2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/8335The CELESTE atmospheric Cherenkov detector ran until June 2004. It has detected several gamma-ray flares of Mrk 421 since 1999. The new data analysis provides better background rejection. We compare our light curves with X-ray data. We significantly improved our understanding of the atmosphere, and of the optical throughput of the detector. This will allow a spectral measurement for Mrk 421 with smaller uncertainties and a more sensitive search for a signal from Mrk 501.2 pages, 2 figures, proc. of the SF2A Scientific Highlights conf. held in Paris, France, June 2004, eds.: F. Combes, D. Barret, T. Contini, F. Meynadier and L. Pagani, EdP-Sciences Conf. SeriesAstrophysicstext