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Tamotsu Sato, Katsuji Koyama, Tadayuki Takahashi, Hirokazu Odaka, Shinya Nakashima, Discovery of recombining plasma in the supernova remnant 3C 391, Publications of the Astronomical Society of Japan, Volume 66, Issue 6, December 2014, 124, https://doi.org/10.1093/pasj/psu120
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Abstract
Recent X-ray study of middle-aged supernova remnants (SNRs) reveals strong radiative recombination continua (RRCs) associated with overionized plasmas, which origin still remains uncertain. We report a discovery of an RRC in the middle-aged SNR 3C 391. If the X-ray spectrum is fitted with a two-temperature plasma model in collisional ionization equilibrium (CIE), residuals of a Si xiv Lyα line at 2.006 keV, a S xvi Lyα line at 2.623 keV and the edge of a RRC of Si xiii at 2.666 keV are found. In fact, the X-ray spectrum is well described by the composite model consisting of the CIE plasma and a recombining plasma (RP). The abundance pattern suggests that the RP is due to ejecta from core-collapse supernova of the progenitor mass of about 15 M⊙. There is no significant difference of the recombining parameters between the south-east region and the north-west region surrounded by dense molecular clouds. We also find a hint of a Fe i Kα line at 6.4 keV (2.4 σ detection) from the south-east region of the SNR.