D. J. Forrest

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.

The gamma ray spectrometer for the Solar Maximum Mission

The Solar Maximum Mission Gamma Ray Experiment (SMM GRE) utilizes an actively shielded, multicrystal scintillation spectrometer to measure the flux of solar gamma rays. The instrument provides a 476-channel pulse height spectrum (with energy resolution of ∼7% at 662 keV) every 16.38 s over the energy range 0.3–9 MeV. Higher time resolution (2 s) is available in three windows between 3.5 and 6.5 MeV to study prompt gamma ray line emission at 4.4 and 6.1 MeV. Gamma ray spectral analysis can be extended to ≳15 MeV on command. Photons in the energy band from 300–350 keV are recorded with a time resolution of 64 ms. A high energy configuration also gives the spectrum of photons in the energy range from 10–100 MeV and the flux of neutrons ≳20 MeV. Both have a time resolution of 2 s. Auxiliary X-ray detectors will provide spectra with 1-sec time resolution over the energy range of 10–140 keV. The instrument is designed to measure the intensity, energy, and Doppler shift of narrow gamma ray lines as well as the intensity of extremely broadened lines and the photon continuum. The main objective is to use this time and spectral information from both nuclear gamma ray lines and the photon continuum in a direct study of the dynamics of the solar flare/particle acceleration phenomena.

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

The gamma-ray spectrometer on the Solar Maximum Mission Satellite has detected a line near 1.81 MeV with a significance of >5 sigma in each of 3 yr when the Galactic center traversed the broad aperture of the instrument in 1980, 1981, and 1982. There was no significant variation in intensity from year to year. The Galactic center/anticenter intensity ratio is >2.5, and the center of the emission is consistent with the location of the Galactic center. The distribution could not be measured well enough to distinguish between candidate sources, e.g., novae, supernovae, red giants, and massive stars. For an assumed source distribution which follows the >100 MeV Galactic gamma radiation, the total flux measured in the direction of the Galactic center is (4.0 +- 0.4) x 10/sup -4/ ..gamma..(cm/sup 2/ s rad)/sup -1/. The measured energy of the line is 1.804 +- 0.004 MeV. These measurements are consistent with the detection of a narrow ..gamma..-ray line from interstellar /sup 26/Al by HEAO 3 in 1979/1980.

The Solar Maximum Mission Atlas of Gamma-Ray Flares

We present a compilation of data for all 258 gamma-ray —ares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray —are sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot cycle. We describe the SMM/GRS instrument, its in-orbit operation, and the principal data reduction methods used to derive the gamma-ray —are properties. Utilizing measurements for 185 —ares that were sufficiently intense to allow the derivation of gamma-ray spectra, we present an atlas of time pro—les and gamma-ray spectra. The —are parameters derived from the gamma-ray spectra include bremsstrahlung —uence and best-—t power-law parameters, narrow nuclear line —uence, positron annihilation line —uence, neutron capture line —uence, and an indi- cation of whether or not emissions greater than 10 MeV were present. Since a uniform methodology was adopted for deriving the parameters, this atlas should be very useful for future statistical and correlative studies of solar —ares. Subject headings: catalogsgamma rays: burstsSun: —ares

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.

Very energetic gamma-rays from the 3 June 1982 solar flare

Abstract The Gamma-Ray Spectrometer on the Solar Maximum Mission satellite has recorded high energy gamma-ray and neutron emission from the flare on 3 June 1982. During the 65 sec. impulsive phase the gamma rays > 10 MeV contains emissions from both primary electron bremsstrahlung and nuclear pion decay. Hence the impulsive phase acceleration process must produce both primary electrons with energies > 60 MeV and ions >500 MeV. This flare also has a extended emission phase lasting more than 1000 sec which is most easily observed at gamma-ray energies > 10 MeV. After removing the counting rates from the more slowly moving neutrons produced at earlier times, the resulting gamma ray spectrum can be entirely explained by nuclear pion production. We find that >70 % of the pions were produced in the extended emission phase. In contrast, more than 70 % of the high energy primary electron bremsstrahlung and the

A balloon-borne coded aperture telescope for low-energy gamma-ray astronomy

Abstract A telescope for imaging cosmic γ-ray emission over the energy range 160 keV to 9.3 MeV has been developed and successfully flown on a high altitude balloon over Palestine, Texas on 1 October, 1984. This instrument consists of a coded mask based on a 5 × 7 uniformly redundant array (URA) and a scintillator array consisting of 35 bismuth germanate (BGO) detectors. The telescope can image sources with an intrinsic resolution of 3.8° within a 15.2° × 22.8° field of view. The properties of the instrument are described and its imaging capability is demonstrated with results from an observation of the region of the Crab Nebula. The imaging response to the Crab was found to be well represented by a bivariate Gaussian function of full width at half-maximum (FWHM) 4.8°. The centroid of the response was determined to a precision of ± 12 arc min.

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 ±1°.

Observation of the 2.223 MeV gamma-ray line on the SMM satellite - The event of 1980 June 7

The Gamma-Ray Spectrometer on the Solar Maximum Mission satellite observed ..gamma..-ray lines during the 0312 UT solar flare on 1980 June 7. The impulsive X- and ..gamma..-ray event lasted for or approx. =50 MeV, produced during a approx.40 s interval overlapping the impulsive photon emission time interval. A total production of 4 x 10/sup 29/ neutrons is required, if they were produced isotropically.

Observations of solar gamma ray continuum between 360 keV and 7 MeV on August 4, 1972

Measurements were made of the time-averaged gamma ray energy loss spectrum in the energy range 360 keV to 7 MeV by the gamma ray detector on the OSO-7 satellite during the 3B flare on August 4, 1972. The differential photon spectrum unfolded from this spectrum after subtracting the background spectrum and contributions from gamma ray lines is best described by a power law with spectral index of 3.4±0.3 between 360–700 keV and by an exponential law of the form exp (-E/E0) with E0 = 1.0±0.1 MeV above 700 keV. It is suggested that this spectrum is due to nonthermal electron bremsstrahlung from a population of electrons, with a strong break in the spectrum at 2 MeV. Since the observational data indicates that the matter number density must be nH ⩾ 5 × 1010 cm-3 in the production region, the number of electrons above 100 keV required to explain the results is ⩽2 × 1034.