Search

We have examined the spectra of 38 γ‐ray bursts observed by the Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission (SMM) satellite for evidence of a nuclear contribution to the high energy flux. A sum of spectra from the nine bursts with detectable flux ≳4 MeV suggests but does not require a drop‐off above 7 MeV. A cutoff between 7 and 8 MeV is consistent with a high energy spectrum dominated by nuclear lines.

The Gamma‐Ray Spectrometer (GRS) on NASA’s Solar Maximum Mission satellite detected gamma‐ray line emission from the decay of 56Co in SN 1987A beginning in 1987 August.1,2 Balloon‐borne experiments have also reported the detection of these lines in 1987 October,3,4 December,5 and 1988 January,6 and excesses consistent with lines in 1987 Novemver.7,8 Since the initial report we have continued to monitor the emission from the supernova with the GRS, and report here observations through 1988 April 6. The average fluxes for the total observation period (1987 August 1 to 1988 April 6) are (6.6±2.0)×10−4 and (6.4±1.7)×10−4 photons–cm−2–s−1 for the 847 and 1238 keV lines, respectively. The quoted errors represent a combination of statistical and systematic uncertainties. There has been no marked increase in the intensity of either line since the end of October, and the data are consistent with a constant flux since August 1. The best‐fit energies for the two lines are 840±6 and 1239±10 keV.

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.

The SMM gamma ray experiment has observed 60 gmma‐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. Our detailed search was limited to narrow lines (

Positron annihilation radiation has been observed from the 21 June 1980 and 3 June 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±3.3 γ/cm2 and 103±8 γ/cm2, respectively. Measurement of the line width allows us to set an upper limit to the temperature in the annihilation region of 3×106 °K. The time dependence of the 0.511 MeV line during the 21 June 1980 flare is consistent with Ramaty et al.’s calculations for positrons created in the decay of radioactive nuclei. The time dependence of 0.511 MeV line for the 3 June 1982 flare is more complex and requires more detailed study.

Long‐term temporal variations in the various components of the background radiation detected by the gamma‐ray spectrometer on the Solar Maximum Mission are presented. The SMM gamma‐ray spectrometer was launched in February, 1980 and continues to operate normally. The extended period of mission operations has provided a large data base in which it is possible to investigate a variety of environmental and instrumental background effects. In particular, several effects associated with orbital precession are introduced and discussed.

We present preliminary results of an analysis of data collected with the Solar Maximum Mission Gamma‐Ray Spectrometer (GRS) in an effort to provide limits on the spatial distribution of Galactic 26Al radiation. This analysis utilizes a new technique for applying the GRS data to extra‐solar observations. Here we describe this technique and present data collected using four passages of the Galactic center region through the GRS field‐of‐view. The data are compared with three models: one representing a point source at the Galactic Center; one a distribution following that of Galactic CO; and a third which follows the distribution of novae in the Galaxy. Preliminary analysis indicates that the data are qualitatively in better agreement with the diffuse models.

We discuss broad‐band continuum spectroscopy of 17 gamma‐ray bursts above 0.3 MeV. The spectra were fitted by 3 trial functions, none of which provided an adequate fit to all the spectra. Most were too hard for a thermal bremsstarhlung function. Harder functional forms, such as thermal synchrotron or power‐law, provide better fits for most of the spectra. The strong emission observed above 1 MeV raises some interesting theoretical questions.