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A low-frequency radio halo associated with a cluster of galaxies

Nature volume 455, pages 944–947 (2008)Cite this article

Abstract

Clusters of galaxies are the largest gravitationally bound objects in the Universe, containing about 1015 solar masses of hot (108 K) gas, galaxies and dark matter in a typical volume of 10 Mpc3. Magnetic fields and relativistic particles are mixed with the gas as revealed by giant ‘radio haloes’, which arise from diffuse, megaparsec-scale synchrotron radiation at cluster centre1,2. Radio haloes require that the emitting electrons are accelerated in situ (by turbulence)3,4,5,6, or are injected (as secondary particles) by proton collisions into the intergalactic medium7,8,9,10. They are found only in a fraction of massive clusters that have complex dynamics11,12,13,14, which suggests a connection between these mechanisms and cluster mergers. Here we report a radio halo at low frequencies associated with the merging cluster Abell 521. This halo has an extremely steep radio spectrum, which implies a high frequency cut-off; this makes the halo difficult to detect with observations at 1.4 GHz (the frequency at which all other known radio haloes have been best studied). The spectrum of the halo is inconsistent with a secondary origin of the relativistic electrons, but instead supports turbulent acceleration, which suggests that many radio haloes in the Universe should emit mainly at low frequencies.

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Figure 1: Radio and X-ray images of Abell 521.
Figure 2: Spectrum of the radio halo.
Figure 3: Limits on the energy density of relativistic protons.

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References

  1. Giovannini, G. & Feretti, L. in Diffuse Radio Sources and Cluster Mergers: Radio Haloes and Relics (eds Feretti, L., Gioia, I. M. & Giovannini, G.) 197–227 (Astrophys. Space Sci. Library 272, Kluwer, 2002)

    Google Scholar 

  2. Ferrari, C., Govoni, F., Schindler, S., Bykov, A. M. & Rephaeli, Y. Observations of extended radio emission in clusters. Space Sci. Rev. 134, 93–118 (2008)

    Article  ADS  Google Scholar 

  3. Jaffe, W. J. Origin and transport of electrons in the halo radio source in the Coma cluster. Astrophys. J. 212, 1–7 (1977)

    Article  ADS  Google Scholar 

  4. Schlickeiser, R., Sievers, A. & Thiemann, H. The diffuse radio emission from the Coma cluster. Astron. Astrophys. 182, 21–35 (1987)

    ADS  CAS  Google Scholar 

  5. Brunetti, G., Setti, G., Feretti, L. & Giovannini, G. Particle reacceleration in the Coma cluster: radio properties and hard X-ray emission. Mon. Not. R. Astron. Soc. 320, 365–378 (2001)

    Article  ADS  Google Scholar 

  6. Petrosian, V. On the nonthermal emission and acceleration of electrons in coma and other clusters of galaxies. Astrophys. J. 557, 560–572 (2001)

    Article  ADS  Google Scholar 

  7. Dennison, B. Formation of radio halos in clusters of galaxies from cosmic-ray protons. Astrophys. J. 239, L93–L96 (1980)

    Article  ADS  CAS  Google Scholar 

  8. Blasi, P. & Colafrancesco, S. Cosmic rays, radio halos and nonthermal X-ray emission in clusters of galaxies. Astropart. Phys. 12, 169–183 (1999)

    Article  ADS  Google Scholar 

  9. Dolag, K. & Ensslin, T. A. Radio halos of galaxy clusters from hadronic secondary electron injection in realistic magnetic field configurations. Astron. Astrophys. 362, 151–157 (2000)

    ADS  CAS  Google Scholar 

  10. Pfrommer, C. & Ensslin, T. A. Estimating galaxy cluster magnetic fields by the classical and hadronic minimum energy criterion. Mon. Not. R. Astron. Soc. 352, 76–90 (2004)

    Article  ADS  CAS  Google Scholar 

  11. Giovannini, G., Tordi, M. & Feretti, L. Radio halo and relic candidates from the NRAO VLA Sky Survey. New Astron. 4, 141–155 (1999)

    Article  ADS  Google Scholar 

  12. Buote, D. A. On the origin of radio halos in galaxy clusters. Astrophys. J. 553, L15–L18 (2001)

    Article  ADS  Google Scholar 

  13. Cassano, R. et al. Revised statistics of radio halos and the reacceleration model. Astron. Astrophys. 480, 687–697 (2008)

    Article  ADS  CAS  Google Scholar 

  14. Venturi, T. et al. GMRT Radio Halo Survey in galaxy clusters at z = 0.2 - 0.4. II.The eBCS clusters and analysis of the complete sample. Astron. Astrophys. 484, 327–340 (2008)

    Article  ADS  CAS  Google Scholar 

  15. Fujita, Y., Takizawa, M. & Sarazin, C. L. Nonthermal emissions from particles accelerated by turbulence in clusters of galaxies. Astrophys. J. 584, 190–202 (2003)

    Article  ADS  Google Scholar 

  16. Kuo, P.-H., Hwang, C.-Y. & Ip, W.-H. Diagnostic signatures of radio and hard X-ray emission on particle acceleration processes in the Coma cluster. Astrophys. J. 594, 732–740 (2003)

