Astrophysique à Haute Energie

The Extreme Physics of Neutron Stars — An observer’s view point

Neutron stars are fantastic cosmic laboratories to study the most extreme physics. Their intense gravitational fields can provide tests of general relativity and other theories of gravitation. Their unmatched magnetic fields permit studies of the interaction between matter and these fields. And their extreme interior densities allow us to probe matter in regimes not accessible to Earth laboratories.  

O2 multi-messenger campaign and future prospects with the SVOM mission

The O2 follow-up campaign of gravitational wave candidate (GW) events was intensive with the collaboration of 95 groups in astronomy and astro-particle physics.  Since the size of the localization error of GW is quite large, the follow-up strategy for finding counterpart of GW alerts is quite complex. However, the joint accomplishment was rewarded with the first multi-messenger probe of the merger of a binary neutron stars (GW170817), an associated electromagnetic counterpart as gamma-ray burst (GRB170817A) and bright multiwavelength isotropic emission.

On-ground multipoint radiation measurement discovering atmospheric photonuclear reactions triggered by lightning discharge in Japan

Energetic radiation associated with thunderstorm activities have been detected by on-ground, airborne, rocket-triggered lightning experiments, as well as in-orbit detectors as terrestrial gamma-ray flashes (TGFs). The high energy emissions, including bremsstrahlung gamma rays with energy extending up to 20 MeV, indicate powerful electron accelerations inside thunderclouds or along lightning discharge paths. We focus on unique characteristics of winter thunderstorms such as lower cloud bases and powerful activities, and started a multipoint mapping observation campaign since 2015.

Solar neutrinos: from MeV to TeV

The observation of solar neutrinos in the late sixties represents an important milestone in (astro-) particle physics. According to theoretical predictions, the Sun may turn out to be an exceptional neutrino factory producing, in addition to the already observed MeV neutrinos from fusion, neutrinos up to TeV energies. I will review the different processes that might lead to a significant signal in neutrino observatories in  the near future.

X-ray spectral index correlations vs mass accretion rate in neutron star and black hole X-ray binaries in their different spectral states. Theory vs observations

I present  details  of observations of neutron star (NS) and black hole (BH) binaries and the first principle theory of X-ray spectral formation in neutron star (NS) and black hole (BH) there.  I show that this model predicts the spectral index correlation vs mass accretion rate  as in the case of NS as well in the BH case.  In BHs the spectral index should increase and then saturate with mass accretion rate, because the index is an inverse  of Comptonization parameter Y and  Y-parameter saturates with the high mass accretion rate in the converging flow onto BH.

Simulating the interaction between non-thermal particles and the magnetic field in astrophysical shocks

Cosmic rays are charged particles that have been accelerated to high velocities as they cross astrophysical shocks. This acceleration process involves repeated interactions between the particles and the local magnetic field, which not only influence the velocity of the particles, but the morphology of the magnetic field, and therefore the shock structure, as well. 

Hunting Gravitational Waves using Gamma-Ray Burst and High Energy Neutrinos as triggers

The Gamma Ray Bursts [GRB] and high energy neutrinos [HEN] are thought to be produced by Gravitational Waves [GW] progenitors. The collaboration LIGO/Virgo is using GRB and HEN as triggers in order to find Gravitational Waves at low-latency and offline with a refined analysis. This includes the unreleased GRB and HEN that were found offline by Fermi GBM and Icecube. We will introduce the different methods used to achieve this goal that were used for the first run offline analysis of LIGO, triggering GRBs and are now used for the second one.

High-energy neutrinos, cosmic rays, and gamma rays from gamma-ray bursts

Ultra-high-energy cosmic rays and high-energy astrophysical neutrinos are
routinely detected, but their sources remain unknown.  Gamma-ray bursts
(GRBs) have long been considered attractive candidate sources.  Recently, the
lack of neutrinos detected in coincidence with known GRBs has motivated
revisions of the multi-messenger emission mechanism --- gamma rays, cosmic rays,
neutrinos --- from within the GRB jet.  By embedding this revised mechanism in a
simulation of multiple emission regions within the jet, we obtain a robust

Analyzing diffuse gamma rays to understand the physics of cosmic-ray propagation

I present a broad overview of the current cosmic-ray (CR) transport modeling, and discuss several recent results obtained with the DRAGON code. Several anomalies in the measured CR spectra and gamma-ray data are discussed with particular focus on: the positron excess, the hint of an antiproton excess, the proton and helium spectral breaks, the gamma-ray GeV excess, which may point to either new classes of sources, non-standard propagation models, or new physics.


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