Hideaki

Mixed-morphology supernova remnants (MM-SNRs) have center-filled thermal X-ray emissions in a synchrotron radio shell.
From the X-ray spectra of several MM-SNRs (e.g., W49B: Ozawa et al. 2009; IC 443: Yamaguchi et al. 2009), the Suzaku satellite has recently discovered recombining plasmas (RPs) characterized by a higher ionization temperature ($kT_z$) than an electron temperature ($kT_e$), while most of shell-like SNRs are explained as collisional ionization equilibrium (CIE: $kT_z$ = $kT_e$) or ionizing plasma (IP: $kT_z < kT_e$). The formation process of the RPs have not been understood yet.

G166.0+4.3 is a Galactic SNR whose synchrotron radio emission is extremely asymmetric: A large bipolar structure in southwest (Wing region) with a smaller semicircle shell in northeast (Shell region).
From a previous X-ray observation with XMM-Newton, Bocchino et al. (2009) classified G166.0+4.3 as a MM-SNR and reported that the plasma is explained by a typical IP model.
However, the origin of the unusual structure is still unclear.

We have performed a long-time (totally 230~ks) observation of G166.0+4.3 with the Suzaku satellite in 2014.
From the spectral analysis of the Wing region, we confirmed that the plasma is well represented by an IP model with $kT_e$ of 0.85 keV.
Applying a similar IP model to the Shell region, however, we found excesses at $¥sim$2.0~keV and $¥sim$2.6~keV corresponding to $¥rm{Si_{XIII}}$ Ly$¥alpha$ (2.0 keV) and the edge of a radiative recombining continuum of $¥rm{Si_{XIII}}$ (2.67~keV) + $¥rm{S_{XIV}}$ Ly$¥alpha$ (2.63 keV), respectively.
This fact indicates a sign of an RP in the Shell region of G166.0+4.3.
We explained the spectrum as an RP model whose electron temperature is 0.46~keV which is smaller than that of the IP model in Wing region.
We also found that the Fe-rich ejecta asymmetrically spread over the Wing region.
These results suggest an inhomogeneous ambient medium in the vicinity of G166.0+4.3 which provides a clue to the cause of the unusual morphology.
A supportive evidence is shown by a recent Fermi observation.
Miguel (2013) discovered a GeV gamma-ray emission from the northeast part of this remnant, suggesting an existing of nearby molecular clouds.
We also estimated the total ejecta mass to be larger than 8 solar masses.
Although no candidate for progenitor has been detected around this remnant, a core-collapse SN is preferable as its origin.
In this poster, we will present details of our analysis and discuss a relation between the unusual morphology and the cause of the RPs.