Solar flares with photon emission above 10 MeV - Measurements with the gamma ray experiment on board the SMM-satellite
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Rieger, E.↗
Engineering topics
Forrest, D. J.
Publications and source records attributed to Forrest, D. J..
Nuclear gamma rays and interplanetary proton events
From February 1980 - February 1982, the Gamma Ray Spectrometer on the Solar Maximum Mission satellite observed the impulsive phases of sixteen western hemisphere flares that were associated with prompt solar proton events. Six of these flares had a detectable excess in the 4-8 MeV window and four others had detectable continuum emission above 300 keV. As indicated in earlier studies based on fewer events, a lack of correlation is found between the peak 10 MeV near-earth proton fluxes and prompt gamma-ray-line fluences. The two largest proton events in the sample did not have detectable emission above 300 keV. For the 9 December event, an upper limit for the density of the ion acceleration region of 8 billion/cu cm or less is obtained for an acceleration time constant of 1500 s.
Cliver, E. W.↗
Solar gamma-ray lines
The gamma-ray spectrometer on the Solar Maximum Mission satellite has observed emissions produced by nuclear reactions in over 20 separate solar flares. The observed intensity from different flares ranges over a factor of 100, and the time scale for their production ranges from 10-s pulses to complete events lasting over 1000 s. The emissions include narrow and broadened prompt gamma-ray lines from numerous isotopes from Li-7 to Fe-56 and cover the energy range from 0.431 MeV (Be-7) to 7.12 MeV (O-16). The instrument has also observed emissions at energies greater than 10 MeV from the decay of pi0 mesons, from electron bremsstrahlung, and from the direct observation of greater-than-100-MeV solar neutrons. The intensity, temporal and spectral properties of these emissions are reviewed from the point of view that solar flares represent an astrophysical particle-acceleration site.
Forrest, D. J.↗
Positron annihilation radiation from solar flares
Positron-annihilation radiation has been observed from the June 21, 1980 and June 3, 1982 flares by the gamma-ray spectrometer on the Solar Maximum Mission satellite. The observed 0.511-MeV line fluences from the flares were 14.6 + or - 3.3 gamma/sq cm and 103 + or - 8 gamma/sq cm, respectively. Measurement of the line width establishes an upper limit to the temperature in the annihilation region of 3 x 10 to the 6th K. The time dependence of the 0.511-MeV line during the 1980 flare is consistent with the calculations of Ramaty et al. (1983) for positrons created in the decay of radioactive nuclei. The time dependence of the 0.511-MeV line for the 1982 flare is more complex and requires more detailed study.
Share, G. H.↗
Upper limits of narrow annihilation lines in gamma-ray bursts
The SMM gamma-ray experiment has observed 60 gamma-ray bursts from March 1980 to August 1982. Details of one burst are illustrated. There is weak evidence for a broadened spectral feature early in the burst, which was also detected by the Konus experiment. The present detailed search is limitd to narrow lines (less than 70 keV FWHM) near 500 keV; none is found in any of the bursts. This absence contrasts with the reported detection of several broader features (Mazets et al., 1981). The implications for the physical conditions in the annihilation region are discussed.
Nolan, P. L.↗
Effects of line width and spatial extent on measurements of the 0.51 MeV Galactic center line
Over the past 15 years, a number of measurements have been made of positron-electron annihilation radiation from the Galactic Center region. The results after 1979 show a significant decrease in measured flux intensity from that previously observed with the same instruments. This is probably due to time variations; however, the contributions of a spatially extended and/or energy-broadened component should also be considered. The entire data set is consistent with a time variable point source plus a distribution along the Galactic Disk. There is no strong evidence for a component broadened in energy.
Dunphy, P. P.↗
A direct observation of solar neutrons following the 0118 UT flare on 1980 June 21
The Gamma Ray Spectrometer on the Solar Maximum Mission satellite has observed energetic solar neutrons (greater than 50 MeV) at the earth following a solar flare that occurred on the west limb on June 21, 1980 at 01:18:20 UT. Impulsive photon emission from 10 keV to greater than 65 MeV lasting over a period of about 66 s was followed by a transient flux of 50-600 MeV neutrons incident over a 17 minute period. The peak counting rate corresponds to an average flux at the earth of (3.8 + or - 0.6) x 10 to the -2nd neutrons/sq cm s at 130 MeV. These observations indicate the emission of 3 x 10 to the 28th neutrons/sr with energies greater than 50 MeV, requiring the rapid acceleration (much less than 60 s) of protons to GeV energies during the impulsive phase of the flare.
Chupp, E. L.↗
A coded aperture gamma ray telescope
A gamma ray telescope is being developed to operate in the energy range 100 keV to 5 MeV, utilizing coded aperture imaging. The design incorporates a mask pattern based on a Uniformly Redundant Array (URA), which has been shown to have ideal imaging characteristics. A mask-anti-mask procedure is used to eliminate the effects of any possible systematic variations in detector background rates. The detector array is composed of 35 elements of the high-Z material Bismuth Germanate (BGO). Results of laboratory testing of the imaging properties will be presented. A southern hemisphere balloon flight is planned for 1982 with the goal of observing the 0.511 MeV radiation from the Galactic Center. Computer calculations show that a point source of this radiation can be located to within + or - 1 deg.