    Article  ADS  Google Scholar 

  17. Brunetti, G., Blasi, P., Cassano, R. & Gabici, S. Alfvenic reacceleration of relativistic particles in galaxy clusters: MHD waves, leptons and hadrons. Mon. Not. R. Astron. Soc. 350, 1174–1194 (2004)

    Article  ADS  CAS  Google Scholar 

  18. Melrose, D. B. Plasma Astrophysics (Gordon & Breach, 1980)

    Google Scholar 

  19. Cassano, R. & Brunetti, G. Cluster mergers and non-thermal phenomena: a statistical magnetoturbulent model. Mon. Not. R. Astron. Soc. 357, 1313–1329 (2005)

    Article  ADS  CAS  Google Scholar 

  20. Brunetti, G. & Lazarian, A. Compressible turbulence in galaxy clusters: physics and stochastic particle re-acceleration. Mon. Not. R. Astron. Soc. 378, 245–275 (2007)

    Article  ADS  CAS  Google Scholar 

  21. Brunetti, G. et al. Cosmic rays and radio halos in galaxy clusters: New constraints from radio observations. Astrophys. J. 670, L5–L8 (2007)

    Article  ADS  CAS  Google Scholar 

  22. Arnaud, M., Maurogordato, S., Slezak, E. & Rho, J. A521: A cluster forming at the crossing of two filaments? Astron. Astrophys. 355, 461–478 (2000)

    ADS  CAS  Google Scholar 

  23. Ferrari, C., Arnaud, M., Ettori, S., Maurogordato, S. & Rho, J. Chandra observation of the multiple merger cluster Abell 521. Astron. Astrophys. 446, 417–428 (2006)

    Article  ADS  CAS  Google Scholar 

  24. Giacintucci, S. et al. Shock acceleration as origin of the radio relic in A521? Astron. Astrophys. 486, 347–358 (2008)

    Article  ADS  CAS  Google Scholar 

  25. Cohen, A. S. et al. The VLA Low-Frequency Sky Survey. Astron. J. 134, 1245–1262 (2007)

    Article  ADS  Google Scholar 

  26. Sarazin, C. L. The energy spectrum of primary cosmic-ray electrons in clusters of galaxies and inverse Compton emission. Astrophys. J. 520, 529–547 (1999)

    Article  ADS  CAS  Google Scholar 

  27. Brunetti, G. & Blasi, P. Alfvenic reacceleration of relativistic particles in galaxy clusters in the presence of secondary electrons and positrons. Mon. Not. R. Astron. Soc. 363, 1173–1187 (2005)

    Article  ADS  CAS  Google Scholar 

  28. Reimer, O., Pohl, M., Sreekumar, P. & Mattox, J. R. EGRET upper limits on the high-energy gamma-ray emission of galaxy clusters. Astrophys. J. 588, 155–164 (2003)

    Article  ADS  Google Scholar 

  29. Pfrommer, C. & Ensslin, T. A. Constraining the population of cosmic ray protons in cooling flow clusters with γ-ray and radio observations: Are radio mini-halos of hadronic origin? Astron. Astrophys. 413, 17–36 (2004)

    Article  ADS  CAS  Google Scholar 

  30. Cassano, R., Brunetti, G. & Setti, G. Statistics of giant radio haloes from electron reacceleration models. Mon. Not. R. Astron. Soc. 369, 1577–1595 (2006)

    Article  ADS  CAS  Google Scholar 

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Acknowledgements

We acknowledge partial support from ASI-INAF I/088/06/0 and PRIN-INAF 2007. G.B. and R.C. acknowledge the Harvard-Smithsonian Center for Astrophysics, the US Naval Research Laboratory and the National Radio Astronomy Observatory for hospitality and partial support during the preparation of the manuscript. Basic research in radio astronomy at the Naval Research Laboratory is supported by 6.1 base funding. The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. We thank R. Athreya and the staff of the GMRT for their helping during the observations. The GMRT is run by the National Centre for Radio Astrophysics, Tata Institute of Fundamental Research.

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Authors and Affiliations

  1. INAF - Istituto di Radioastronomia, Via P. Gobetti 101, I-40129 Bologna, Italy ,

    G. Brunetti, S. Giacintucci, R. Cassano, T. Venturi & G. Setti

  2. Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts 02138, USA ,

    S. Giacintucci & M. Markevitch

  3. Naval Research Laboratory, Code 7213, Washington DC 20375-5320, USA ,

    W. Lane & N. E. Kassim

  4. Dipartimento di Astronomia, Università di Bologna, Via Ranzani 1, I-40127 Bologna, Italy,

    D. Dallacasa & G. Setti

  5. National Radio Astronomy Observatory, Charlottesville, Virginia 22903-2475, USA ,

    W. D. Cotton

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  1. G. Brunetti
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  2. S. Giacintucci
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Correspondence to G. Brunetti.

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Brunetti, G., Giacintucci, S., Cassano, R. et al. A low-frequency radio halo associated with a cluster of galaxies. Nature 455, 944–947 (2008). https://doi.org/10.1038/nature07379

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