On the Nonthermal Emission and Acceleration of Electrons in Coma and Other Clusters of Galaxies

By V. Petrosian. 2001

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Some clusters of galaxies, in addition to thermal bremsstrahlung (TB), emit detectable diffuse radiation from the intracluster medium (ICM) at radio, EUV, and hard X-ray (HXR) ranges. The radio radiation must be due to synchrotron by relativistic electrons, and the inverse Compton scattering by the cosmic microwave background radiation of the same electrons is the most natural source for the HXR and perhaps the EUV emissions. However, simple estimates give a weaker magnetic field than that suggested by Faraday rotation measurements. Consequently, nonthermal bremsstrahlung (NTB) and TB have also been suggested as sources of these emissions. We show that NTB cannot be the source of the HXRs (except for a short period) and that the difficulty with the low magnetic field in the IC model is alleviated if the effects of observational selection bias, nonisotropic pitch angle distribution, and spectral breaks in the energy distribution of the relativistic electrons are taken into account. From these considerations and the strength of the EUV emission, we derive a spectrum for the radiating electrons and discuss possible acceleration scenarios for its production. We show that continuous and in situ acceleration in the ICM of the background thermal electrons is difficult and requires unreasonably high energy input. Similarly, acceleration of injected relativistic electrons, say, by galaxies, seems unreasonable because it will give rise to a much flatter spectrum of electrons than required, unless a large fraction of energy input is carried away by electrons escaping the ICM, in which case one obtains EUV and HXR emissions extending well beyond the boundaries of the diffuse radio source. A continuous emission by a cooling spectrum resulting from interaction with ICM of electrons accelerated elsewhere also suffers from similar shortcomings. The most likely scenario appears to be an episodic injection acceleration model, whereby one obtains a time-dependent spectrum that for certain phases of its evolution satisfies all the requirements.

Subfields: Electrical and Electronic Engineering, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/2c73e6a034556114102c3db5633503f5ea170e40

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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): “…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 models”, which predict…”
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).”
Alfvénic reacceleration of relativistic particles in galaxy clusters: MHD waves, leptons and hadrons (2003, methodology): “…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).”
Shock waves in Eulerian cosmological simulations: main properties and acceleration of cosmic rays (2008, background): “Large-scale radio emission in the form of giant radio haloes may be powered by particle re-acceleration by magnetohydrodynamics (MHD) turbulence injected in the ICM during energetic merging events (Brunetti et al. 2001, 2004, 2008; Petrosian 2001).”
EGRET Upper Limits on the High-Energy Gamma-Ray Emission of Galaxy Clusters (2003, background): “As pointed out by Petrosian (2001), the non– thermal bremsstrahlung cannot be persistently produced onaccount of the low radiation efficiency of electrons in the 100 keV range.”
Acceleration of primary and secondary particles in galaxy clusters by compressible MHD turbulence: from radio haloes to gamma-rays (2010, background): “…and into the acceleration of particles via shocks and turbulence (e.g. Ensslin et al 1998; Sarazin 1999; Blasi 2001; Brunetti et al. 2001, 2004; Petrosian 2001; Miniati et al. 2001; Fujita et al 2003; Gabici & Blasi 2003; Ryu et al. 2003; Cassano & Brunetti 2005; Hoeft & Bruggen 2007; Brunetti…”
X-ray spectroscopy of galaxy clusters: studying astrophysical processes in the largest celestial laboratories (2009, background): “Petrosian (2001) points out that in order to explain the reported hard X-ray luminosity in theComa cluster (see later) by bremsstrahlung emission, the continuous input of energy into the ICM would increase the ICM temperature to 1010 K in Hubble time.”
SEARCH FOR COSMIC-RAY-INDUCED GAMMA-RAY EMISSION IN GALAXY CLUSTERS (2013, background): “…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 al. 2013).”
Cluster Magnetic Fields (2001, background): “Assuming an energy source is available to maintain the supra-thermal tail, Petrosian (2001) shows that the collisional energy input by the supra-thermal particles would be adequate to evaporate the cluster atmosphere on a timescale of order 108 years.”
Feedback heating by cosmic rays in clusters of galaxies (2007, background): “…observation of diffuse radio synchrotron emission (e.g., radio haloes, mini-haloes and relics) in many massive clusters (e.g. Brunetti et al. 2001; Petrosian 2001; Pfrommer & Enßlin 2004; Feretti 2005); recent Chandra and XMM observations also show evidence for a significant nonthermal particle…”
Stochastic Acceleration by Turbulence (2012, background): “…2005), to giants radio 13This can be ascertained by plugging in for the diffusion coefficients in Equation (8) the expressions in Equation (16). galaxy lobes (Lacombe 1977; Achterberg 1979; Eilek 1979), and to intra cluster medium of clusters of galaxies (Petrosian 2001, Brunetti & Lazarian 2007).”
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.”
Cosmic-Ray Electrons in Groups and Clusters of Galaxies: Primary and Secondary Populations from a Numerical Cosmological Simulation (2001, background): “However, Petrosian (2001) argues that, because of the very low efficiency of nonthermal bremsstrahlung with respect to Coulomb losses, in the above model a large amount of energy would need to be dumped into the ICM, leading to an unacceptably large consequent equilibrium temperature.”
Multi-frequency analysis of neutralino dark matter annihilations in the Coma cluster (2005, background): “…in terms of suprathermal electron bremsstrahlung emission for the HXR emission of Coma (see Ensslin et al. 1999, Kempner & Sarazin 2000, see also Petrosian 2001 for a critical discussion) and in this case the EUV emission should be produced either by a different relativistic electron…”
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).”
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).”
High-Resolution X-Ray Spectroscopic Constraints on Cooling-Flow Models for Clusters of Galaxies (2002, background): “…indices and short particle lifetimes in cluster radio minihalos have been invoked to argue for reacceleration of particles in cooling flows (Gitti, Brunetti, & Setti 2002), in addition to reacceleration processes proposed for more extended radio structures in the ICM (e.g., Petrosian 2001).”