Abstract
High energy gamma rays were observed in the energy region 3-30 TeV at the atmospheric depth of 5.5 g/cm2 with balloon-borne emulsion chambers. The long-duration balloon flights (JACEE-7 and -8) were carried out in 1987 and 1988 from Alice Springs, Australia, to South America for about 120-150 hours. The observed gamma ray spectrum can be fitted to a single power spectrum.
I(>E) = (6.0 \pm 1.0) \times 10^{-8} (E/TeV)^{1.74 \pm 0.22} /cm^2 s sr.
Astrophysical components are examined by subtracting those arising from pi0 to 2 gamma decay in the 5.5 g/cm2 atmospheric overburden. These terrestrial components were directly examined and calculated by detecting gamma-ray pairs in the detector. The resulting intensity (upperbound) for astrophysical gamma-rays is obtained as I(E >= 3 TeV) <= 1.10 x 10^-9 cm2 s sr. Comparison with low energy satellite data from SAS-2, COS-B and EGRET suggest that the present JACEE data does not support a very hard differential spectrum E^-beta with an index of beta <= 2.0. It does not preclude a possibility of beta approximately 2.2 to 2.3 for the galactic gamma rays up to about 10 TeV.