863 research outputs found
Intensity Correlation between Observations at Differrent Wavelengths for Mkn 501 in 1997
The CAT imaging telescope on the site of the former solar plant Th'emis in
southern France observed gamma-rays from the BL Lac object Mkn501 above 250 GeV
for more than 60 usable hours on-source from March to October 1997. This source
was in a state of high activity during all this period. By studying the
correlation between the photons of different energies detected by the CAT
imaging telescope and by the ASM/RXTE experiment (1.3-12.0 keV) on board the
Rossi X-Ray Timing Explorer, we may constrain the mechanisms which could lead
to the emission of these photons.Comment: Proceedings of the 19th Texas Symposium. 8 pages, 7 figure
Active Galactic Nuclei as High Energy Engines
Active Galactic Nuclei are considered as possible sites of cosmic ray
acceleration and some of them have been observed as high energy gamma ray
emitters (Blazars). There naturally comes an appealing idea that the
acceleration of the highest energy cosmic rays in the AGNs has a signature in
the form of gamma ray emission and high energy neutrino emission through the
collisions of very high energy protons with soft photons. Moreover it is often
said that electrons cannot reach enough energy through Fermi acceleration to
account for the highest energy photons observed with ground Cerenkov
telescopes. In this paper, we discussed these points and show that the fast
variability of the flares recently observed rules out the assumption of a Fermi
acceleration of protons. We show that Fermi acceleration of electrons is enough
to account for the gamma spectra, their shape, cut-off and their variability.
Moreover the spectral break is nicely explained by invoking an gamma-ray
photosphere. Nevertheless we give estimates of the high energy cosmic ray
generation in AGNs and of the resultant neutrino flux, that turns out to be
very sensitive to the spectral index of the proton distribution.Comment: 17 pages, 1 figure, accepted for publication in Astrophysics
Particle
IMACLIM-R: a modelling framework to simulate sustainable development pathways
To assess the sustainability of future development pathways requires models to compute long-run Economy-Energy-Environment scenarios. This paper presents the IMACLIM-R framework, aimed at investigating climate, energy and development inter-related issues. The model was built in an attempt to address three methodological challenges: to incoporate knowledge from economics and engineering sciences, to support the dialogue with and between stakeholders, to produce scenarios with a strong consistency, concerning especially the interplay between development patterns, technology and growth. These goals led to the development of a recursive structure articulating a static general equilibrium framework including innovative features and sectorspecific dynamic modules now concerning energy, transportation and industry. This paper provides the general rationale of the model and the description of all its components.
IMACLIM-R: a modelling framework to simulate sustainable development pathways
International audienceTo assess the sustainability of future development pathways requires models to compute long-run Economy-Energy-Environment scenarios. This paper presents the IMACLIM-R framework, aimed at investigating climate, energy and development inter-related issues. The model was built in an attempt to address three methodological challenges: to incoporate knowledge from economics and engineering sciences, to support the dialogue with and between stakeholders, to produce scenarios with a strong consistency, concerning especially the interplay between development patterns, technology and growth. These goals led to the development of a recursive structure articulating a static general equilibrium framework including innovative features and sectorspecific dynamic modules now concerning energy, transportation and industry. This paper provides the general rationale of the model and the description of all its components
Inventaire printanier d'une frayère multispécifique : l'ichtyofaune des rapides de la rivière Gatineau, Québec
Un inventaire ichtyologique printanier a été réalisé dans la rivière Gatineau, dans le premier rapide à l’amont de son embouchure dans la rivière des Outaouais, pour établir la chronoséquence d’utilisation du site par les espèces s’y reproduisant, dont trois espèces de chevaliers. L’échantillonnage des rapides a permis de capturer 2388 poissons répartis en 13 familles et 39 espèces, dont six ayant fait l’objet d’une évaluation par le COSEPAC. Seize espèces étaient en état de se reproduire lors de l’échantillonnage. Nous avons observé une reproduction plus ou moins simultanée pour le Chevalier blanc et le Chevalier rouge, suivie de celle du Chevalier de rivière. Également, pour ces trois espèces, nous avons observé la capture des mâles de stade V plus tôt que les femelles, et nous les retrouvons en plus grand nombre. Ceci pourrait s’expliquer du fait que les mâles précèdent les femelles sur les frayères, que celles-ci sont reconnues pour rester très peu de temps sur les sites de fraie et qu’un minimum de deux mâles par femelle est requis pour la reproduction. Cette étude démontre que les rapides de la rivière Gatineau doivent être protégés puisqu’ils sont habités par trois espèces qui ont obtenu un statut spécial du COSEPAC (Menacée: Fouille-roche gris; situation préoccupante : Lamproie du nord et Chevalier de rivière) en plus de constituer une frayère multispécifique importante
An inhomogeneous jet model for the rapid variability of TeV blazars
We present a new time-dependent inhomogeneous jet model of non-thermal blazar
emission, which reproduces the entire spectral energy distribution together
with the rapid gamma-ray variability. Ultra-relativistic leptons are injected
at the base of a jet and propagate along the jet structure. We assume
continuous reacceleration and cooling, producing a relativistic
quasi-maxwellian (or "pile-up") particle energy distribution. The synchrotron
and Synchrotron-Self Compton jet emissivity are computed at each altitude.
Klein-Nishina effects as well as intrinsic gamma-gamma absorption are included
in the computation. Due to the pair production optical depth, considerable
particle density enhancement can occur, particularly during flaring states.
Time-dependent jet emission can be computed by varying the particle injection,
but due to the sensitivity of pair production process, only small variations of
the injected density are required during the flares. The stratification of the
jet emission, together with a pile-up distribution, allows significantly lower
bulk Lorentz factors, compared to one-zone models. Applying this model to the
case of PKS2155-304 and its big TeV flare observed in 2006, we can reproduce
simultaneously the average broad band spectrum of this source as well as the
TeV spectra and TeV light curve of the flare with bulk Lorentz factor lower
than 15
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