With the opening of the X–ray and gamma–ray windows in the sixties, extremely energetic and violent phenomena were discovered and subsequently found to be ubiquitous in the Universe. The existence of compact objects, in particular black holes, was unveiled. In addition to their obvious interest as objects predicted by General Relativity, it has also been realized that black holes of all masses have a fundamental role in shaping the observable properties of the Universe.
Observations in the high energy domain are fundamental for understanding how matter is organized and behaves around black holes; unravelling how these extreme objects influence their environments on a very large scale; and finding the still elusive obscured massive objects in the center of galaxies. In addition, polarimetry in the hard X-ray domain is an important and unique new diagnostic tool at energies for which the non-thermal processes dominate. Acceleration phenomena, non-thermal processes, and magnetic field topology of all types of sources can be probed using this new and independent observable.
Other major problems in contemporary astrophysics, such as the understanding of acceleration processes at shocks of all sizes in relation to the origin of cosmic rays, or the definitive characterization of the debated non-thermal X-ray energy content of clusters of galaxies, also require observations at high energies. An observatory-type medium mission operating from 1 to 400 keV with excellent characteristics in terms of imaging, spectroscopy, timing, and polarimetry, such as PHEMTO, can provide direct insights into these major fields of research. Indeed, its three orders of magnitude improvement in sensitivity in the hard X-ray band will be a real breakthrough and enable the observation of a wide diversity of astrophysical sources unreachable before.
The PHEMTO scientific objectives can be summarized in five questions of utmost interest for high-energy astrophysics:
- What is the role of magnetic field in our galaxy?
- How accretion links to ejection in accreting black hole and neutron stars systems?
- How to constrain explosion physics in supernovae and their remnants?
- How is the inner region of obscured AGN structured and what is their demography?
- What is the non-thermal X-ray energy content of clusters of galaxies?