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

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

Citation Formats
A. Sezer, T. Ergin, R. Yamazaki, H. Sano, and Y. Fukui, “Discovery of recombining plasma inside the extended gamma-ray supernova remnant HB9,” MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, vol. 489, no. 3, pp. 4300–4310, 2019, Accessed: 00, 2020. [Online]. Available: