Discovering the most elusive radio relic in the sky: Diffuse Shock Acceleration caught in the act?

Abstract

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 $L_{1.4\mathrm{GHz}}=4.1\pm 0.8\times 10^{23}$ W Hz${}^{-1}$ and integrated spectral index $\alpha =1.15\pm 0.23$. We infer for this radio relic a lower bound on the magnetisation of $B\ge 0.4\mu$G, a shock Mach number of $\mathcal{M}\approx 3.79$, 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.

arXiv commentLetter, 5 pages, 4 figures, accepted for publication on MNRAS Letters

References in corpus (42)

• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• LOFAR: The LOw-Frequency ARray
• Astrophysics Source Code Library
• WSClean: an implementation of a fast, generic wide-field imager for radio astronomy
• The GMRT 150 MHz All-sky Radio Survey: First Alternative Data Release TGSS ADR1
• Calibration of X-ray absorption in our Galaxy
• The LOFAR Two-metre Sky Survey - I. Survey Description and Preliminary Data Release
• The LOFAR Two-metre Sky Survey - II. First data release
• Magnetic Field in Clusters of Galaxies
• Diffuse Radio Emission from Galaxy Clusters
• Revised equipartition & minimum energy formula for magnetic field strength estimates from radio synchrotron observations
• Particle Acceleration on Megaparsec Scales in a Merging Galaxy Cluster
• A Catalog of Galaxy Clusters Observed by XMM-Newton
• Planck 2015 results. XXVII. The Second Planck Catalogue of Sunyaev-Zeldovich Sources
• Bow shock and radio halo in the merging cluster A520
• LOFAR facet calibration
• Systematic effects in LOFAR data: A unified calibration strategy
• Universal thermodynamic properties of the intracluster medium over two decades in radius in the X-COP sample
• The Case for Electron Re-Acceleration at Galaxy Cluster Shocks
• Giant radio relics in galaxy clusters: reacceleration of fossil relativistic electrons?
• LOFAR/H-ATLAS: A deep low-frequency survey of the Herschel-ATLAS North Galactic Pole field
• Evidence for particle re-acceleration in the radio relic in the galaxy cluster PLCKG287.0 +32.9
• Systematic X-ray Analysis of Radio Relic Clusters with SUZAKU
• Shock acceleration efficiency in radio relics
• Search for gamma-ray emission from the Coma Cluster with six years of Fermi-LAT data
• Diffuse radio emission from clusters in the MareNostrum Universe simulation
• Deep VLA observations of the cluster 1RXS J0603.3+4214 in the frequency range 1-2 GHz
• Constraining the efficiency of cosmic ray acceleration by cluster shocks
• Shocks and cold fronts in merging and massive galaxy clusters: new detections with Chandra
• Wideband VLA Observations of Abell 2256 I: Continuum, Rotation Measure and Spectral Imaging
• VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics
• Optical Substructure and BCG Offsets of Sunyaev-Zel'dovich and X-ray Selected Galaxy Clusters
• Relics in galaxy clusters at high radio frequencies
• Can cluster merger shocks reproduce the luminosity and shape distribution of radio relics?
• Curved Radio Spectra of Weak Cluster Shocks
• Particle re-acceleration and Faraday-complex structures in the RXC J1314.4-2515 galaxy cluster
• KYDISC: Galaxy Morphology, Quenching, and Mergers in the Cluster Environment
• Searching for the 3.5 keV Line in the Stacked Suzaku Observations of Galaxy Clusters
• A joint XMM-NuSTAR observation of the galaxy cluster Abell 523: constraints on Inverse Compton emission
• Physical properties of the X-ray gas as a dynamical diagnosis for galaxy clusters
• Observations of the galaxy cluster CIZA J2242.8+5301 with the Sardinia Radio Telescope
• A Chandra Study of Radial Temperature Profiles of the Intra-Cluster Medium in 50 Galaxy Clusters

Cited by in corpus (23)

• LOFAR observations of galaxy clusters in HETDEX
• The Planck clusters in the LOFAR sky. I. LoTSS-DR2: new detections and sample overview
• Dissecting nonthermal emission in the complex multiple-merger galaxy cluster Abell 2744: Radio and X-ray analysis
• Exploring the spectral properties of radio relics I: Integrated spectral index and Mach number
• Morphology of radio relics I: What causes the substructure of synchrotron emission?
• Radio fossils, relics, and haloes in Abell 3266: cluster archaeology with ASKAP-EMU and the ATCA
• Understanding the radio relic emission in the galaxy cluster MACS J0717.5+3745: spectral analysis
• Radio relics radio emission from multi-shock scenario
• Morphology of radio relics II: Properties of polarised emission
• Spectro-polarimetric observations of the CIZA J2242.8+5301 northern radio relic: no evidence of high-frequency steepening
• Radio relics in PSZ2 G096.88+24.18: A connection with pre-existing plasma
• The unusually weak and exceptionally steep radio relic in Abell 2108
• MeerKAT's View of the Bullet Cluster 1E 0657-55.8
• A MeerKAT-meets-LOFAR study of Abell 1413: a moderately disturbed non-cool-core cluster hosting a $\sim 500$ kpc 'mini'-halo
• The prototypical major cluster merger Abell 754. I. Calibration of MeerKAT data and radio/X-ray spectral mapping of the cluster
• Discovery of a double radio relic in ZwCl1447.2+2619: A rare testbed for shock acceleration models with a peculiar surface brightness ratio
• On the Challenges of Cosmic-Ray Proton Shock Acceleration in the Intracluster Medium
• A new enigmatic radio relic in the low mass cluster Abell 2108
• Unveiling The Origin of Peculiar Diffuse Radio Emission in Abell 1351
• A morphological analysis of the substructures in radio relics
• Filamentary Baryons and Where to Find Them: A forecast of synchrotron radiation from merger and accretion shocks in the local Cosmic Web
• Cosmic-ray electrons and the magnetic field of the North Polar Spur
• CHEX-MATE: New detections and properties of the radio diffuse emission in massive clusters with MeerKAT