Bow Shock and Radio Halo in the Merging Cluster A520

By M. Markevitch, F. Govoni, G. Brunetti, D. J. CfA, Iki, Moscow, Ist. Radioastron., Bologna. 2004

244 citations recorded by the source corpus.

Chandra observations of the merging galaxy cluster A520 reveal a prominent bow shock with M = 2.1. This is only the second clear example of a substantially supersonic merger shock front in clusters. Comparison of the X-ray image with that of the previously known radio halo reveals a coincidence of the leading edge of the halo with the bow shock, offering an interesting experimental setup for determining the role of shocks in the radio halo generation. The halo in A520 apparently consists of two spatially distinct parts, the main turbulence-driven component and a cap-like forward structure related to the shock, where the latter may provide preenergized electrons for subsequent turbulent reacceleration. The radio edge may be caused by electron acceleration by the shock. If so, the synchrotron spectrum should have a slope of α ≃ 1.2 right behind the edge, with quick steepening farther away from the edge. Alternatively, if shocks are inefficient accelerators, the radio edge may be explained by an increase in the magnetic field and density of preexisting relativistic electrons due to gas compression. In the latter model, there should be radio emission in front of the shock with the same spectrum as that behind it, but 10-20 times fainter. If future sensitive radio measurements do not find such preshock emission, then the electrons are indeed accelerated (or reaccelerated) by the shock, and one will be able to determine its acceleration efficiency. We also propose a method to estimate the magnetic field strength behind the shock, based on measuring the dependence of the radio spectral slope upon the distance from the shock. In addition, the radio edge provides a way to constrain the diffusion speed of the relativistic electrons.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/5dbf90716f5bcc7141e6283289607cd672e8e404

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Citations in the corpus

GMRT radio halo survey in galaxy clusters at z = 0.2–0.4 - II. The eBCS clusters and analysis of the complete sample (2008, background): “…exists between the presence of relics and dynamical activity in the hosting clusters, and all models proposed so far to explain the origin of relics invoke the presence of a merger shock (e.g. Enßlin et al. 1998; Roettiger et al. 1999; Enßlin & Gopal–Krishna 2001; Markevitch et al. 2005).”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “Observationlly, merger shocks have been detected only in a few in a few nearby X-ray bright galaxy clusters (Markevitch et al.2005; Markevitch 2006; Solovyeva et al.2008), and may be possibly associated with single or double radio relics discovered in a number of galaxy clusters (e.g. Roettgering…”
A Dark Core in Abell 520 (2007, methodology): “X-ray data We reanalyze ObsID 4215, the 67ks Chandra X-ray observation originally described by Markevitch et al. (2005), using the CIAO 3.3 reduction software and CALDB version 3.2.0 along with the standard background analysis tools.”
X-ray–optical classification of cluster mergers and the evolution of the cluster merger fraction (2011, background): “Evidence of past and ongoing merging is found in the form of a bow shock (one of less than a handful of supersonic shocks detected so far in cluster mergers) and a complex radio halo (Markevitch et al. 2005).”
The case for electron re-acceleration at galaxy cluster shocks (2017, background): “A solution to explain the apparent very efficient acceleration, is to invoke the presence of a population of fossil relativistic electrons [18], with Lorentz factors γ & 102.”
Subaru Weak Lensing Study of Seven Merging Clusters: Distributions of Mass and Baryons (2007, background): “Markevitch et al. (2005) discovered with Chandra Xray observations a bow-shaped shock close to a dense gas clump in the cluster A520 at z = 0.199.”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, background): “A 520 (Markevitch et al. 2005; Markevitch and Vikhlinin 2007); A2219 (Million and Allen 2008).”
Acceleration of primary and secondary particles in galaxy clusters by compressible MHD turbulence: from radio haloes to gamma-rays (2010, background): “…evidence for the latter process come from the observations of radio relics that indeed suggest a connection between shocks and electron acceleration (or reacceleration) in the IGM (e.g., Markevitch et al 2005 and Giacintucci et al 2008 for observations of a shocks–relics connection in clusters).”
Diffuse Radio Emission from Galaxy Clusters (2019, background): “Therefore, CR electrons might be re-accelerated from this seed population in the ICM (Enßlin et al. 1998; Markevitch et al. 2005; Kang & Ryu 2011; Kang et al. 2012), mitigating some of the DSA requirements (see also Section 6.2).”