Discovery of Very High Energy Gamma-Ray Emissions from the Low-luminosity AGN NGC 4278 by LHAASO

Z Cao, F Aharonian, Axikegu, YX Bai… - The Astrophysical …, 2024 - iopscience.iop.org
Z Cao, F Aharonian, Axikegu, YX Bai, YW Bao, D Bastieri, XJ Bi, YJ Bi, W Bian, AV Bukevich…
The Astrophysical Journal Letters, 2024iopscience.iop.org
The first source catalog of the Large High Altitude Air Shower Observatory (LHAASO)
reported the detection of a very high energy gamma-ray source, 1LHAASO J1219+ 2915.
This Letter presents a further detailed study of the spectral and temporal behavior of this
pointlike source. The best-fit position of the TeV source (RA= 185.° 05±0.° 04, decl.= 29.°
25±0.° 03) is compatible with NGC 4278 within∼ 0.° 03. Variation analysis shows an
indication of variability on a timescale of a few months in the TeV band, which is consistent …
Abstract
The first source catalog of the Large High Altitude Air Shower Observatory (LHAASO) reported the detection of a very high energy gamma-ray source, 1LHAASO J1219+2915. This Letter presents a further detailed study of the spectral and temporal behavior of this pointlike source. The best-fit position of the TeV source (R.A. = 185.°05 ± 0.°04, decl. = 29.°25 ± 0.°03) is compatible with NGC 4278 within ∼0.°03. Variation analysis shows an indication of variability on a timescale of a few months in the TeV band, which is consistent with low-frequency observations. Based on these observations, we report the detection of TeV γ-ray emissions from this low-luminosity active galactic nucleus. The observation by LHAASO's Water Cherenkov Detector Array during the active period has a significance level of 8.8σ with a best-fit photon spectral index Γ = 2.56 ± 0.14 and a flux f 1–10 TeV = (7.0 ± 1.1sta ± 0.35syst) × 10−13 photons cm−2 s−1, or approximately 5% of the Crab Nebula. The discovery of VHE gamma-ray emission from NGC 4278 indicates that compact, weak radio jets can efficiently accelerate particles and emit TeV photons.
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