Detailed investigation of the gamma-ray emission in the vicinity of SNR W28 with Fermi-LAT
- Univ. of Tokyo (Japan). Inst. for Cosmic Ray Research
- Ibaraki Univ. (Japan). College of Science
- Univ. of Maryland Baltimore County (UMBC), Baltimore, MD (United States). Center for Space Sciences and Technology (CRESST); NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
- Univ. of Paris Diderot, Saclay (France). Inst. of Research into the Fundamental Laws of the Universe (CEA-IRFU)
- Hiroshima Univ. (Japan). Dept. of Physical Sciences
- Nagoya Univ. (Japan). Dept. of Physics and Astrophysics
- Univ. of Bordeaux (France). Gradignan Bordeaux Center for Nuclear Research
- Inst. of Science in Spain (IEEE-CSIC), Barcelona (Spain)
- Max Planck Inst. for Extraterrestrial Physics, Garching (Germany)
- Inst. of Science in Spain (IEEE-CSIC), Barcelona (Spain); Catalan Institution for Research and Advanced Studies (ICREA), Barcelona (Spain)
- Aoyama Gakuin Univ., Kanagawa (Japan). Dept. of Physics and Mathematics
Here, we present a detailed investigation of the γ-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4–0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ-ray emission spatially coincident with TeV sources HESS J1800–240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2-100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides with radio emission from the western part of W28. All of the GeV γ-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s–1. Under the assumption that the γ-ray emission toward HESS J1800–240A, B, and C comes from π0 decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. Furthermore, we constrain the total energy of the CRs escaping from W28 through the same modeling to be larger than ~2 × 1049 erg. The emission from Source W can also be explained with the same CR escape scenario.
- Research Organization:
- SLAC National Accelerator Lab., Menlo Park, CA (United States)
- Sponsoring Organization:
- USDOE
- Contributing Organization:
- Fermi LAT Collaboration
- Grant/Contract Number:
- AC02-76SF00515
- OSTI ID:
- 1356528
- Journal Information:
- The Astrophysical Journal, Vol. 786, Issue 2; ISSN 0004-637X
- Publisher:
- Institute of Physics (IOP)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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