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    Radio observations of the double-relic galaxy cluster Abell 1240

    74503.pdf (3.148Mb)
    Access Status
    Open access
    Authors
    Hoang, D.
    Shimwell, T.
    van Weeren, R.
    Intema, Hubertus
    Rottgering, H.
    Andrade-Santos, F.
    Akamatsu, H.
    Bonafede, A.
    Brunetti, G.
    Dawson, W.
    Golovich, N.
    Best, P.
    Botteon, A.
    Brueggen, M.
    Cassano, R.
    de Gasperin, F.
    Hoeft, M.
    Stroe, A.
    White, G.
    Date
    2018
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Hoang, D. and Shimwell, T. and van Weeren, R. and Intema, H. and Rottgering, H. and Andrade-Santos, F. and Akamatsu, H. et al. 2018. Radio observations of the double-relic galaxy cluster Abell 1240. Monthly Notices of the Royal Astronomical Society. 478 (2): pp. 2218-2233.
    Source Title
    Monthly Notices of the Royal Astronomical Society
    DOI
    10.1093/mnras/sty1123
    ISSN
    0035-8711
    Remarks

    This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

    URI
    http://hdl.handle.net/20.500.11937/74218
    Collection
    • Curtin Research Publications
    Abstract

    We present LOw Frequency Array 120–168 MHz images of the merging galaxy cluster Abell 1240 that hosts double radio relics. In combination with the Giant Metrewave Radio Telescope 595–629 MHz and Very Large Array 2–4 GHz data, we characterized the spectral and polarimetric properties of the radio emission. The spectral indices for the relics steepen from their outer edges towards the cluster centre and the electric field vectors are approximately perpendicular to the major axes of the relics. The results are consistent with the picture that these relics trace large-scale shocks propagating outwards during the merger. Assuming diffusive shock acceleration, we obtain shock Mach numbers of M=2.4 and 2.3 for the northern and southern shocks, respectively. For M≲3 shocks, a pre-existing population of mildly relativistic electrons is required to explain the brightness of the relics due to the high (>10 per cent) particle acceleration efficiency required. However, for M≳4 shocks the required efficiency is ≳1 per cent and ≳0.5 per cent, respectively, which is low enough for shock acceleration directly from the thermal pool. We used the fractional polarization to constrain the viewing angle to ≥53 ± 3° and ≥39 ± 5° for the northern and southern shocks, respectively. We found no evidence for diffuse emission in the cluster central region. If the halo spans the entire region between the relics (∼1.8 Mpc) our upper limit on the power is P1.4 GHz=(1.4±0.6)×1023W Hz−1 which is approximately equal to the anticipated flux from a cluster of this mass. However, if the halo is smaller than this, our constraints on the power imply that the halo is underluminous.

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