Evidence for Rapid Adiabatic Cooling as an Origin of the Recombining Plasma in the Supernova Remnant W49B Revealed by NuSTAR Observations. (arXiv:1811.04426v1 [astro-ph.HE])

Evidence for Rapid Adiabatic Cooling as an Origin of the Recombining Plasma in the Supernova Remnant W49B Revealed by NuSTAR Observations. (arXiv:1811.04426v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Yamaguchi_H/0/1/0/all/0/1">Hiroya Yamaguchi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tanaka_T/0/1/0/all/0/1">Takaaki Tanaka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wik_D/0/1/0/all/0/1">Daniel R. Wik</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rho_J/0/1/0/all/0/1">Jeonghee Rho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bamba_A/0/1/0/all/0/1">Aya Bamba</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Castro_D/0/1/0/all/0/1">Daniel Castro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Randall K. Smith</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Foster_A/0/1/0/all/0/1">Adam R. Foster</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Uchida_H/0/1/0/all/0/1">Hiroyuki Uchida</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Petre_R/0/1/0/all/0/1">Robert Petre</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Williams_B/0/1/0/all/0/1">Brian J. Williams</a>

X-ray observations of supernova remnants (SNRs) in the last decade have shown
that the presence of recombining plasmas is somewhat common in a certain type
of objects. The SNR W49B is the youngest, hottest, and most highly ionized
among such objects and hence provides crucial information about how the
recombination phase is reached during the early evolutionary phase of SNRs. In
particular, spectral properties of radiative recombination continuum (RRC) from
Fe are the key for constraining the detailed plasma conditions. Here we present
imaging and spectral studies of W49B with NuSTAR, utilizing the highest-ever
sensitivity to the Fe RRC at > 8.8keV. We confirm that the Fe RRC is the most
prominent at the western part of the SNR because of the lowest electron
temperature (~ 1.2 keV) achieved there. Our spatially-resolved spectral
analysis reveals a positive correlation between the electron temperature and
the recombination timescale with a uniform initial temperature of ~ 4 keV,
which is consistent with the rapid adiabatic cooling scenario as an origin of
the overionization. This work demonstrates NuSTAR’s suitability for studies of
thermal emission, in addition to hard nonthermal X-rays, from young and
middle-aged SNRs.

X-ray observations of supernova remnants (SNRs) in the last decade have shown
that the presence of recombining plasmas is somewhat common in a certain type
of objects. The SNR W49B is the youngest, hottest, and most highly ionized
among such objects and hence provides crucial information about how the
recombination phase is reached during the early evolutionary phase of SNRs. In
particular, spectral properties of radiative recombination continuum (RRC) from
Fe are the key for constraining the detailed plasma conditions. Here we present
imaging and spectral studies of W49B with NuSTAR, utilizing the highest-ever
sensitivity to the Fe RRC at > 8.8keV. We confirm that the Fe RRC is the most
prominent at the western part of the SNR because of the lowest electron
temperature (~ 1.2 keV) achieved there. Our spatially-resolved spectral
analysis reveals a positive correlation between the electron temperature and
the recombination timescale with a uniform initial temperature of ~ 4 keV,
which is consistent with the rapid adiabatic cooling scenario as an origin of
the overionization. This work demonstrates NuSTAR’s suitability for studies of
thermal emission, in addition to hard nonthermal X-rays, from young and
middle-aged SNRs.

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