First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

R.J. van Weeren, H.J.A. Röttgering, D.A. Rafferty, R. Pizzo, A. Bonafede, M. Brüggen, [Unknown] ............, Marinus Jan Bentum

    Research output: Contribution to journalArticleAcademicpeer-review

    44 Citations (Scopus)

    Abstract

    Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diuse steepspectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR Low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of 蚠2:3 0:4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of 蚠0:81 0:03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the eciency of particle acceleration at the shock substantially changed in the last 0:1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent regio
    Original languageUndefined
    Pages (from-to)1-13
    Number of pages13
    JournalAstronomy & astrophysics
    Volume543
    Issue numberA2256
    DOIs
    Publication statusPublished - Jul 2012

    Keywords

    • EWI-22624
    • IR-82401
    • METIS-293218

    Cite this

    van Weeren, R.J. ; Röttgering, H.J.A. ; Rafferty, D.A. ; Pizzo, R. ; Bonafede, A. ; Brüggen, M. ; ............, [Unknown] ; Bentum, Marinus Jan. / First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256. In: Astronomy & astrophysics. 2012 ; Vol. 543, No. A2256. pp. 1-13.
    @article{37a4df43e7c24c969ada60830d721ba3,
    title = "First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256",
    abstract = "Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diuse steepspectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR Low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of 蚠2:3 0:4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of 蚠0:81 0:03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the eciency of particle acceleration at the shock substantially changed in the last 0:1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent regio",
    keywords = "EWI-22624, IR-82401, METIS-293218",
    author = "{van Weeren}, R.J. and H.J.A. R{\"o}ttgering and D.A. Rafferty and R. Pizzo and A. Bonafede and M. Br{\"u}ggen and [Unknown] ............ and Bentum, {Marinus Jan}",
    note = "eemcs-eprint-22624",
    year = "2012",
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    doi = "10.1051/0004-6361/201219154",
    language = "Undefined",
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    van Weeren, RJ, Röttgering, HJA, Rafferty, DA, Pizzo, R, Bonafede, A, Brüggen, M, ............, U & Bentum, MJ 2012, 'First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256', Astronomy & astrophysics, vol. 543, no. A2256, pp. 1-13. https://doi.org/10.1051/0004-6361/201219154

    First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256. / van Weeren, R.J.; Röttgering, H.J.A.; Rafferty, D.A.; Pizzo, R.; Bonafede, A.; Brüggen, M.; ............, [Unknown]; Bentum, Marinus Jan.

    In: Astronomy & astrophysics, Vol. 543, No. A2256, 07.2012, p. 1-13.

    Research output: Contribution to journalArticleAcademicpeer-review

    TY - JOUR

    T1 - First LOFAR observations at very low frequencies of cluster-scale non-thermal emission: the case of Abell 2256

    AU - van Weeren, R.J.

    AU - Röttgering, H.J.A.

    AU - Rafferty, D.A.

    AU - Pizzo, R.

    AU - Bonafede, A.

    AU - Brüggen, M.

    AU - ............, [Unknown]

    AU - Bentum, Marinus Jan

    N1 - eemcs-eprint-22624

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    N2 - Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diuse steepspectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR Low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of 蚠2:3 0:4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of 蚠0:81 0:03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the eciency of particle acceleration at the shock substantially changed in the last 0:1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent regio

    AB - Abell 2256 is one of the best known examples of a galaxy cluster hosting large-scale diuse radio emission that is unrelated to individual galaxies. It contains both a giant radio halo and a relic, as well as a number of head-tail sources and smaller diuse steepspectrum radio sources. The origin of radio halos and relics is still being debated, but over the last years it has become clear that the presence of these radio sources is closely related to galaxy cluster merger events. Here we present the results from the first LOFAR Low band antenna (LBA) observations of Abell 2256 between 18 and 67 MHz. To our knowledge, the image presented in this paper at 63 MHz is the deepest ever obtained at frequencies below 100 MHz in general. Both the radio halo and the giant relic are detected in the image at 63 MHz, and the diuse radio emission remains visible at frequencies as low as 20 MHz. The observations confirm the presence of a previously claimed ultra-steep spectrum source to the west of the cluster center with a spectral index of 蚠2:3 0:4 between 63 and 153 MHz. The steep spectrum suggests that this source is an old part of a head-tail radio source in the cluster. For the radio relic we find an integrated spectral index of 蚠0:81 0:03, after removing the flux contribution from the other sources. This is relatively flat which could indicate that the eciency of particle acceleration at the shock substantially changed in the last 0:1 Gyr due to an increase of the shock Mach number. In an alternative scenario, particles are re-accelerated by some mechanism in the downstream region of the shock, resulting in the relatively flat integrated radio spectrum. In the radio halo region we find indications of low-frequency spectral steepening which may suggest that relativistic particles are accelerated in a rather inhomogeneous turbulent regio

    KW - EWI-22624

    KW - IR-82401

    KW - METIS-293218

    U2 - 10.1051/0004-6361/201219154

    DO - 10.1051/0004-6361/201219154

    M3 - Article

    VL - 543

    SP - 1

    EP - 13

    JO - Astronomy & astrophysics

    JF - Astronomy & astrophysics

    SN - 0004-6361

    IS - A2256

    ER -