Gamma-ray signatures of cosmic ray acceleration, propagation, and confinement in the era of CTA

Abstract

Galactic cosmic rays are commonly believed to be accelerated at supernova remnants via diffusive shock acceleration. Despite the popularity of this idea, a conclusive proof for its validity is still missing. Gamma-ray astronomy provides us with a powerful tool to tackle this problem, because gamma rays are produced during cosmic ray interactions with the ambient gas. The detection of gamma rays from several supernova remnants is encouraging, but still does not constitute a proof of the scenario, the main problem being the difficulty in disentangling the hadronic and leptonic contributions to the emission. Once released by their sources, cosmic rays diffuse in the interstellar medium, and finally escape from the Galaxy. The diffuse gamma-ray emission from the * Principal corresponding author, stefano.gabici@apc.univ-paris7.fr, tel. +33157277024, fax. +33157276071 * * Corresponding author Galactic disk, as well as the gamma-ray emission detected from a few galaxies is largely due to the interactions of cosmic rays in the interstellar medium. On much larger scales, cosmic rays are also expected to permeate the intracluster medium, since they can be confined and accumulated within clusters of galaxies for cosmological times. Thus, the detection of gamma rays from clusters of galaxies, or even upper limits on their emission, will allow us to constrain the cosmic ray output of the sources they contain, such as normal galaxies, AGNs, and cosmological shocks. In this paper, we describe the impact that the Cherenkov Telescope Array, a future ground-based facility for very-high energy gamma-ray astronomy, is expected to have in this field of research.

On the potential of the Cherenkov Telescope Array for the study of cosmic-ray diffusion in molecular clouds

“…We have investigated its capabilities for the study of CR diffusion in molecular clouds, by making a phase space exploration of different cases which could be observable with such facility. This complements the study presented by Acero et al (2013). We have showed theoretical predictions for VHE γ-rays fluxes from an accelerator inside a massive cloud.…”

“…only the CR background is included) that would also be interesting for detection. The feasibility of a detection depends mainly on their mass, distance and most of all extension of the gamma-ray emission, as already discussed in Acero et al (2013). Here we assume that the extension is ∼0.7 of the boundaries listed in Dame et al (1987) together with the mass and distances given in that paper.…”

Status of the Cherenkov Telescope Array project

“…Whereas the northern site will most likely be composed of a few LSTs and 20-30 MSTs, the southern site will count with additional 50-70 SSTs (plus 20-30 SCTs) to respond to particular requirements associated to the Galactic science case, e.g., to extend the energy range of observations above 100 TeV for the study of PeVatrons, as well as to achieve a good angular resolution required for imaging the structure of extended sources (Acero et al 2013).…”

The Cherenkov Telescope Array potential for the study of young supernova remnants

“…A preliminary assessment of the capabilities of CTA to detect and resolve sources with properties similar to currently c-ray detected SNRs has been accomplished earlier [40,1]. However, in these studies the known c-ray SNRs RX J1713.7-3946 and Vela…”