Guenter Rudolf Riegler

Variable positron annihilation radiation from the galactic center region

The HEAO 3 Cosmic Gamma-Ray Spectrometer performed the first high spectral resolution survey of the entire sky at gamma-ray energies from 50 keV to 10 MeV. Studies of 511 keV positron annihilation radiation from the vicinity of the galactic center are reported here, based on data which were recorded during 1979 September/October and 1980 March/ April. The 1979 fall data show unshifted, narrow 511 keV line emission of intensity (1.85 ± 0.21) X 10^(-3) photons cm^(-2) s^(-1), consistent with earlier measurements. The 1980 spring measurement showed a statistically significant reduction in 511 keV emission from this region, thus requiring that a significant fraction of the flux originate in one or more compact sources of size ≾ 10^(18) cm. While distribution of sources within ~ 22° (at 90% confidence level) of the direction of the galactic center are allowed by the observations, the data rule out most extended models for positron production, such as by cosmic ray interaction in the interstellar medium or by distributions of many supernovae, novae, or pulsars. The data are well satisfied by assuming that the emission originates in a single compact source at the galactic center.

A High Resolution Measurement of the 2.223 MeV Neutron Capture Line in a Solar Flare

An intense solar flare lasting 40 s was observed by the HEAO 3 γ-ray spectrometer on 1979 November 9 at 3:05 UT. The flare was observed in four high-resolution germanium detectors as well as in five CsI shield detectors over an energy range of 100 keV to above 5 MeV. Of particular interest is a line feature at 2.2248 ± 0.0010 MeV. The precise energy measurement provides unambiguous evidence that this is the ^1H(n,γ)^2H line resulting from neutron capture on hydrogen. An upper limit of 5 keV is found for the natural line width. The time dependence of the neutron capture line is discussed as well as the overall characteristics of the November 9 flare.

The gamma-ray spectrum of the galactic center region

The Galactic center region was observed with the HEAO 3 High Resolution Gamma-Ray Spectrometer during the fall of 1979 and the spring of 1980. Between these epochs there was observed (1) a statistically significant decrease in the high-energy (511 keV to about 3 MeV) luminosity, (2) a decrease in the positron annihilation line intensity, reported previousy, and (3) a low positronium annihilation fraction f = 0.38 + or 0.19 during the fall of 1979. If positrons are generated by photon-photon collisions of high-energy photons, then the absence of a detected flux above 511 keV in the spring of 1980 may indicate a time delay between positron production and annihilation. 26 references.

The gamma-ray spectrum of the Galactic center region

The HEAO‐3 High Resolution Gamma‐Ray Spectrometer observed the galactic center region in fall 1979 and in the spring of 1980. Variation of the positron annihilation line at 511 keV has been reported previously. The fall1979 observations show a significant high‐energy continuum at energies above 511 keV. The intensity of a possible positronium triplet‐state continuum is found to be less than that expected for direct positron annihilation and positronium decay in an ionized, warm (T≲105 K) plasma; depending on assumption for the shape of the high‐energy continuum spectrum, positronium fractions between 0.0 and 0.75 (at 90% statistical confidence level) are consistent with the observations.

Detection of an X-ray flare in the RS CVn binary Sigma Coronae Borealis

The detection of an X-ray flare in the RS CVn binary Sigma Coronae Borealis with the Monitor Proportional Counter on the Einstein Observatory is described. During the 513 min of observation, an X-ray flare of 208 min duration was detected at a significance level of 26 sigma in the 1.19-10.16 keV band. The rise time of the flare is between 25 and 70 min and the decay time is greater than or equal to 34 min. The X-ray luminosity at the flare maximum is found to be 6 x 10 to the 30th erg/s and the total energy radiated in X-rays during the flare is 2 x 10 to the 34th erg. The energy spectrum in the flaring state is found to be harder (temperature T about 2.5 x 10 to the 7th K) compared to the one observed in the quiescent state (T about 6 x 10 to the 6th K). Applying the coronal loop model, the loop parameters are calculated and compared for the X-ray flares observed in the various RS CVn binaries and the sun. The significance of the differences in the observed and derived parameters of the X-ray flares is briefly discussed.

Gamma-ray and optical observations of the 1979 November 8 solar flare

The solar flare on 1979 November 8 11h 21m 28s UT was observed by the Tel Aviv telescope of the Big Bear Solar Observatory and the High Resolution Gamma-Ray Spectrometer on the High Energy Astronomy Observatory HEAO 3. Photographs in Hα show the development of the flare and a subsequent Moreton wave. Although the flare was not detected with the high spectral resolution germanium detectors, the HEAO C-1 CsI shield detected a statistically significant signal above 80 keV, from 420 to 585 keV, and above 3.8 MeV. The temporal structure of microwave, optical, X-ray, and gamma-ray emission is consistent to within ~1 s with a simultaneous flare response at all energies. There is no evidence for either second-stage acceleration of charged particles (Bai and Ramaty, 1979) or a delay between gamma-ray and X-ray continuum emission due to energy-dependent electron energy loss times (Bai and Ramaty).

X-Ray Telescope For Sounding Rocket-Borne Observations

The X-ray astronomy group at Caltech has developed an X-ray telescope for sounding rocket-borne observations above the Earths atmosphere. The telescope consists of a pair of nested aluminum mirrors, 40.64 cm and 31.65 cm in diameter with a total geometrical collecting area of 200 cm2. The mirror surfaces have been machined at the Y-12 plant of the Oak Ridge National Laboratory using an air bearing spindle lathe and a diamond tool. Design and performance characteristics will be presented. The design of the next generation telescope of 91 cm diameter will be presented.

Evidence for delayed second phase acceleration in solar flares

Twenty‐two (22) solar flares with emission at or above 0.5 MeV have been observed by the HEAO‐3 gamma‐ray spectrometer during the period 1 October 1979 through 1 July 1980. In two of these flares, the peak emission in a band around 0.5 MeV follows the peak of the impulsive hard x‐ray emission at energies greater than 0.1 MeV by as much as 30 seconds. In both of these flares the 0.5 MeV flux risetime was 30–40 seconds followed by a decay time of less than 10 seconds. The onset of the 0.5 MeV flux was not measurably different (<10 seconds) from the onset of the integrated emission greater than 0.1 MeV. The remaining 20 flares gave no indication of a delay in either peak emission or onset time between the high energy and low energy components (<5 seconds), nor were there any decay times shorter than risetimes. Thirteen (13) of the flares had a measurable flux above 3.8 MeV and have been characterized by a two power law fit with an artificial break at 0.5 MeV. The remaining flares were characterized by a single power law up to 0.5 MeV.

Gamma-ray burst observations by the HEAO-3 high-resolution gamma-ray spectrometer

Observations of cosmic gamma‐ray bursts with the JPL High‐Resolution Gamma‐Ray Spectrometer on HEAO‐3 are discussed. Two bursts seen on 1979 November 16 are of particular interest. The first event occurred at 14:16:41 UT and lasted for eight seconds. This event was detected only by the instrument’s five CsI shield segments. The second event occurred 61 sec later, at 14:17:42 UT, and lasted 18 sec. This event was clearly detected by the high‐resolution germanium detectors. Because of the close temporal coincidence of the two events, we consider the possibility that both originated from one celestial source, and that the scanning motion of HEAO, 3 (nominal spin period 20 min) was such as to exclude the first from the (approximately 30° FWHM) field of view of the germanium detectors and include the second. Directional information from the relative response of the shield pieces and Earth occulation constraint are all consistent with this interpretation and high‐resolution spectral data from the second burst a...