Extreme Universe

The high-energy astrophysics is characterized mainly by the study of objects called compact: white dwarfs, neutron stars and black holes, as well as events taking place in their vicinity. This theme emerged in the Astronomy Department of the University of Geneva in 1988 and at that time included one researcher and one PhD student.

The core thematic of the "high energies" group is the study of multi-wavelength emission and variability of active galactic nuclei, especially in the visible and ultraviolet. Following the launch of INTEGRAL satellite of the European Space Agency (ESA), which aims to observe the hard X-ray and low energy gamma rays, the group has expanded to lead the consortium of data processing, the INTEGRAL Science Data Centre (ISDC). This project has resulted in a significant diversification of scientific topics addressed in the group of high energies. The center of gravity of the study of active galactic nuclei has thus moved to the area covered by INTEGRAL, with particular emphasis on the ability of the satellite to observe heavily obscured sources. Meanwhile, galactic X-ray sources such as X-ray binary low and high masses, transient X-ray sources and super-fast X novas, or collisions wind around massive stars and pulsars, became subjects very important. The largest cosmological scales, INTEGRAL makes a significant contribution to the study of galaxy cluster fusion by measuring the intensity of X-radiation emitted by relativistic electrons, resulting from shocks in the gas in the cluster.

Beyond energy accessible to INTEGRAL, at astroparticle border, the methods of observation at very high and ultra-high energies have recently made considerable progress with FERMI in space and HESS on ground. FERMI allows observation of many jets of active nuclei of blazar type, of pulsar, of gamma-ray bursts and supernovae remnants. The high-energy group is currently involved in these issues, both on the theoretical level of particle acceleration and at the observational level, in particular to prepare for the exploitation of the new generation telescope data observing ultra-high energies, the Cherenkov Telescope Array (CTA), the successor of HESS, which is under development. In parallel, the group is involved in the study of blazars jets by the PLANCK satellite.

The study of particle acceleration combining the new possibilities of observation of high-energy radiation such as HESS and FERMI and theoretical modeling is a new activity at the ISDC. This research focuses on the mechanisms of ultra-relativistic jets emitted by supermassive black holes and gamma-ray bursts as well as the origin of extremely high energy cosmic rays and the origin of magnetic fields at high scale in the Universe.

POLAR is a new activity within the group. It is the development of a polarized X-ray detector, in order to measure the polarization of the emission of high-energy gamma-ray bursts. Discussions are ongoing with the Chinese astronomers to install POLAR on the future Chinese space station.

The continuation of traditional activities of the high-energy group goes through the implementation of new observatory projects in the X-rays. The group is heavily involved in the Japanese ASTRO-H project, it was launched on February 17, 2016, proposing a hardware contribution, a filter wheel for the cryogenic micro- calorimeter instrument, in collaboration with the Department of Nuclear and Particle Physics from the University of Geneva. ASTRO-H renamed HITOMI, will cover the same area  of energy as INTEGRAL with a gain greater than one hundred in sensitivity, and will therefore continue the current main areas of research. Moreover, the cryogenic detector will be the first detector of this kind and will provide unique scientific perspectives, thanks to the simultaneous presence of high spatial and spectral resolutions. Priority targets will be the emission of active galactic nuclei, in particular of the very absorbed objects, and clusters of galaxies.

The observatory of the future in high energy is ATHENA, which could be launched in 2028. As for ASTRO-H/HITOMI, the high-energy group prepares for an active participation in this project by providing the hardware equipment for two of the five instruments that will be installed. ATHENA is a major astrophysics project, to be compared to the James Webb Space Telescope (JWST) or Extremely Large Telescope (E-ELT) in terms of sensitivity. For this reason, his chosen field is high energies cosmology, such as the birth of supermassive black holes, the proto-clusters of galaxies and the intergalactic medium, as well as tests of the gravity in very strong field.