1 research outputs found
Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?
The origin of radio relics is usually explained via diffusive shock
acceleration (DSA) or re-acceleration of electrons at/from merger shocks in
galaxy clusters. The case of acceleration is challenged by the low predicted
efficiency of low-Mach number merger shocks, unable to explain the power
observed in most radio relics. In this Letter we present the discovery of a new
giant radio relic around the galaxy cluster Abell 2249 () using
LOFAR. It is special since it has the lowest surface brightness of all known
radio relics. We study its radio and X-ray properties combinig LOFAR data with
uGMRT, JVLA and XMM. This object has a total power of W Hz and integrated spectral index . We infer for this radio relic a lower bound on the magnetisation of
G, a shock Mach number of , and a low
acceleration efficiency consistent with DSA. This result suggests that a
missing population of relics may become visible thanks to the unprecedented
sensitivity of the new generation of radio telescopes.Comment: Letter, 5 pages, 4 figures, accepted for publication on MNRAS Letter