... ring

Appendix is only available in electronic form at http://www.edpsciences.org

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... Mpc

We use H₀ = 75 km s^-1 Mpc^-1, which implies a scale of 1.252 kpc/arcsec at the distance of the group, $D_{\rm L} = 122$ Mpc, throughout the paper.

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... image

The F450W filter image was obtained from the HST WFPC2 association archive. The image is based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555.

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... 2-10 keV band

The luminosity depends on the spectral model assumed, see Table 2.

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