Particle reacceleration in the Coma cluster: radio properties and hard X‐ray emission

By Gianfranco Brunetti, G. Setti, L. Feretti, G. Giovannini. 2000

374 citations recorded by the source corpus.

The radio spectral index map of the Coma halo shows a progressive steepening of the spectral index with increasing radius. Such a steepening cannot be simply justified by models involving continuous injection of fresh particles in the Coma halo or by models involving diffusion of fresh electrons from the central regions. We propose a two-phase model in which the relativistic electrons injected in the Coma cluster by some processes (starbursts, AGNs, shocks, turbulence) during a first phase in the past are systematically reaccelerated during a second phase for a relatively long time (∼1 Gyr) up to the present time. We show that for reacceleration time-scales of ∼0.1 Gyr this hypothesis can well account for the radio properties of Coma C. For the same range of parameters which explain Coma C we have calculated the expected fluxes from the inverse Compton scattering of the Cosmic Microwave Background (CMB) photons, finding that the hard X-ray tail discovered by BeppoSAX may be accounted for by the stronger reacceleration allowed by the model. The possibility of extending the main model assumptions and findings to the case of the other radio haloes is also discussed, the basic predictions being consistent with the observations.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/2bf20a55742b9664d9f7e893a423d90bde4e7f66

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Citations in the corpus

Science with the Murchison Widefield Array (2012, background): “Possible mechanisms for accelerating the cosmic ray electrons responsible for this emission are turbulent reacceleration following a cluster merger (Brunetti et al. 2001; Petrosian 2001) and hadronic collisions between cosmic-ray and thermal protons (Dennison 1980; Blasi & Colafrancesco 1999).”
Massive and refined - II. The statistical properties of turbulent motions in massive galaxy clusters with high spatial resolution (2010, background): “…the origin of non thermal components to power such large scale radio emission (e.g. Blasi & Colafrancesco 1999; Sarazin 1999; Dolag & Ensslin 2000; Brunetti et al. 2001) Turbulence in the magnetized ICM may power large scale radio emission in galaxy clusters, provided that relativistic electrons…”
SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS (2013, background): “…the particles through the second order Fermi process to sufficiently high energies to explain the observed radio emission (Schlickeiser et al. 1987; Brunetti et al. 2001; Petrosian 2001; Brunetti et al. 2004; Brunetti & Blasi 2005; Brunetti & Lazarian 2007, 2011; Brunetti et al. 2009; Donnert et…”
Simulating cosmic rays in clusters of galaxies – II. A unified scheme for radio haloes and relics with predictions of the γ-ray emission (2007, background): “…within the ICM (Sarazin2002), until they experience continuous in-situ acceleration either via interactions with magneto-hydrodynamic waves, or through turbulent spectra (Jaffe 1977; Schlickeiser et al. 1987; Brunetti et al. 2001; Ohno et al. 2002; Brunetti et al. 2004; Brunetti & Lazarian 2007).”
Cosmic ray transport in galaxy clusters: implications for radio halos, gamma-ray signatures, and cool core heating (2010, methodology): “The curvature in the total spectrum claimed for the Coma cluster radio halo (Brunetti et al. 2001) are not reproduced in current numerical models of the hadronic scenario.”
Bow Shock and Radio Halo in the Merging Cluster A520 (2004, background): “One of the proposed explanations is that the hard X-ray and radio emissions come from different electron populations in regions with different fields (e.g., Rudnick 2000; Petrosian 2001; Brunetti et al. 2001).”
Turbulent gas motions in galaxy cluster simulations: the role of smoothed particle hydrodynamics viscosity (2005, background): “One promising possibility to explain the extended radio emission on Mpc-scales observed in a growing number of galaxy clusters is to attribute it to electron acceleration by cluster turbulence (e.g., Schlickeiser et al. 1987; Brunetti et al. 2001).”
Cluster Mergers and Non-Thermal Phenomena: A Statistical Magneto-Turbulent Model (2004, background): “…microwave background (CMB) C© 2005 RAS Downloaded from https://academic.oup.com/mnras/article-abstract/357/4/1313/1053666 by guest on 28 July 2018 (Fusco-Femiano et al. 1999, 2000; Rephaeli et al. 1999; Völk & Atoyan 1999; Blasi 2001; Brunetti et al. 2001a; Fujita & Sarazin 2001; Petrosian 2001).”
Diffuse Radio Emission from Galaxy Clusters (2019, methodology): “In the re-acceleration model, a population of seed electrons (e.g., Pinzke et al. 2017) is re-accelerated during powerful states of ICM turbulence (Brunetti et al. 2001; Petrosian 2001; Donnert et al. 2013; Donnert & Brunetti 2014), as a consequence of a cluster merger event.”
Cluster Magnetic Fields (2001, methodology): “Brunetti et al. (2001a) present a method for estimating magnetic fields in the Coma cluster radio halo independent of minimum energy assumptions.”
Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration (2007, background): “…1980; Blasi & Colafrancesco 1999), alternatively different forms of in situ–stochastic acceleration and re–acceleration operating for a small fraction of the cluster life may provide a viable source for high energy emitting particles (Schlickeiser et al. 1987; Brunetti et al. 2001; Petrosian 2001).”
Turbulent Motions and Shocks Waves in Galaxy Clusters simulated with AMR (2009, background): “…at some level: this is claimed from several independent theoretical and numerical approaches (e.g. Bryan & Norman 1998; Ricker & Sarazin 2001; Brunetti et al.2001; Inogamov & Sunyaev 2003; Dolag et al.2005; Subramanian et al.2006; Vazza et al.2006; Brunetti & Lazarian 2007; Nagai et al.2007;…”
Revised equipartition and minimum energy formula for magnetic field strength estimates from radio synchrotron observations (2005, background): “…Fermi shock acceleration (Drury 1983; Schlickeiser 2002; Gabici & Blasi 2003) and the acceleration by MHD waves (Schlickeiser & Miller 1998; Brunetti et al. 2001b; Fujita et al. 2003), the energy spectrum of cosmic rays is a power law inmomentum which translates into a power law in…”
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): “…“primary electron” models, where electrons are re–accelerated in–situ, due to the turbulence injected in the cluster volume by massive merger events (e.g. Brunetti et al. 2001; Petrosian 2001; and the review papers by Brunetti 2003; Sarazin 2004; Petrosian & Bykov 2008); (2) “secondary electron…”
Alfvénic reacceleration of relativistic particles in galaxy clusters: MHD waves, leptons and hadrons (2003, background): “…two predictions have been proposed in the literature, based on either choosing more realistic spectra of the radiating particles or introducing a spatial distribution of non-thermal particles and magnetic fields (Goldshmidt & Rephaeli 1993; Brunetti et al. 2001a; Petrosian 2001; Kuo et al. 2003).”
On the Origin of Radio Halos in Galaxy Clusters (2001, background): “The details of this process, however, remain controversial because of the difficulty in directly accelerating the thermal electrons to relativistic energies (e.g., Tribble 1993; Sarazin 2000; Brunetti et al. 2001; Blasi 2001).”