Evidence for transfer followed by breakup in 7Li + 65Cu

The observation of a large cross-section for the alpha + d channel compared to breakup into the alpha + t channel from an exclusive measurement for the 7Li+65Cu system at 25 MeV is presented. A detailed analysis of the angular distribution using coupled channels Born approximation calculations has provided clear evidence that the observed alpha + d events arise from a two step process, i.e. direct transfer to the 2.186 MeV (3+) resonance in the alpha + d continuum of 6Li followed by breakup, and are not due to final state interaction effects.Comment: 12 pages, 3 figures, To be published in Phys. Letts.

Spectrum and Variability of Mrk501 as observed by the CAT Imaging Telescope

The CAT Imaging Telescope has observed the BL Lac object Markarian 501 between March and August 1997. We report here on the variability over this time including several large flares. We present also preliminary spectra for all these data, for the low emission state, and for the largest flare.Comment: 4 pages, 4 figures, Late

Detection of Vhe Gamma-Rays from MRK 501 with the Cat Imaging Telescope

The CAT imaging telescope on the site on the former solar plant Themis has been observing gamma-rays from Mrk501 above 220 GeV in March and April 1997. This source is shown to be highly variable and the light curve is presented. The detected gamma-ray rate for the most intense flare is in excess of 10 per minute.Comment: 5 pages, 4 figures, Tex, contribution to 25th ICRC Durba

Measurement of the Crab Flux Above 60 GeV with the CELESTE Cherenkov Telescope

We have converted the former solar electrical plant THEMIS (French Pyrenees) into an atmospheric Cherenkov detector called CELESTE, which records gamma rays above 30 GeV (7E24 Hz). Here we present the first sub-100 GeV detection by a ground based telescope of a gamma ray source, the Crab nebula, in the energy region between satellite measurements and imaging atmospheric Cherenkov telescopes. At our analysis threshold energy of 60 +/- 20 GeV we measure a gamma ray rate of 6.1 +/- 0.8 per minute. Allowing for 30% systematic uncertainties and a 30% error on the energy scale yields an integral gamma ray flux of I(E>60 GeV) = 6.2^{+5.3}_{-2.3} E-6 photons m^-2 s^-1. The analysis methods used to obtain the gamma ray signal from the raw data are detailed. In addition, we determine the upper limit for pulsed emission to be <12% of the Crab flux at the 99% confidence level, in the same energy range. Our result indicates that if the power law observed by EGRET is attenuated by a cutoff of form e^{-E/E_0} then E_0 < 26 GeV. This is the lowest energy probed by a Cherenkov detector and leaves only a narrow range unexplored beyond the energy range studied by EGRET.Comment: 34 pages, accepted by the Astrophysical Journa

PARTICULAR MULTINUCLEON TRANSFER PROCESS IN THE 7Li + 197Au REACTION FOR GRAZING CONDITIONS

L'émission prépondérante de particules alpha et de tritons dans la réaction 7Li +197Au ne provient pas d'une dissociation directe du projectile. Les particules sont émises à partir d'un système en rotation quasi lié formé par la cible et la structure en agrégats la moins liée du projectile. Ce mécanisme se produit essentiellement lorsque le projectile est dans le voisinage de la cible avec une vitesse relative négligeable.The preponderant emission of alpha particles and tritons in 7Li + 197Au cannot be accounted for by a projectile break-up hypothesis. The particles are emitted from a quasi-bound rotating system formed by the target and the less bound cluster-structure of the projectile. This mechanism essentially occurs when the projectile is in the vicinity of the target with a negligible relative velocity