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Abstract. It has been suggested that young pulsars, with ages less than a million years, are possible counterparts of some of the Galactic unidentified gamma-ray sources detected by the EGRET instrument on-board the Compton Gamma Ray Observatory. In this work, we compare different aspects of the EGRET unidentified (EUI) source distribution in the Galactic plane with those of the pulsar distribution. An EUI source Log N-Log S analysis is presented and compared with the Galactic radio pulsar Log N-Log S distribution. A number of systematic effects that could introduce errors to the EGRET Log N-Log S relation are discussed. A two-point angular correlation analysis of the EUI sources and Galactic pulsars is performed. We find that the global distribution properties of the plane EUI sources do not follow those of the young pulsar population. We conclude that even though a fraction of the EUI sources may have young pulsar counterparts, the majority of them follow a distribution that is similar to the molecular cloud distribution in nearby spiral arms.

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Angle and energy distributions are reported here for gamma rays from ground level to 3.5 g/cm² residual atmosphere at energies of 2 to 25 MeV and zenith angles of 0° to 50° and 180° to 130°. They complement the previous results of Ryan et al. (1977) for altitudes above 100 g/cm². The observations were made with the University of California, Riverside (UCR), double Compton scatter telescope from a balloon launched from Palestine, Texas, geomagnetic cut‐off of 4.5 GV, on May 13, 1975. The ground level measurements were made at Riverside, California, at 1000‐g/cm² residual atmosphere, geomagnetic cut‐off of 5.4 GV, on July 21, 1977. Growth curves for downward‐moving gamma rays have pronounced maxima at 160±30 g/cm² residual atmosphere, while those for upward‐moving gamma rays are essentially constant at altitudes above the Pfotzer maximum. Below about 300 g/cm² both the downward and the upward fluxes decrease with average e‐folding depths of 192±15 and 179±12 g/cm², respectively. The ratio of the downward‐ to upward‐moving gamma rays near the vertical is 17±5, independent of depth below the Pfotzer maximum. The energy variation, E−1.1, of the downward‐moving gamma rays is flatter than the E−1.8 of the upward moving ones at all depths below 100 g/cm². All zenith angle distributions show peaks toward the horizon. Above the Pfotzer maximum the downward flux decreases more rapidly away from the horizon than the upward flux, while below the converse is true. The azimuth angle distributions at 4.0 g/cm² show northward anisotropies that increase with energy from 3.9±0.9% at 2–10 MeV to 7.0±2.3% at 10–25 MeV.

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