Title: Localized Recombining Plasma in G166.0+4.3: A Supernova Remnant with an Unusual Morphology,
Abstract: We observed the Galactic mixed-morphology supernova remnant G166.0+4.3 with
Suzaku. The X-ray spectrum in the western part of the remnant is well
represented by a one-component ionizing plasma model. The spectrum in the
northeastern region can be explained by two components. One is the Fe-rich
component with the electron temperature $kT_e = 0.87_{-0.03}^{+0.02}$ keV. The
other is the recombining plasma component of lighter elements with $kT_e =
0.46\pm0.03$ keV, the initial temperature $kT_{init} = 3$ keV (fixed) and the
ionization parameter $n_et = (6.1_{-0.4}^{+0.5}) \times 10^{11} \rm cm^{-3} s$.
As the formation process of the recombining plasma, two scenarios, the
rarefaction and thermal conduction, are considered. The former would not be
favored since we found the recombining plasma only in the northeastern region
whereas the latter would explain the origin of the RP. In the latter scenario,
an RP is anticipated in a part of the remnant where blast waves are in contact
with cool dense gas. The emission measure suggests higher ambient gas density
in the northeastern region. The morphology of the radio shell and a GeV
gamma-ray emission also suggest a molecular cloud in the region.