Diagnostic Signatures of Radio and Hard X‐Ray Emission on Particle Acceleration Processes in the Coma Cluster

Kuo, P. H.; Hwang, Chorng-Yuan; Ip, W.-H.

doi:10.1086/376966

Cited by 26 publications

(25 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is a consequence of the assumption of an extended, diffuse HXR emission originating from ICS of CMB photons off relativistic electrons. We note here that the different spatial location of the radio-halo emission and of the bulk of the HXR emission is also a prediction of various models invoked to reproduce the formation of the Coma radio-halo (see, e.g., Brunetti et al 2001;Kuo et al 2003). …”

Section: Discussionsupporting

confidence: 65%

Where does the hard X-ray diffuse emission in clusters of galaxies come from?

Colafrancesco¹,

Marchegiani

Perola

2005

A&A

View full text Add to dashboard Cite

The surface brightness produced by synchrotron radiation in clusters of galaxies with a radio-halo sets a degenerate constraint on the magnetic field strength, the relativistic electron density and their spatial distributions, B(r) and n rel (r), in the intracluster medium. Using the radio-halo in the Coma Cluster as a case study, with the radio brightness profile and the spectral index as the only constraints, predictions are made for the brightness profiles expected in the 20-80 keV band due to Inverse Compton Scattering (ICS) by the relativistic electrons on the Cosmic Microwave Background. This is done for a range of central values of the magnetic field, B, and models of its radial dependence, B(r) (of which two represent extreme situations, namely a constant value either of B or of n rel (r), the third a more realistic intermediate case). It is shown that the possible presence of scalar fluctuations on small scales in the strength of B tends to systematically depress the electron density required by the radio data, hence to decrease the ICS brightness expected. These predictions should be useful to evaluate the sensitivity required in future imaging HXR instruments, in order to obtain direct information on the spatial distribution and content of relativistic electrons, hence on the magnetic field properties. If compared with the flux in the HXR tail, whose detection has been claimed in the Coma cluster (Fusco-Femiano et al. 2004, ApJ, 602, L73), when interpreted as ICS from within the radius R h of the radio-halo, as measured so far, the predictions lead to central values B 0 that are significantly lower than those which have been obtained (albeit still controversial) from Faraday Rotation measurements. The discrepancy is somewhat reduced if the radio-halo profile is hypothetically extrapolated out to R vir , that is about three times R h , or, as suggested by hydrodynamical simulations (Dolag et al. 2002, A&A, 387, 383), if it is assumed that B(r) ∝ n th (r). In the latter case n rel (r) has its minimum value at the center of the cluster. If real and from ICS, the bulk of the HXR tail should then be contributed by electrons other than those responsible for the bulk of the radio-halo emission. This case illustrates the need for spatially resolved spectroscopy in the HXR, in order to obtain solid information on the non-thermal content of clusters of galaxies.

show abstract

Section: Discussionsupporting

confidence: 65%

Where does the hard X-ray diffuse emission in clusters of galaxies come from?

Colafrancesco¹,

Marchegiani

Perola

2005

A&A

View full text Add to dashboard Cite

show abstract

“…This indicates that there should be further processes involved or additional conditions to fulfill to produce radio emission. It is worth to notice that recent models, based on turbulent acceleration, seem to overcome this problem (see Kuo, Hwang & Ip 2003;Brunetti & Blasi 2005;Cassano & Brunetti 2005 and references therein). Note that Cassano & Brunetti (2005) predicted the probability for a galaxy cluster to show giant radio halo to be an increasing function of cluster mass and reproduced the observed fraction of ≈ 30% for massive galaxy clusters.…”

Section: Conclusive Remarksmentioning

confidence: 99%

Simulating large‐scale structure formation with magnetic fields

Dolag¹

2006

Astron Nachr

View full text Add to dashboard Cite

Abstract. In the past, different works based on numerical simulations have been presented to explain magnetic fields (MFs) in the large scale structure and within galaxy clusters. In this review, I will summarize the main findings obtained by different authors and -even if many details are still unclear -I will try to construct a consistent picture of our interpretation of largescale magnetic fields based on numerical effort. I will also sketch how this is related to our understanding of radio emission and summarize some arguments where our theoretical understanding has to be improved to match the observations.

show abstract

“…We finally remark that the hypothesis of constant reacceleration efficiency in the cluster volume may not be valid, according to the following arguments; i) first results from numerical simulations (Norman & Bryan 1999) indicate that the injection of turbulence in clusters is not homogeneous and occurs on very different scales in different regions; ii) detailed calculations of particle acceleration due to Alfvèn waves show that, under reasonable assumptions, the acceleration efficiency slightly increases with distance from the cluster center ; iii) the radiative losses of electrons in the innermost cluster regions may be strongly increased if the magnetic field is larger than the equipartition value, in particular if it is of the order of B IC (e.g. Kuo et al 2003).…”

Section: Implications On Particle Acceleration and Cluster Magnetic Fmentioning

confidence: 99%

Spectral index maps of the radio halos in Abell 665 and Abell 2163

Feretti¹,

Orrù²,

Brunetti³

et al. 2004

A&A

View full text Add to dashboard Cite

Abstract. New radio data at 330 MHz are presented for the rich clusters Abell 665 and Abell 2163, whose radio emission is characterized by the presence of a radio halo. These images allowed us to derive the spectral properties of the two clusters under study. The integrated spectra of these halos between 0.3 GHz and 1.4 GHz are moderately steep: α 0.3 = 1.18, for A665 and A2163, respectively. The spectral index maps, produced with an angular resolution of the order of ∼1 , show features of the spectral index (flattening and patches), which are indication of a complex shape of the radiating electron spectrum, and are therefore in support of electron reacceleration models. Regions of flatter spectrum are found to be related to the recent merger activity in these clusters. This is the first strong confirmation that the cluster merger supplies energy to the radio halo. In the undisturbed cluster regions, the spectrum steepens with the distance from the cluster center. This is interpreted as the result of the combination of the magnetic field profile with the spatial distribution of the reacceleration efficiency, thus allowing us to set constraints on the radial profile of the cluster magnetic field.

show abstract

Diagnostic Signatures of Radio and Hard X‐Ray Emission on Particle Acceleration Processes in the Coma Cluster

Cited by 26 publications

References 39 publications

Where does the hard X-ray diffuse emission in clusters of galaxies come from?

Where does the hard X-ray diffuse emission in clusters of galaxies come from?

Simulating large‐scale structure formation with magnetic fields

Spectral index maps of the radio halos in Abell 665 and Abell 2163

Contact Info

Product

Resources

About