The structure of cluster merger shocks: turbulent width and the electron heating time-scale

Russell, H. R.; Nulsen, P. E. J.; Caprioli, D.; Chadayammuri, U.; Fabian, A. C.; Kunz, M. W.; McNamara, B. R.; Sanders, J. S.; Richard-Laferrière, A.; Beleznay, M.; Canning, R. E. A.; Hlavacek-Larrondo, J.; King, L .J.

Abstract

We present a new 2 Ms Chandra observation of the cluster merger Abell 2146, which hosts two huge M∼2 shock fronts each ∼500 kpc across. For the first time, we resolve and measure the width of cluster merger shocks. The best-fit width for the bow shock is 17 ± 1 kpc and for the upstream shock is 10.7 ± 0.3 kpc. A narrow collisionless shock will appear broader in projection if its smooth shape is warped by local gas motions. We show that both shock widths are consistent with collisionless shocks blurred by local gas motions of 290 ± 30 km s −1. The upstream shock forms later on in the merger than the bow shock and is therefore expected to be significantly narrower. From the electron temperature profile behind the bow shock, we measure the timescale for the electrons and ions to come back into thermal equilibrium. We rule out rapid thermal equilibration of the electrons with the shock-heated ions at the 6σ level. The observed temperature profile instead favours collisional equilibration. We find no evidence for electron heating over that produced by adiabatic compression. This supports the existing picture from collisionless shocks in the solar wind and supernova remnants. The upstream shock is consistent with this result but has a more complex structure, including a ∼ 2 keV increase in temperature ∼50 kpc ahead of the shock.

Citation

Russell, H. R., Nulsen, P. E. J., Caprioli, D., Chadayammuri, U., Fabian, A. C., Kunz, M. W., McNamara, B. R., Sanders, J. S., Richard-Laferrière, A., Beleznay, M., Canning, R. E. A., Hlavacek-Larrondo, J., & King, L. .. (2022). The structure of cluster merger shocks: turbulent width and the electron heating time-scale. Monthly Notices of the Royal Astronomical Society, 514(1), 1477-1493. https://doi.org/10.1093/mnras/stac1055

• Journal Article Type: Article
• Acceptance Date: Apr 4, 2022
• Online Publication Date: Jun 11, 2022
• Publication Date: Jul 1, 2022
• Deposit Date: Jul 4, 2022
• Publicly Available Date: Jul 4, 2022
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Oxford University Press
• Peer Reviewed: Peer Reviewed
• Volume: 514
• Issue: 1
• Pages: 1477-1493
• DOI: https://doi.org/10.1093/mnras/stac1055
• Public URL: https://nottingham-repository.worktribe.com/output/7755131
• Publisher URL: https://academic.oup.com/mnras/article-abstract/514/1/1477/6587066?redirectedFrom=fulltext&login=false
• Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2022. The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.