Study of ultra-high-energy gamma-ray source 1LHAASO J0056+6346u and its possible origins

Abstract

We report a dedicated study of the newly discovered extended UHE γ-ray source 1LHAASO J0056+6346u. Analyzing 979 d of LHAASO-WCDA data and 1389 d of LHAASO-KM2A data, we observed a significant excess of γ-ray events with both WCDA and KM2A. Assuming a point power-law source with a fixed spectral index, the significance maps reveal excesses of 12.65 σ, 22.18 σ, and 10.24 σ in the energy ranges of 1–25, 25–100, and >100 TeV, respectively. We use a 3D likelihood algorithm to derive the morphological and spectral parameters, and the source is detected with significances of 13.72 σ by WCDA and 25.27 σ by KM2A. The best-fit positions derived from WCDA and KM2A data are (R.A. = 13.96° ± 0.09°, Decl. = 63.92° ± 0.05°) and (R.A. = 14.00° ± 0.05°, Decl. = 63.79° ± 0.02°), respectively. The angular size (r<inf>39</inf>) of 1LHAASO J0056+6346u is 0.34° ± 0.04° at 1–25 TeV and 0.24° ± 0.02° at >25 TeV. The differential flux of this UHE γ-ray source can be described by an exponential cutoff power-law function: (2.67 ± 0.25) × 10⁻¹⁵ (E/20 TeV)^{(−1.97±0.10)} e^{−E/(55.1±7.2) TeV} TeV⁻¹ cm⁻² s⁻¹. To explore potential sources of γ-ray emission, we investigated the gas distribution around 1LHAASO J0056+6346u. 1LHAASO J0056+6346u is likely to be a TeV PWN powered by an unknown pulsar, which would naturally explain both its spatial and spectral properties. Another explanation is that this UHE γ-ray source might be associated with gas content illuminated by a nearby CR accelerator, possibly the SNR candidate G124.0+1.4.