天の川銀河の中心から過去最高エネルギーのガンマ線が観測される(Highest-energy ever gamma rays observed from Milky Way center)

2024-10-22 ロスアラモス国立研究所(LANL)

＜関連情報＞

• https://discover.lanl.gov/news/1022-hawc-gamma-rays/
• https://iopscience.iop.org/article/10.3847/2041-8213/ad772e

HAWCによる100 TeVを超える銀河中心PeVatronの観測 Observation of the Galactic Center PeVatron beyond 100 TeV with HAWC

A. Albert, R. Alfaro, C. Alvarez, A. Andrés, J. C. Arteaga-Velázquez, D. Avila Rojas, H. A. Ayala Solares, R. Babu, E. Belmont-Moreno, A. Bernal
The Astrophysical Journal Letters  Published: 2024 September 20
DOI:10.3847/2041-8213/ad772e

Abstract

We report an observation of ultrahigh-energy (UHE) gamma rays from the Galactic center (GC) region, using 7 yr of data collected by the High-Altitude Water Cherenkov (HAWC) Observatory. The HAWC data are best described as a point-like source (HAWC J1746-2856) with a power-law spectrum (dN/dE=ϕ(E/26TeV)γ), where γ = −2.88 ± 0.15_stat − 0.1_sys and ϕ = 1.5 × 10⁻¹⁵ (TeV cm² s)⁻¹±0.3_stat^+0.08sys _{−0.13 sys} extending from 6 to 114 TeV. We find no evidence of a spectral cutoff up to 100 TeV using HAWC data. Two known point-like gamma-ray sources are spatially coincident with the HAWC gamma-ray excess: Sgr A* (HESS J1745-290) and the Arc (HESS J1746-285). We subtract the known flux contribution of these point sources from the measured flux of HAWC J1746-2856 to exclude their contamination and show that the excess observed by HAWC remains significant (>5σ), with the spectrum extending to >100 TeV. Our result supports that these detected UHE gamma rays can originate via hadronic interaction of PeV cosmic-ray protons with the dense ambient gas and confirms the presence of a proton PeVatron at the GC.