The Universe Viewed in Gamma-Rays 1 The Crab Nebula and Mkn 421 High-Energy Gamma-Ray Spectra from CELESTE Observations in 1999-2000

This is the first report on spectral measurements from 50 GeV for the Crab nebula and from 70 GeV for the blazar Markarian 421. Both sources were detected by the CELESTE experiment in 1999-2000. Here we present the energy measurement and spectral reconstruction methods. The energy resolution is shown to smoothly vary with energy, with a mean value of ∼20% above the detection threshold. Preliminary spectra are presented and compared with those obtained quasi-simultaneously above 300 GeV by the CAT imaging telescope.