tokens: been performed) remain candidate stellar cloaks in the recoil scenario. A2261 has two Chandra exposures of 10 and 25 ks (ObsIDs 550 and 5007, respectively), which do not conclusively reveal any accretion onto an SMBH. The X-ray flux in those data is dominated by 0.5–2 keV emission from hot cluster gas, showing a cooled core (Bauer et al. 2005 ). Above 2 keV, there is some emission, possibly a point source consistent with knot 4, although it is too faint to reliably distinguish it from cluster gas emission. 4.2. Assessment of the Radio Relic in the A2261-BCG Core The age of the relic radio source can potentially be understood as a time marker for an event related to the disturbance of the central SMBH, and thus we are interested in understanding the age and nature of this relic. We limited the timescale of last electron energization in the radio source to . The existence of a relic in this BCG is interesting in itself and has a number of potential origins, as discussed in Section 3.3 . To investigate how atypical A2261-BCG’s radio source properties are among BCGs, we compare it with the sample of Hogan et al. ( 2015 ), who systematically studied the radio properties of a large sample of BCGs (including A2261-BCG). In comparison with that sample, we find that the 1.4 GHz radio luminosity is typical of ∼50% of BCGs. Strikingly, we appear to not detect a distinct core in this object down to a 3 σ limit of at 10 GHz. Although the non-detection of a core component in the Hogan ( 2014 ) sample was relatively common, their typical upper limit on core emission was on average a factor of >1000 less stringent than our limit. Nevertheless, they found that ∼30% of their BCGs had clear spectrally identified radio cores, while 30% consisted of only non-core components (i.e., had upper limits on core emission, as in our case), and 30% were complete radio non-detections; see their Table C.1. The most unusual thing about the radio relic in A2261-BCG is its central position combined with its small size and steep spectral index. We show the spectral index distribution in Figure 9 of 30% of the non-core BCGs in the Hogan sample. There are only a handful of targets in the sample with spectra comparable to or steeper than the central relic in A2261-BCG, and it is likely that given the large selection in Hogan ( 2014 ), there is some contamination from BCG-unrelated cluster relics included in this distribution. The distribution of core-dominated BCGs tend to center on indices closer to . Therefore, it seems that the radio spectrum of A2261-BCG lies at the extremity of implied activity and jet ages for BCGs. Figure 9. Distribution of the spectral index for a subset of the Hogan ( 2014 ) BCG sample. Here we show only the ∼30% of BCGs in that sample that are similar to A2261-BCG, in that only a non-radio-core component has been spectroscopically identified in the BCG. Note that Hogan et al.'s measurement of the A2261-BCG is included in the histogram. Our measurement is
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