Radio view of the Peanut cluster: merger-induced stripping and a radio halo shortly after pericentric passage

K. Rajpurohit; N. Lyskova; E. Churazov; W. Forman; I. Khabibullin; R. Kraft; L. Di Mascolo; T. Mroczkowski; A. Botteon; C. Jones; E. O'Sullivan; C. Zhang; R. J. van Weeren; I. Zhuravleva; G. Schellenberger; J. M. Vrtilek; L. P. David; R. Sunyaev; M. Devlin; S. Dicker; S. Haridas; J. van Marrewijk; B. S. Mason; E. Moravec; J. Orlowski-Scherer; C. Romero; C. L. Sarazin; J. Sievers

arXiv · 2610.34667

Radio view of the Peanut cluster: merger-induced stripping and a radio halo shortly after pericentric passage

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Abstract

The Peanut galaxy cluster (SRGe CL0238.3+2005) offers a rare opportunity to investigate thermal and nonthermal processes only $\sim0.1$\,Gyr after pericentric passage. We present a multi-frequency radio study of this system at $z=0.42$ using new MeerKAT and uGMRT observations, complemented by Chandra and MUSTANG-2 data. We identify two morphologically and spectrally distinct radio components: a double-lobed source in the northern subcluster and extended diffuse emission across the cluster center. The double-lobed source has a strongly curved, ultra-steep spectrum and is offset by $\sim22$\,kpc from the nearest brightest cluster galaxy. Its spectral curvature and positional offset are consistent with remnant AGN plasma that may have been displaced during the merger or reshaped by a shock. The diffuse emission extends over $\sim1$~Mpc and is classified as an ultra-steep spectrum ($α=-1.77\pm0.11$ between 400\,MHz and 1.28\,GHz) radio halo. Its volume-averaged radio emissivity, $(1.1\pm0.1)\times10^{-41}$ erg s$^{-1}$ cm$^{-3}$ Hz$^{-1}$ at 1.4\,GHz, is an order of magnitude higher than the characteristic value for other halos. The radial profile of the halo is well described by a single exponential fit and its radio emission correlates tightly with the X-ray, with a best-fit slope of $1.11\pm0.05$. Chandra and MUSTANG-2 observations reveal candidate surface brightness discontinuities, with the most prominent inner feature coinciding with a region of flatter spectral index, potentially tracing localized particle (re)-acceleration. The coexistence of an extended ultra-steep spectrum radio halo, high radio emissivity, remnant AGN plasma, and candidate X-ray/SZ discontinuities makes the Peanut cluster an important test case for understanding the evolution of diffuse radio emission and its connection to the dynamical state of the intracluster medium in early-stage mergers.

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K. Rajpurohit, N. Lyskova, E. Churazov, W. Forman, I. Khabibullin, R. Kraft, L. Di Mascolo, T. Mroczkowski, A. Botteon, C. Jones, E. O'Sullivan, C. Zhang, R. J. van Weeren, I. Zhuravleva, G. Schellenberger, J. M. Vrtilek, L. P. David, R. Sunyaev, M. Devlin, S. Dicker, S. Haridas, J. van Marrewijk, B. S. Mason, E. Moravec, J. Orlowski-Scherer, C. Romero, C. L. Sarazin, J. Sievers. 2026-10-26. Radio view of the Peanut cluster: merger-induced stripping and a radio halo shortly after pericentric passage. https://arxiv.org/abs/2610.34667

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