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

Abstract

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 3.4d_0.3 between 360-700 keV and by an exponential law of the form exp (--E/Eo) with E0=l.0• 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 n~ ~> 5 • 101~ cm -a in the production region, the number of electrons above 100 keV required to explain the results is ~< 2 x 10 a4.

ON THE SPECTRAL HARDENING AT ≳300 keV IN SOLAR FLARES

“…Later, Yoshimori et al (1985), using the Hinotori spacecraft, examined the hard X-ray (HXR) spectrum in a broad energy range (20 keV-7 MeV) for four flares that showed significant hardening at energies above ∼400 keV. They confirmed the earlier suggestion of Suri et al (1975) that the hardening in the continuum reflects an underlying hardening in the source electron spectrum. Spectral hardening also occurs in events where there are clear signatures of gamma-ray lines.…”

“…In 1975, Suri et al (1975) examined the X-ray and gamma-ray flux in the 1972 August 4 event and concluded that the X-ray and gammaray flux was produced by a single population of electrons with a break in its spectrum, instead of two separate populations acting independently. Later, Yoshimori et al (1985), using the Hinotori spacecraft, examined the hard X-ray (HXR) spectrum in a broad energy range (20 keV-7 MeV) for four flares that showed significant hardening at energies above ∼400 keV.…”

The Acceleration and Propagation of Solar Flare Energetic Particles

“…Shea andSmart 1973, Duggal 1979) and its interactions at the Sun are manifest in gamma-ray lines (Chupp et al 1973, Ramaty, Kozlovsky and Lingenfelter• 1975. Relativistic electrons are observed directly in interplanetary space (Simnett 1971, Datlowe 1971, Evenson, Meyer and Yanagita 1981 and their interactions at the Sun produce gamma-ray continuum (Suri et al 1975) and Type IV radio emission (e.g. Ramaty et al 1980).…”

Gamma-ray and microwave evidence for two phases of acceleration in solar flares

“…Gamma-ray emission in the energy interval from 0.35 to 8 MeV, containing both lines and continuum, has been observed during the 3B flare of 1972, August 4 (Chupp et aL , 1973Suri et al, 1975).…”

“…The implications of the line emissions have been investigated most recently by Ramaty, Kozlovsky, and Lingenfelter (1975), and interpretations of the continuum have been given by these authors, by Suri et al (1975), and by Bai and Ramaty (1975). The most likely mechanism for the production of continuum emission in the above energy region is bremsstrahlung of accelerated electrons.…”