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

The Crab Nebula and Pulsar between 500 GeV and 80 TeV: Observations with the HEGRA stereoscopic air Cherenkov telescopes

The Crab supernova remnant has been observed regularly with the stereoscopic system of 5 imaging air Cherenkov telescopes that was part of the High Energy Gamma Ray Astronomy (HEGRA) experiment. In total, close to 400 hours of useful data have been collected from 1997 until 2002. The spectrum extends up to energies of 80 TeV and is well matched by model calculations in the framework of inverse Compton scattering of various seed photons in the nebula including for the first time a recently detected compact emission region at mm-wavelengths. The observed indications for a gradual steepening of the energy spectrum in data is expected in the inverse Compton emission model.The average magnetic field in the emitting volume is determined to be $(161.6\pm0.8mathrm{stat}\pm18_\mathrm{sys}) \mu$G. The presence of protons in the nebula is not required to explain the observed flux and upper limits on the injected power of protons are calculated being as low as 20 % of the total spin down luminosity for bulk Lorentz factors of the wind in the range of $10^4-10^6$.The position and size of the emission region have been studied over a wide range of energies. The position is shifted by 13\arcsec to the west of the pulsar with a systematic uncertainty of 25\arcsec. No significant shift in the position with energy is observed. The size of the emission region is constrained to be less than 2\arcmin at energies between 1 and 10 TeV. Above 30 TeV the size is constrained to be less than 3\arcmin.No indications for pulsed emission has been found and upper limits in differential bins of energy have been calculated reaching typically 1-3 % of the unpulsed component.Comment: 53 pages, 12 figures. Accepted for publication in Astrophysical Journa

Characterization of solids transferred into sewer trunks during wet weather

International audienceThe paper describes the choice of parameters used to characterise sewer sediments in trunk sewers. Different sampling and measurement methods are compared for a number of sites. The sampling arrangement in the BEQUIGNEAUX retention basin, situated in Bordeaux, is described as an example of the methods used. The first results of this study are reported in terms of size, vertical settling velocity and density of suspended solids. There is also a report on the reduction in pollution obtained by settlement of solids.The paper describes the choice of parameters used to characterise sewer sediments in trunk sewers. Different sampling and measurement methods are compared for a number of sites. The sampling arrangement in the BEQUIGNEAUX retention basin, situated in Bordeaux, is described as an example of the methods used. The first results of this study are reported in terms of size, vertical settling velocity and density of suspended solids. There is also a report on the reduction in pollution obtained by settlement of solids

Beta-delayed proton emission from the proton-rich isotopes 67^{67}Se, 71^{71}Kr and 75^{75}Sr

In an experiment at the SISSI/LISE facility of GANIL, we produced proton-rich isotopes in the selenium-to-strontium region by projectile fragmentation of a 78Kr primary beam at 73 MeV/nucleon. The emission of P-delayed protons from h7Se, 7'Kr, and 75Sr was observed for the first time and the corresponding branching ratios were determined. The proton energy spectra were compared to predictions of a statistical model. The half-lives of 67 Se, 7' Kr, and 75Sr were deduced from the time characteristics of the observed proton activity. The half-life of 75Sr was measured for the first time. For “Se and 7'Kr, the obtained half-lives are compared to previous measurements

New isotopes from ^{78}kr fragmentation and the ending point of the astrophysical rapid-proton-capture process

In an experiment at the SISSI/LISE facility of GANIL, we used the projectile fragmentation of a 78Kr primary beam at 73 MeV/nucleon to produce new isotopes of astrophysical interest. We obtained clear evidence for the existence of the five new isotopes 60Ga, 64As, 69,70Kr, and 74Sr. However, we did not find any evidence for 69Br, whereas comparable nuclei were observed with more than 1000 counts. The isotope 69Br is thus deduced to be a proton-unbound nucleus with a half-life shorter than about 100 ns. The influence of these results on our understanding of the astrophysical RP process is discussed