Population study of Galactic supernova remnants at very high γ-ray energies with H.E.S.S.

Abstract

Shell-type supernova remnants (SNRs) are considered prime candidates for the acceleration of Galactic cosmic rays (CRs) up to the knee of the CR spectrum at E ≈ 3 × 10 15 eV. Our Milky Way galaxy hosts more than 350 SNRs discovered at radio wavelengths and at high energies, of which 220 fall into the H.E.S.S. Galactic Plane Survey (HGPS) region. Of those, only 50 SNRs are coincident with a H.E.S.S source and in 8 cases the very high-energy (VHE) emission is firmly identified as an SNR. The H.E.S.S. GPS provides us with a legacy for SNR population study in VHE γ-rays and we use this rich data set to extract VHE flux upper limits from all undetected SNRs. Overall, the derived flux upper limits are not in contradiction with the canonical CR paradigm. Assuming this paradigm holds true, we can constrain typical ambient density values around shell-type SNRs to n ≤ 7 cm -3 and electron-to-proton energy fractions above 10 TeV to ep ≤ 5 × 10 −3 . Furthermore, comparisons of VHE with radio luminosities in non-interacting SNRs reveal a behaviour that is in agreement with the theory of magnetic field amplification at shell-type SNRs.

The supernova remnant SN 1006 as a Galactic particle accelerator

“…Accelerated protons in SNRs might provide γ − ray emission through interaction with protons in their environment leading to π 0 production and subsequent decay. TeV γ − ray emission from a handful of shell-like SNRs has been observed 6 , while GeV emission has been detected in about 30 remnants 7 . In SN 1006, γ − ray emission has been detected in both the TeV and GeV bands, with the HESS observatory 8 and Fermi telescope 9 , respectively, but its nature is uncertain, since γ − ray emission can also be produced by inverse Compton from ultrarelativistic electrons (leptonic scenario).…”

Survey of the Galactic Plane with the Cherenkov Telescope Array

“…Current gamma-ray observations in the very-high-energy (VHE) domain (above a few tens of GeV) have revealed a wide range of particle acceleration and interaction phenomena in Galactic astrophysical objects including pulsar wind nebulae (PWNe, e.g., [1]), supernova remnants (SNRs, e.g., [2]), and gamma-ray binaries [e.g. 3], as well as many sources whose nature is still unknown.…”

Discovery of the Ultra-High-Energy gamma-ray source LHAASO J2002+3238 spatially associated with SNR G69.7+1.0

“…Other experiments also have observed this region in the gamma range, a job deep observations toward the Cygnus region using 300 hr of very high energy (VHE) 𝛾-ray data taken with the VERITAS Cerenkov telescope array gives a upper limit of this source [14] and H.E.S.S. also give a upper limit to this SNR [15]. In addition, LHAASO-WCDA has also observed phenomena here, but its significance has not yet reached 5 𝜎.…”