Mcconnell, M. L.↗
Upper limits to pulsed gamma ray emission from PSR 0833-45, 1747-46, and 1818-04
Pulsed gamma ray emission from three pulsars (PSR 0833-45, 1747-46, and 1818-04) have been sought on a balloon flight of the University of New Hampshire Large Gamma Ray Telescope, which incorporates a shielded sodium iodide scintillator array, and was launched from Alice Springs, Australia. Over the energy range 0.1 - 10 MeV, no evidence is found for pulsed gamma rays, and upper limits are set for Vela which are comparable to, or below, the extrapolation to lower energies of the pulsed emission reported by SAS-2 and COS-B.
Cherry, M. L.↗
Observation of gamma-ray bursts with the SMM gamma-ray spectrometer
The gamma-ray spectrometer on SMM is sensitive to bursts within its field of view with intensities greater than 0.000005 erg/sq cm above 100 keV. It has detected 17 events between February 1980 and March 1981 with the characteristics of cosmic gamma-ray bursts. The most intense burst, on 19 April 1980, had a photon spectrum consistent with a power law with spectral index - 2.5 from 300 keV to approximately 7 MeV. It is not possible at present to exclude the sun as the source of this burst. Spectra of 11 of the bursts have been studied for line features with no clear evidence for line emission greater than 300 keV. The continuum radiation from about half of these events have hard emission extending to approximately equal to or greater than 2 MeV.
Share, G. H.↗
Evidence for impulsive ion acceleration during the 0312 UT flare of 1980 June 7
One of the basic problems concerning the physics of solar flares is related to the process which is responsible for the acceleration of both electrons and ions. It has been proposed that the acceleration process proceeds in two different phases. The first phase results in the acceleration of electrons to energies in the range from 10 to 100 KeV. Electrons and ions with energies exceeding 30 MeV are finally produced during the second phase. Attention is given to the observational evidence which shows that these two phases, if in fact they are separate, must operate within seconds of each other, and that this process must be able to repeat itself producing pulses of electrons and ions approximately every 10 seconds. The observations were made with the Gamma Ray Spectrometer (GRS) on the SMM satellite during the 0312 UT flare on June 7, 1980.
Forrest, D. J.↗
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.↗
Spatial variation for flares observed with the gamma ray spectrometer aboard the SMM satellite
A search is made for anisotropic X-ray bremsstrahlung photon production from relativistic electrons by studying the heliocentric angular dependence of 53 flares detected at energies above 300 keV. No evidence is found for a higher rate of detectable flares near the limb at the 80 percent confidence level. This result implies that the X-ray directivity as defined by the ratio of photon intensity at 75 deg and 0 deg of heliocentric angle is less than 1.5 above 300 keV and strongly rejects any flare model predicting X-ray production from a radial 'beam' of energetic electrons.
Zolcinski, M. C.↗
Limit on galactic 6.13 MeV gamma-ray line
The University of New Hampshire large gamma-ray detector observed the galactic center region during a balloon flight from Alice Springs, Australia on 1977 November 21-22. The absence of any observable line at 6.13 MeV or its escape-peak energy makes it possible to place an upper limit of 8.1 x 10 to the -4th photons/(sq cm s) at the 99% confidence level on the 0-16 de-excitation line at this energy from the galactic disk in the direction of the center. This limit restricts the interpretation given by Willett et al. (1979) of the line at 6.13 MeV which they observed while viewing the galactic anticenter. The present results indicate that it is highly unlikely that the line which these authors report is due to dark nebulae or the quiet sun. Possible explanations for their observation are atmospheric background, local production in the detector, a localized cosmic source in the direction of the galactic anticenter, or a statistical fluctuation.
Dunphy, P. P.↗
Observation of the 2.223 MeV gamma-ray line on the SMM satellite - The event of 1980 June 7
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Chupp, E. L.↗
Observations with the SMM gamma-ray spectrometer - The impulsive solar flares of 1980 March 29
Gamma-ray continuum emission from 0.3 to 1 MeV was observed with the gamma-ray spectrometer on the Solar Maximum Mission satellite during two impulsive solar flares on 1980 March 29, from active region 2363 at 0918 UT and from active region 2357 at 0955 UT. Evidence is presented for a hardening of the spectrum during the impulsive phase of the flares. The photon intensity greater than 100 keV appears to decay at a slower rate than that at lower energies. Time-integrated photon spectra for both flares are incompatible with a single-temperature thermal-bremsstrahlung model. Upper limits for prompt and delayed gamma-ray lines are presented.
Ryan, J. M.↗
Statistical evaluation of gamma-ray line observations
The statistical reliability of reported positive observations of solar and cosmic gamma-ray lines has been evaluated. The relative probability that each measurement is due to a real source rather than to an accidental fluctuation in the background has been determined, and it is found that the results are statistically compelling in only a small fraction of the reported observations. At present, extreme caution must be exercised in drawing astrophysical conclusions from reports of the detection of cosmic gamma-ray lines.
Cherry, M. L.↗
The gamma ray spectrometer for the Solar Maximum Mission
The paper describes an actively shielded, multicrystal scintillation spectrometer for measurement of the solar gamma ray flux used by the Solar Maximum Mission Gamma Ray Experiment. The instrument provides a 476-channel pulse height spectrum every 16.38 s over the 0.3-9 MeV energy range; the gamma ray spectral analysis can be extended to at least 15 MeV on command. The instrument is designed to measure the intensity, energy, and Doppler shift of narrow gamma ray lines, the intensity of extremely broadened lines, and the photon continuum.
Forrest, D. J.↗