Discovering the most elusive radio relic in the sky: diffuse shock acceleration caught in the act?

Monday 6 Dec 2021, 13:50 → 14:10 Europe/Rome

0/0-3 - Sala Rosino (Dipartimento di Fisica e Astronomia - Edificio ex-Rizzato)

Speakers: Giorgia Peluso (Università degli Studi di Padova)

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 (z=0.0838) 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 L1.4GHz=4.1±0.8×1023 W Hz−1 and integrated spectral index α=1.15±0.23. We infer for this radio relic a lower bound on the magnetisation of B≥0.4μG, a shock Mach number of M≈3.79, 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.

2004.10752.pdf

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