A. Djannati-Ataï

The quantum vacuum as the origin of the speed of light

We show that the vacuum permeability μ0 and permittivity ε0 may originate from the magnetization and the polarization of continuously appearing and disappearing fermion pairs. We then show that if we simply model the propagation of the photon in vacuum as a series of transient captures within these ephemeral pairs, we can derive a finite photon velocity. Requiring that this velocity is equal to the speed of light constrains our model of vacuum. Within this approach, the propagation of a photon is a statistical process at scales much larger than the Planck scale. Therefore we expect its time of flight to fluctuate. We propose an experimental test of this prediction.

Discovery of new TeV supernova remnant shells in the Galactic plane with H.E.S.S.

Supernova remnants (SNRs) are prime candidates for efficient particle acceleration up to the knee in the cosmic ray particle spectrum. In this work we present a new method for a systematic search for new TeV-emitting SNR shells in 2864 hours of H.E.S.S. phase I data used for the H.E.S.S. Galactic Plane Survey. This new method, which correctly identifies the known shell morphologies of the TeV SNRs covered by the survey, HESS J1731-347, RX 1713.7-3946, RCW 86, and Vela Junior, reveals also the existence of three new SNR candidates. All three candidates were extensively studied regarding their morphological, spectral, and multi-wavelength (MWL) properties. HESS J1534-571 was associated with the radio SNR candidate G323.7-1.0, and thus is classified as an SNR. HESS J1912+101 and HESS J1614-518, on the other hand, do not have radio or X-ray counterparts that would permit to identify them firmly as SNRs, and therefore they remain SNR candidates, discovered first at TeV energies as such. Further MWL follow up o...

Gammapy - A prototype for the CTA science tools

Gammapy is a Python package for high-level gamma-ray data analysis built on Numpy, Scipy and Astropy. It enables us to analyze gamma-ray data and to create sky images, spectra and lightcurves, from event lists and instrument response information, and to determine the position, morphology and spectra of gamma-ray sources. nSo far Gammapy has mostly been used to analyze data from H.E.S.S. and Fermi-LAT, and is now being used for the simulation and analysis of observations from the Cherenkov Telescope Array (CTA). We have proposed Gammapy as a prototype for the CTA science tools. This contribution gives an overview of the Gammapy package and project and shows an analysis application example with simulated CTA data.

Refraction of light by light in vacuum

AbstractIn very intense electromagnetic fields, the vacuum refractive index is expected to benmodified due to nonlinear quantum electrodynamics (QED) properties. Several experimentalntests using high intensity lasers have been proposed to observe electromagneticnnonlinearities in vacuum, such as the diffraction or the reflection of intense lasernpulses. We propose a new approach which consists in observing the refraction, i.e. thenrotation of the waveplanes of a probe laser pulse crossing a transverse vacuum indexngradient. The latter is produced by the interaction of two very intense and ultra shortnlaser pulses, used as pump pulses. At the maximum of the index gradient, the refractionnangle of the probe pulse is estimated to be 0.2xa0×xa0(w0/10xa0μm)-3xa0×xa0I/1Jxa0prad, where I is the total energy of the two pump pulses andnw0 is the minimum waist (fwhm) at theninteraction area. Assuming the most intense laser pulses attainable by the LASERIXnfacility (I =n25xa0J, 30xa0fs fwhm duration, 800xa0nm central wavelength) and assuming anminimum waist of w = 10nμm (fwhm) (corresponding to an intensity of thenorder of 1021xa0W/cm2), the expected maximum refraction angle is aboutn5xa0prad. An experimental setup, using a Sagnac interferometer, is proposed to perform thisnmeasurement.Graphical abstract

A closer look at HESS J1837-069 following the pulsar discovery

The gamma‐ray source HESS J1837‐069 was discovered during the first scan of the galactic plane, and was classified as an unidentified source, possibly associated with AX J1838.0‐0655. Recently, an energetic 23 kyr pulsar was discovered in coincidence with the ASCA source. We present a preliminary analysis of a larger HESS data set which reveals finer morphology and spectral details. We discuss the pulsar wind nebula (PWN) interpretation of the gamma‐ray source in view of the characteristics of other very high energy (VHE) emitting pulsar wind nebula.

Can the apparent expansion of the universe be attributed to an increasing vacuum refractive index

H.A. Wilson, then R.H. Dicke, proposed to describe gravitation by a spatial change of the refractive index of the vacuum around a gravitational mass. Dicke extended this formalism in order to describe the apparent expansion of the universe by a cosmological time dependence of the global vacuum index. In this paper, we develop Dicke’s formalism. The metric expansion in standard cosmology (the time-dependent scale factor of the Friedmann–Lemaître curved spacetime metric) is replaced by a flat and static Euclidean metric with a change with time of the vacuum index. We show that a vacuum index increasing with time produces both the cosmological redshift and time dilation, and that the predicted evolution of the energy density of the cosmological microwave background is consistent with the standard cosmology. We then show that the type Ia supernovæ data, from the joint SDSS-II and SNLS SNe-Ia samples, are well modeled by a vacuum index varying exponentially as

Evidence for VHE emission from SNR G22.7-0.2 region with H.E.S.S

n(t)=exp(t/tau _0)

Reply to the Comment on: The quantum vacuum as the origin of the speed of light

n(t)=exp(t/τ0), where