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Modulation imaging method on the basis of direct restoration technique, which we developed for analyzing space γ-ray data, can produce images with fine angular resolution over a wide field by means of a simple collimated telescope. This method can be used for conducting deep-sky, high-resolution, low-energy γ-ray surveys on board satellites and for making simultaneous space multi-wavelength observations.

In this paper we propose to use the method of iterative calculation to solve directly the imaging equation for image recovery. The same method can be applied to the recovery of one-dimensional spectra. During the iteration suitable constraints are applied to effect nonlinear control over the process. The use of fitting technique in the treatment of the imaging equation suppresses noise and raises sensitivity. Analyses of both Monte Carlo samples and actual high-energy astronomical data showed that the direct method is more sensitive and having greater resolving power than the traditional method, is capable of revealing simultaneously both diffuse and discrete structures in the target object and can be used on data of lower statistical quality. In principle, the direct method can be used in all types of image and spectrum recovery in other fields.

The electron-positron annihilation process in accreting binary systems, typically Cygnus X-3, was investigated. Our Monte Carlo calculation shows that, under certain conditions such systems can emit a rather narrow annihilation line, whose flux and width depend on the intensity of the emitted γ photons, the state, size and temperature distribution of the X-ray halo, and the density and distribution of the electrons in the disk. We also discussed the possibility of observing the line by current experiments including the OSSE detector on board the GRO satellite.

A gamma-ray map of the Galaxy in 40–50 MeV reveals, besides the three sources known at higher energies, four additional sources with intensities comparable to that of the Crab.

In a previous paper [1] we obtained statistically significant evidence for a 39-ms period in the COS-B data of 30–5000 MeV gamma rays in the direction of PSR 1951 + 32. Most of the gamma photons from PSR 1951 + 32 are pulsed and concentrated in a narrow interval of phase. We have examined the partical distribution of gamma ray intensity in the region around the pulsar and estimated the integrated flux to be 4.1 × 10 −7 ph cm −2 s −1 above 100 MeV and 8.2 × 10 −8 ph cm −2 s −1 above 300 MeV.

We present here the result of the hard X spectrum of Cyg X-1 in the 20–200 keV range obtained with a balloon-borne CsI-NaI phoswich telescope launched at Xianhe Balloon Facilities on 1985 Sept 22. The X luminosity in 10–200 keV is estimated to be (1.07 ± 0.08) × 1037 erg/s, which indicates that Cyg X-1 may not be in the normal low state at that time.

We have re-analyzed Einstein Observatory data on CTB 80 using phase folding method. Significant pulsation was found in both the HRI and IPC data with similar phase diagrams at periods near those predicted by the radio observations. An acceleration in PSR 1951+32 during the period October 1979–April 1980 is indicated.

We calculated the absorption of gamma rays of Cygnus X — 3 by the ambient X — ray photons through photon-photon pair production and inverse Compton scattering. Differences in the gamma ray spectrum between the X — ray high state and low state indicate the presence of this absorption.

The hard X-ray phoswich telescope, HAPI-1, is described. It was designed for making observations on board high-flying balloons. The telescope comprises a 145 cm 2 primary crystal of 5 cm thick Cs I(T1), effectively shielded over the lower 2π steradians by a 5 cm thick NaI(T1) crystal and has a field of view of approximately 4° HWHM determined by a graded shield and a collimator. The scintillation pulses originating in CsI and NaI crystals are distinguished by pulse shape discrimination. All sub-systems of the telescope are described. The Crab pulsar was obsserved by HAPI-1 in a balloon flight on 1984 May 23 in the energy range 20 to 200 keV and the observed result is presented.

From an analysis of the data from the gamma-ray satellite COS-B and from radio measurements of CO molecules, it appears probable that the three gamma-ray sources 2CG 036+01, 218-00, 235-01 are either isolated giant molecular clouds or superpositions of clouds unresolved by the detector.