Gamma-ray astronomy from 10 to 100 GeV

A recently completed Monte Carlo calculation of the light distributions from air showers initiated by protons and by gamma-rays in the (10:1000)GeV region suggests a significant difference in the two types of showers at the lowest energies. At the same time, it shows that there is sufficient light generated by gamma-ray primaries of energy as low as 20 GeV to give an effective detection area of about 1000 m2. By exploiting the differences between the two types of showers, an atmospheric Cerenkov experiment can be devised such that the flux sensitivity for (10:100)GeV gamma-rays may be 10:30 times less than that which would be expected by extrapolating from higher energies by using conventional techniques (e.g. by increasing the mirror area). One detector system which would effectively exploit this feature is described. (author)