📝 SummarXiv

Abstract

We report the detection of high-energy $\gamma$-ray emission in the vicinity of G172.8+1.5, which is debated as a Supernova remnant (SNR) or an ionized hydrogen (H$_{\rm{II}}$) region. Using 16-yr Pass 8 data from Fermi Large Area Telescope (Fermi-LAT), we found the GeV emission can be described by two extended sources with different photon spectra. Among them, the much more extended $\gamma$-ray source SrcA with a Power-law spectrum is spatially coincident with a giant neutral Hydrogen shell structure and several OB stars inside a huge H$_{\rm{II}}$ region. The softer Log-Parabola spectra $\gamma$-ray source SrcB is spatially coincident with a star-forming region with several OB stars, maser sources and IR sources. Gas observation results display a dense molecular cloud surrounding SrcB in the velocity range of [-25,-5] km s$^{-1}$. The possible origins of $\gamma$-ray emission are discussed, including CRs escaped from SNR shock surface and illuminated nearby MC, the young massive star clusters associated with the star-forming region and a pulsar halo generated by an invisible energetic pulsar inside the SNR. Furthermore, under the hadronic scenario, the measured diffusion coefficient in the compact SrcB region is significantly lower than that of the more extended SrcA. This suppression is likely attributed to cosmic-ray-driven instabilities, which reduce the diffusion efficiency in the vicinity of the source relative to the standard conditions in the interstellar medium (ISM). Future advanced analysis from LHAASO observation results would help distinguish the origins of $\gamma$-ray emission in this region and clarify the nature of this source.