The spectrum of the diffuse isotropic component of cosmic X-rays over the 13-180 keV range was determined by the UCSD/MIT Hard X-Ray and Gamma-Ray instrument (HEAO A4) on the High Energy Astronomical Observatory-1 (HEAO-1). The instrument consists of a complex of actively shielded and collimated scintillation counters, including the Low Energy Detector set from which the data reported here were obtained. These data join smoothly with the spectrum at lower energies reported by the GSFC HEAO A2 instrument and with that measured to 400 keV by the HEAO A4 Medium Energy Detectors. The HEAO data set also joins the recent results from COMPTEL on the Compton Gamma-Ray Observatory in the 1-10 MeV range, which failed to confirm the existence of an "MeV bump" in this range. Although the spectrum over the entire range 3 keV ≤ E ≤ 100 GeV can be fit by a simple empirical analytic expression, the origin is likely due to a number of distinct source components. The prevailing idea for the origin is that the hard X-ray spectrum is due to X-rays from various AGN components, particularly Seyfert galaxies extending to cosmological distances, and that the low energy gamma-rays may be due to emission from type 1a Supernovae, also integrated to cosmological distances. The higher energy gamma-ray spectrum defined by EGRET, also on the CGRO, may be due to unresolved gamma-ray emitting blazars. Models of production by these source components, extrapolated to the present epoch, must reproduce the observationally derived spectrum.

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We present soft-ray observations by the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (GRO) of the transient X-ray binary pulsar A0535+26. The observations were made 1994 February 8{17, immediately prior to the peak of a giant outburst. The phaseaveraged spectrum is complex and cannot be described by a single-component model. We nd that structure in the spectrum above 100 keV can best be modeled by an absorption feature near 110 keV, which we interpret as the signature of cyclotron resonant scattering. Because of OSSE's 45-keV threshold, we are unable to make a de nitive statement on the presence of a 55-keV absorption line; however we can conclude that if this line does exist, it must have a smaller optical depth than the line at 110 keV. A rst harmonic (= fundamental) cyclotron resonance at 110 keV corresponds to a magnetic eld strength at the surface of the neutron star of 1 10 13 G (5 10 12 G if the rst harmonic is at 55 keV).

The Oriented Scintillation Spectrometer Experiment OSSE on board the COMPTON Gamma Ray Observatory observed the 1991 June 4 X12+ solar are, one of the most intense nuclear gamma-ray line ares observed to date. Using these OSSE observations, we h a v e derived time pro les of the various components of gamma-ray emission and obtained information about the accelerated particle spectra and composition and about the ambient plasma at the are site. The main results are: 1 the nuclear reactions associated with the impulsive phase of the are continued for at least 2 hours and resulted from ions that were probably continuously accelerated rather than impulsively accelerated and trapped; 2 the total energy in these accelerated ions exceeded the energy in 0.1 MeV electrons; 3 the accelerated proton ratio was closer to 0.5 than to 0.1; 4 there is evidence for a decrease of the accelerated heavy ion-to-proton ratio as the are progressed 5 there is evidence for a temporal change in the composition of the are plasma; 6 the ratio of electron bremsstrahlung to the ux in narrow-ray lines decreased as the are progressed; 7 the high-energy 16 MeV component of the electron spectrum was much more impulsive than the lower-energy MeV component; 8 a model-dependent upper limit of 2.3 10 ,5 was obtained for the photospheric 3 He H abundance ratio; and 9 energetic ions may h a v e been present for several hours prior to and following the impulsive phase of the are.

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