Discovery of recombining plasma inside the extended gamma-ray supernova remnant HB9

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Sezer A., Ergin T., Yamazaki R., Sano H., Fukui Y.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol.489, no.3, pp.4300-4310, 2019 (Peer-Reviewed Journal) identifier identifier

  • Publication Type: Article / Article
  • Volume: 489 Issue: 3
  • Publication Date: 2019
  • Doi Number: 10.1093/mnras/stz2461
  • Journal Indexes: Science Citation Index Expanded, Scopus
  • Page Numbers: pp.4300-4310
  • Keywords: ISM: atoms, ISM: individual objects: (HB9: G160.9+2.6), ISM: molecules, ISM: supernova remnants, gamma-rays: ISM, X-rays: ISM, FORMED DENSE SHELL, MOLECULAR CLOUDS, THERMAL CONDUCTION, MODELING W44, HOT INTERIOR, IC 443, EMISSION, RADIATION, GRADIENT, SPECTRUM


We present the results from the Suzaku X-ray Imaging Spectrometer observation of the mixed-morphology supernova remnant (SNR) HB9 (G160.9+2.6). We discovered recombining plasma (RP) in the western Suzaku observation region and the spectra here are well described by a model having collisional ionization equilibrium (CIE) and RP components. On the other hand, the X-ray spectra from the eastern Suzaku observation region are best reproduced by the CIE and non-equilibrium ionization model. We discuss possible scenarios to explain the origin of the RP emission based on the observational properties and concluded that the rarefaction scenario is a possible explanation for the existence of RP. In addition, the gamma-ray emission morphology and spectrum within the energy range of 0.2-300 GeV are investigated using 10 yr of data from the Fermi Large Area Telescope (LAT). The gamma-ray morphology of HB9 is best described by the spatial template of radio continuum emission. The spectrum is well fit to a log-parabola function and its detection significance was found to be 25 sigma. Moreover, a new gamma-ray point source located just outside the south-east region of the SNR's shell was detected with a significance of 6 sigma. We also investigated the archival HI and CO data and detected an expanding shell structure in the velocity range of -10.5 and +1.8 km s(-1) that is coinciding with a region of gamma-ray enhancement at the southern rim of the HB9 shell.