrahlung photon energies extend to that of the highest energy electron present, but the shape of the pi sup 0 gamma ray spectrum, peaking at 69 MeV, does not depend strongly on the proton spectrum above threshold, which is approx. 292 MeV for meson production on protons. The highest energy neutrons observed indicate directly the highest energy ions which interact at the Sun, and the presence or absence of anergy cutoff in the acceleration process. The high-energy proton spectrum shape can be determined from the neutron spectrum.

Chupp, E. L.↗

NASA NTRS1985

Neutral pion production in solar flares

The Gamma-Ray Spectrometer (GRS) on SMM has detected more than 130 flares with emission approx 300 keV. More than 10 of these flares were detected at photon energies 10 MeV. Although the majority of the emission at 10 MeV must be from electron bremsstrahlung, at least two of the flares have spectral properties 40 MeV that require gamma rays from the decay of neutral pions. It is found that pion production can occur early in the impulsive phase as defined by hard X-rays near 100 keV. It is also found in one of these flares that a significant portion of this high-energy emission is produced well after the impulsive phase. This extended production phase, most clearly observed at high energies, may be a signature of the acceleration process which produces solar energetic particles (SEP's) in space.

Forrest, D. J.↗

NASA NTRS1985

Abundances from solar-flare gamma-ray line spectroscopy

Elemental abundances of the ambient gas at the site of gamma ray line production inthe solar atmosphere are deduced using gamma ray line observations from a solar flare. The resultant abundances are different from local galactic abundances which are thought to be similar to photospheric abundances.

Murphy, R. J.↗

NASA NTRS1985

Solar flare gamma-ray line spectroscopy

The techniques and the results of solar elemental abundance determinations using observations of gamma ray lines from the April 27 1981 olar flare were outlined. The techniques are elaborated on and observed and the best-fitting theoretical spectra are presented. Numerical values for the photon fluences and the total number of protons involved in the thick-target production of these gamma rays are derived.

Murphy, R. J.↗

NASA NTRS1985

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays from an early design study employing Monte Carlo calculations. The response to 50 to 600 MeV solar neutrons was estimated from a simple model which did not consider secondary charged particles escaping into the veto shields. In view of numerous detections by the GRS of solar flares emitting high energy gamma rays, including at least two emitting directly detectable neutrons, the calibration of the high energy mode in the flight model has been recalculated by the use of more sophisticated Monte Carlo computer codes. New results presented show that the GRS response to gamma rays above 20 MeV and to neutrons above 100 MeV is significantly lower than the earlier estimates.

Cooper, J. F.↗

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

Photofraction of a 5 cm x 2 cm BGO scintillator

The photofraction of a 5.1 cm x 2.0 cm bismuth germanate (BGO) scintillator was measured over a gamma-ray energy range of 0.2 to 6.1 MeV. Several methods, used to minimize the effect of room scattering on the measurement, are discussed. These include a gamma-gamma coincidence technique, a beta-gamma coincidence technique, and the use of sources calibrated with a standard 7.6 cm x 7.6 cm sodium iodide scintillator.

Dunphy, P. P.↗

NASA NTRS1985

High-energy emission in gamma-ray bursts

Between February 1980 and August 1983 the Gamma-Ray Spectrometer on the Solar Maximum Mission Satellite (SMM) detected 72 events identified as being of cosmic origin. These events are an essentially unbiased subset of all gamma-ray bursts. The measured spectra of these events show that high energy (greater than 1 MeV) emission is a common and energetically important feature. There is no evidence for a general high-energy cut-off or a distribution of cut-offs below about 6 MeV. These observations imply a limit on the preferential beaming of high energy emission. This constraint, combined with the assumption of isotropic low energy emission, implies that the typical magnetic field strength at burst radiation sites is less than 1 x 10 to the 12th gauss.

Matz, S. M.↗

NASA NTRS1984

A 154-day periodicity in the occurrence of hard solar flares?

An analysis of the temporal distribution of 139 solar flares monitored by the Gamma Ray Spectrometer aboard the Solar Maximum Mission is reported. It is found that, instead of being randomly distributed in time, these events have a tendency to occur in groups with a mean spacing of about 154 days (75 nHz) over the observing interval. A larger sample of flares with an X-ray classification of M 2.5 or larger recorded by the GOES satellite showed a similar regularity.

Rieger, E.↗

NASA NTRS1984

Spectral feature of 31 December 1981 gamma-ray burst not confirmed

Measurements of a gamma ray burst at 01:37 UT on December 31, 1981 using the SMM gamma ray spectrometer (GRS) are compared with those made by the Konus instruments on Veneras 11-14. Burst time profiles, photon spectra, and detector energy loss spectra for three time intervals are compared for the GRS and the Konus instruments. It is concluded that the SMM spectra exhibit no evidence for the presence of emission features reported by the Konus group.

