TY - JOUR
T1 - The structure of cluster merger shocks
T2 - turbulent width and the electron heating time-scale
AU - Russell, H. R.
AU - Nulsen, P. E.J.
AU - Caprioli, D.
AU - Chadayammuri, U.
AU - Fabian, A. C.
AU - Kunz, M. W.
AU - McNamara, B. R.
AU - Sanders, J. S.
AU - Richard-Laferrière, A.
AU - Beleznay, M.
AU - Canning, R. E.A.
AU - Hlavacek-Larrondo, J.
AU - King, L. J.
N1 - Publisher Copyright:
© 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
PY - 2022/7/1
Y1 - 2022/7/1
N2 - We present a new 2 MsChandra 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-fitting 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 time-scale 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. For these cluster merger shocks, which have low sonic Mach numbers and propagate through a high β plasma, we find no evidence for electron heating over that produced by adiabatic compression. Our findings are expected to be valid for collisionless shocks with similar parameters in other environments and support the existing picture from 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.
AB - We present a new 2 MsChandra 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-fitting 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 time-scale 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. For these cluster merger shocks, which have low sonic Mach numbers and propagate through a high β plasma, we find no evidence for electron heating over that produced by adiabatic compression. Our findings are expected to be valid for collisionless shocks with similar parameters in other environments and support the existing picture from 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.
KW - X-rays: galaxies: clusters
KW - galaxies: clusters: individual: Abell 2146
KW - intergalactic medium
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U2 - 10.1093/mnras/stac1055
DO - 10.1093/mnras/stac1055
M3 - Article
AN - SCOPUS:85133533779
SN - 0035-8711
VL - 514
SP - 1477
EP - 1493
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 1
ER -