A new analysis strategy for detection of faint gamma-ray sources with Imaging Atmospheric Cherenkov Telescopes

A new background rejection strategy for gamma-ray astrophysics with stereoscopic Imaging Atmospheric Cherenkov Telescopes (IACT), based on Monte Carlo (MC) simulations and real background data from the H.E.S.S. [High Energy Stereoscopic System, see [1].] experiment, is described. The analysis is based on a multivariate combination of both previously-known and newly-derived discriminant variables using the physical shower properties, as well as its multiple images, for a total of eight variables. Two of these new variables are defined thanks to a new energy evaluation procedure, which is also presented here. The method allows an enhanced sensitivity with the current generation of ground-based Cherenkov telescopes to be achieved, and at the same time its main features of rapidity and flexibility allow an easy generalization to any type of IACT. The robustness against Night Sky Background (NSB) variations of this approach is tested with MC simulated events. The overall consistency of the analysis chain has been checked by comparison of the real gamma-ray signal obtained from H.E.S.S. observations with MC simulations and through reconstruction of known source spectra. Finally, the performance has been evaluated by application to faint H.E.S.S. sources. The gain in sensitivity as compared to the best standard Hillas analysis ranges approximately from 1.2 to 1.8 depending on the source characteristics, which corresponds to an economy in observation time of a factor 1.4 to 3.2.Comment: 26 pages, 13 figure

Status of Very High Energy gamma-ray Astronomy as of early 2008

Data obtained in the very high energy gamma-ray band with the new generation of imaging telescopes, in particular through the galactic plane survey undertaken by H.E.S.S., low threshold observations with MAGIC and more recently by operation of VERITAS, have revealed dozens of galactic and extragalactic sources, providing a wealth of information on a variety of high energy acceleration sites in our universe. Also, the water Cherenkov instrument Milagro has provided several extended sources after seven years of data integration. An overview of these results with focus on some of the most recent highlights is given.Comment: 8, pages, 1 figure, Proceedings of the 3rd Workshop for a Very large volume neutrino telescope for the Mediterranean Sea (VLVnT08) Toulon, April 22-24 2008, (to be published in Nucelar Instruments and Methods A

Gravitational effects of free-falling quantum vacuum

International audienceWe present a model that builds ``dark matter"-like halo density profiles from free-falling zero-point vacuum fluctuations. It does not require a modification of Newton's laws, nor the existence of as-yet-undiscovered dark matter particles. The 3D halos predicted by our model are fully constrained by the baryonic mass distribution, and are generally far from spherical. The model introduces a new fundamental constant of vacuum, T, having the dimensions of time. We deduce the associated formalism from some basic assumptions, and adjust the model successfully on several spiral galaxy rotation data while comparing our results to the existing analyses. We believe our approach opens up a new paradigm that is worth further exploration, and that would benefit from checks relating to other phenomena attributed to dark matter at all time and distance scales. Following such a program would allow the present model to evolve, and if successful it would make vacuum fluctuations responsible for the typical manifestations of dark matter

Gravitational effects of free-falling quantum vacuum

International audienceWe present a model that builds ``dark matter"-like halo density profiles from free-falling zero-point vacuum fluctuations. It does not require a modification of Newton's laws, nor the existence of as-yet-undiscovered dark matter particles. The 3D halos predicted by our model are fully constrained by the baryonic mass distribution, and are generally far from spherical. The model introduces a new fundamental constant of vacuum, T, having the dimensions of time. We deduce the associated formalism from some basic assumptions, and adjust the model successfully on several spiral galaxy rotation data while comparing our results to the existing analyses. We believe our approach opens up a new paradigm that is worth further exploration, and that would benefit from checks relating to other phenomena attributed to dark matter at all time and distance scales. Following such a program would allow the present model to evolve, and if successful it would make vacuum fluctuations responsible for the typical manifestations of dark matter

Gravitational effects of free-falling quantum vacuum

International audienceWe present a model that builds ``dark matter"-like halo density profiles from free-falling zero-point vacuum fluctuations. It does not require a modification of Newton's laws, nor the existence of as-yet-undiscovered dark matter particles. The 3D halos predicted by our model are fully constrained by the baryonic mass distribution, and are generally far from spherical. The model introduces a new fundamental constant of vacuum, T, having the dimensions of time. We deduce the associated formalism from some basic assumptions, and adjust the model successfully on several spiral galaxy rotation data while comparing our results to the existing analyses. We believe our approach opens up a new paradigm that is worth further exploration, and that would benefit from checks relating to other phenomena attributed to dark matter at all time and distance scales. Following such a program would allow the present model to evolve, and if successful it would make vacuum fluctuations responsible for the typical manifestations of dark matter

Refraction of light by light in vacuum

6 pages, 4 figuresInternational audienceIn very intense electromagnetic fields, the vacuum refractive index is expected to be modified due to non linear QED properties. Up to now, these predictions are tested by searching phase shifts in the propagation of polarized light through uniform magnetic fields. We propose a new approach which consists in producing a vacuum index gradient and send a light beam trough it in order to detect its angular deviation. The vacuum index gradient, similar to a "prismatic vacuum", is created by the interaction of two very intense and ultra short laser pulses, used as pump pulses. At the maximum of the index gradient, the deflection angle of the probe pulse is estimated to be $2 \ 10^{-13} \times (\frac{w_0}{10 \mu\mathrm{m}})^{-3} \times \frac{I}{1 \mathrm{J}}$ radians, where $I$ is the total energy of the two pump pulses and $w_0$ is the minimum waist (fwhm) at the interaction area of the two pump pulses. Assuming the most intense laser pulses attainable by the LASERIX facility ($I = 25$ J, 30 fs fwhm duration, 800 nm central wavelength) and assuming a minimum waist of $w=10 \mu\mathrm{m}$ (fwhm) (corresponding to an intensity of the order of $10^{21}$ W/cm$^2$), the expected deflection angle is about $5 \ 10^{-12}$ radians at the maximum of the index gradient. We propose to measure it with a Sagnac interferometer

HAP-Fr, a pipeline of data analysis for the HESS-II experiment

International audienc