Context. Radio halos are extended and diffuse non-thermal radio sources present at the cluster center, not obviously associated with any individual galaxy. A strong correlation has been found between the cluster X-ray luminosity and the halo radio power. Aims: We observe and analyze the diffuse radio emission present in the complex merging structure Abell 523, classified as a low luminosity X-ray cluster, to discuss its properties in the context of the halo total radio power versus X-ray luminosity correlation. Methods: We reduced VLA archive observations at 1.4 GHz to derive a deep radio image of the diffuse emission, and compared radio, optical, and X-ray data. Results: Low-resolution VLA images detect a giant radio halo associated with a complex merging region. The properties of this new halo agree with those of radio halos in general discussed in the literature, but its radio power is about a factor of ten higher than expected on the basis of the cluster X-ray luminosity. Conclusions: Our study of this giant radio source demonstrates that radio halos can also be present in clusters with a low X-ray luminosity. Only a few similar cases have so far been found. This result suggests that this source represents a new class of objects, that cannot be explained by classical radio halo models. We suggest that the particle reacceleration related to merging processes is very efficient and/or the X-ray luminosity is not a good indicator of the past merging activity of a cluster.

A giant radio halo in the low luminosity X-ray cluster Abell 523

GIOVANNINI, GABRIELE;
2011

Abstract

Context. Radio halos are extended and diffuse non-thermal radio sources present at the cluster center, not obviously associated with any individual galaxy. A strong correlation has been found between the cluster X-ray luminosity and the halo radio power. Aims: We observe and analyze the diffuse radio emission present in the complex merging structure Abell 523, classified as a low luminosity X-ray cluster, to discuss its properties in the context of the halo total radio power versus X-ray luminosity correlation. Methods: We reduced VLA archive observations at 1.4 GHz to derive a deep radio image of the diffuse emission, and compared radio, optical, and X-ray data. Results: Low-resolution VLA images detect a giant radio halo associated with a complex merging region. The properties of this new halo agree with those of radio halos in general discussed in the literature, but its radio power is about a factor of ten higher than expected on the basis of the cluster X-ray luminosity. Conclusions: Our study of this giant radio source demonstrates that radio halos can also be present in clusters with a low X-ray luminosity. Only a few similar cases have so far been found. This result suggests that this source represents a new class of objects, that cannot be explained by classical radio halo models. We suggest that the particle reacceleration related to merging processes is very efficient and/or the X-ray luminosity is not a good indicator of the past merging activity of a cluster.
Giovannini G.; Feretti L.; Girardi M.; Govoni F.; Murgia M.; Vacca V.; Bagchi J.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/104683
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