Multiwavelength studies of G298.6−-0.0: An old GeV supernova remnant interacting with molecular clouds

Hadronic $\gamma$-ray sources associated with supernova remnants (SNRs) can serve as stopwatches for the escape of cosmic rays from SNRs, which gradually develops from highest-energy particles to lowest-energy particles with time. In this work, we analyze the 13.7~yr \emph{Fermi}-LAT data to investigate the $\gamma$-ray feature in/around the SNR G298.6$-$0.0 region. With $\gamma$-ray spatial analyses, we detect three point-like components. Among them, Src-NE is at the eastern SNR shell, and Src-NW is adjacent to the western edge of this SNR. Src-NE and Src-NW demonstrate spectral breaks at energies around/below 1.8~GeV, suggesting an old SNR age of $>$10~kyr. We also look into the X-ray emission from the G298.6$-$0.0 region, with the Chandra-ACIS data. We detected an extended keV source having a centrally filled structure inside the radio shell. The X-ray spectra are well fit by a model which assumes a collisional ionisation equilibrium of the thermal plasma, further supporting an old SNR age. Based on our analyses of the NANTEN CO- and ATCA-Parkes HI-line data, we determined a kinematic distance of $\sim$10.1~kpc from us to G298.6$-$0.0. This distance entails a large physical radius of the SNR of $\sim$15.5~pc, which is an additional evidence for an old age of $>$10~kyr. Besides, the CO data cube enables us to three-dimensionally locate the molecular clouds (MCs) which are potentially interacting with SNR G298.6$-$0.0 and could account for the hadronic $\gamma$-rays detected at Src-NE or Src-NW. Furthermore, the multiwavelength observational properties unanimously imply that the SNR--MC interaction occurs mainly in the northeast direction.Comment: Accepted by Publications of the Astronomical Society of Japan (PASJ) on 16-Jan-202

A New Gamma-Ray Source in the Vicinity of the Galactic Supernova Remnant G306.3−-0.9

A new extended gamma-ray source, which was named as Source A, in the southwest of Galactic supernova remnant (SNR) G306.3$-$0.9 was detected with a significance of $\sim$13$\sigma$ at the location of R.A. (J2000) = 13$^{\rm{h}}$ 17$^{\rm{m}}$ 52$^{\rm{s}\!\!}$.80, Decl. (J2000) = $-$63$^{\circ}$ 55$'$ 48$"\!\!$.00 using about 9 years of Fermi-LAT data. In order to investigate this unidentified gamma-ray source in multi-wavelengths, we performed Swift observations of Source A. In this presentation we summarize the published gamma-ray results, report about the recent ToO Swift observations of Source A, and show our preliminary results of the gamma-ray analysis that we conducted using the new X-ray data.Comment: Published in proceedings of "7th Fermi Symposium 2017", PoS(IFS2017)10

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

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 $\sim$10 years 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 $\sim$25$\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 $\sim$6$\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.Comment: 12 pages, 7 figures, accepted for publication in MNRA