Recombining plasma in supernova remnants: Discovery and progress in the last decade

Abstract

Presence of recombining (overionized) plasma in several supernova remnants (SNRs), first suggested by ASCA observations, was anchored by the detection of enhanced radiative recombination continua in Suzaku spectra of the SNRs IC 443 and W49B. This discovery was surprising, because X‐ray‐emitting SNRs were thought to have ionizing plasmas in general. Since then, similar spectral features have been detected from more than a dozen SNRs, implying that the recombining plasma is not uncommon for a certain type of SNRs. This paper reviews the observational and theoretical progress achieved in the last decade toward understanding of the origin of the recombining plasmas in SNRs. It is observationally indicated that all the SNRs whose plasma is in overionization are associated with the so‐called mixed‐morphology class, characterized by a centrally peaked X‐ray profile and rim‐brightened radio emission. The latest studies of W49B with NuSTAR and W44 with XMM‐Newton have provided clear evidence that two distinct mechanisms can work for the formation of the recombining plasma, namely adiabatic cooling and thermal conduction, with the dominant channel depending on the evolutionary stage of SNRs.

The Athena space X‐ray observatory and the astrophysics of hot plasma†

“…Their studies in X‐rays convey prime information on the energy output from the supernovae, stellar wind of massive stars, properties of the interstellar medium, or on the activity of the galactic center massive black hole Sgr A* (Decourchelle et al , and references therein). Recent progress in the field in terms of observations and modeling has been presented during this conference by An , Ferrand , Greco ; Matsumara , Yamaguchi , and Zhou .…”

“…Their studies in X-rays convey prime information on the energy output from the supernovae, stellar wind of massive stars, properties of the interstellar medium, or on the activity of the Galactic center massive black hole Sgr A* (Decourchelle et al, 2013, and references therein). Recent progresses in the field in terms of observations and modelling have been presented during this conference by Ferrand (2019); Greco (2019); Matsumara (2019); Yamaguchi (2019); Zhou (2019). This energy and heavy element injection has a considerable impact on the interstellar medium and the overall dynamics of the Galaxy, generating heating, turbulence, heavy element enrichment, particle acceleration and magnetic field amplification at high Mach number shocks.…”

ALMA CO Observations of the Mixed-Morphology Supernova Remnant W49B: Efficient Production of Recombining Plasma and Hadronic Gamma-rays via Shock-Cloud Interactions

“…Moreover, shockpropagation into the clumpy ISM and/or dense circumstellar matter (CSM) have a potential to explain their mixed-morphology and thermal X-ray radiation (e.g., Shimizu et al 2012;Slavin et al 2017;Zhang et al 2019). Therefore, the shock-interacting ISM plays an important role in understanding their morphology, plasma conditions, and cosmic-ray acceleration (see also reviews by Vink 2012;Yamaguchi 2020;Sano & Fukui 2021). To unveil the physical processes and high-energy phenomena in the mixed-morphology SNRs, detailed comparative studies among the radio-line emission, X-rays, and gamma-rays are needed.…”

Discovery of a Wind-Blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma

“…Two primary scenarios are describing the origin of the recombining plasma in SNRs: adiabatic cooling and thermal conduction scenarios (cf. Yamaguchi 2020). For the adiabatic cooling scenario (a.k.a.…”