Nolan, P. L.↗

NASA NTRS1984

Electron-rich particle events and the production of gamma-rays by solar flares

The abundance of electrons of 5-50 MeV energies relative to protons of similar energy has been determined in a total of 49 particle events of apparently solar origin during the year 1980. Most events with high electron abundances appear to have been produced by flares which also produced observable fluxes of gamma-rays. The overall distribution of abundances is consistent with that measured in 1968-1970 at similar energies, but is systematically lower in electron content than abundance distributions measured at lower energies. Electron-rich particle events have harder electron spectra than more normal events, and are never accompanied by strong interplanetary shocks. Therefore, an investigation is conducted to decide whether observations are consistent with models in which energetic particles are accelerated by a shock produced at the flare site. It is concluded that, in such models, the variable nature of the interplanetary particle events must reflect some fundamental but variable property of the shocks - possibly their direction of propagation. An outward moving shock may produce a particle event in interplanetary space whereas a shock directed toward the sun may produce a flux of particles in the lower solar atmosphere which generate the gamma-radiation.

Evenson, P.↗

NASA NTRS1983

Simultaneous acceleration of electrons and ions in solar flares

Data from the observations of two gamma ray and electron bremsstrahlung X-ray emitting solar flares, on June 7 and 21, 1980, were used to examine the relative starting times of the energetic ion and electron interactions. The data were gathered by the SMM, which was viewing the 2.223 MeV line from H-1(n, gamma)H-2, the 0.511 MeV line from electron-positron annihilation, the prompt nuclear lines at 4.44 and 6.13 MeV from excited C-12 and excited O-16, and the energetic solar neutrons at 1 AMU. Excess gamma ray and X-ray emissions were detected at relatively the same times during both flares in all energy bands, and were attributed to ion-induced emissions. The timing of the peaks of electron and ion activity indicate that both electrons and ions are accelerated to their peak activity in under 5 sec.

Forrest, D. J.↗

NASA NTRS1983

Gamma-ray observational constraints on the origin of the optical continuum emission from the white-light flare of 1980 July 1

Results are presented for the flare of July 1, 1980, which started at approximately 1627 UT and in which simultaneous measurements were made of X-ray, gamma-ray, and optical continuum emission for the entire duration of the flare. The X-ray and gamma-ray observations were made by the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite. The optical measurements were taken at the Sacramento Peak Observatory and the Big Bear Solar Observatory (Zirin and Neidig, 1981). It is found that the major white-light emission that occurs in the late phase of the flare could not have been due to heating by electron or ion precipitation. This conclusion derives from the fact that the X-ray and gamma-ray flux peaks approximately 1 minute before the maximum of the optical continuum mission emission. It is also found that approximately 73 percent of the optical continuum emission, representing a spatially and temporally distinct bright point, follows this maximum with little or no X-ray or gamma-ray emission in the same period.

Ryan, J. M.↗

NASA NTRS1983

A directional gamma-ray telescope using coded aperture techniques

A directional detector for gamma-ray astronomy has been developed to image sources in the energy range 0.1 to 5 MeV. An array of 35 gain stabilized bismuth germanate detectors, together with a coded aperture mask based on a uniformly redundant array allows imaging in 4 deg square sky bins over a 16 x 24 deg field-of-view. The position of a strong point source, such as the Crab Nebula, can be determined to within not more than about 1 deg. A complementary 'anti-mask' greatly reduces systematic effects arising from nonuniform background rates amongst the detectors. The telescope has an effective area of 190 sq cm and an energy resolution of 19.5 percent FWHM at 662 keV. Results of laboratory tests of the imaging system, including the ability to image multiple sources, uniformity of response over the field-of-view, and the effect of the 'anti-mask', are in good agreement with computer simulations. Features of the flight detector system are described and results of laboratory tests and computer simulations are reviewed. A balloon flight of the telescope is planned for the fall of 1982.

Mcconnell, M. L.↗

NASA NTRS1983

The solar cosmic ray neutron event on June 3, 1982

The observation of solar neutrons from the earth has been reported. The observations were carried out June 3, 1982, following the intense gamma-ray line flare at 1143 UT. The emission spectra of the neutrons was calculated over an energy range from 40 MeV to 1.2 GeV, on the basis of measurements from a gamma-ray/neutron scintillation spectrometer, and the IGY Jungfraujoch neutron monitor at an altitude of 3500 m. Some possible terrestrial effects of the solar neutrons are discussed. It is shown that the calculated spectra conform to the requirement of ion acceleration to GeV energies a few seconds after the start of the impulsive phase of a solar ion flare event.

Debrunner, H.↗

NASA NTRS1983

Solar neutrons from the impulsive flare on 1982 June 3 at 1143 UT

A transient flux of high energy solar neutrons from 50 MeV to about 1 GeV has been detected by the Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission (SMM) satellite following an intense burst of high energy photons (less than 100 MeV) peaking at 1143:29 UT. The neutrons were also detected by the IGY neutron monitor on Jungfraujoch (Switzerland). In this paper the SMM GRS observations are summarized and compared with the Jungfraujoch neutron monitor data, and both the time dependent neutron flux at the earth and the neutron emission spectrum at the sun are estimated.

Chupp, E. L.↗