29 research outputs found
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
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
.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 Se, Kr and 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 âSe 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