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 ${\hat{I}}^3$-ray source 1LHAASO J0056+6346u. Analyzing 979 days of LHAASO-WCDA data and 1389 days of LHAASO-KM2A data, we observed a significant excess of ${\hat{I}}^3$-ray events with both WCDA and KM2A. Assuming a point power-law source with a fixed spectral index, the significance maps reveal excesses of $\sim 12.65\ddot{I}ƒ$, $\sim 22.18\ddot{I}ƒ$, and $\sim 10.24\ddot{I}ƒ$ in the energy ranges of 1--25 TeV, 25--100 TeV, 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 $12.65\ddot{I}ƒ$ by WCDA and $25.27\ddot{I}ƒ$ by KM2A. The best-fit positions derived from WCDA and KM2A data are (R.A. = $13.96^{\circ }\pm 0.09^{\circ }$, Decl. = $63.92^{\circ }\pm 0.05^{\circ }$) and (R.A. = $14.00^{\circ }\pm 0.05^{\circ }$, Decl. = $63.79^{\circ }\pm 0.02^{\circ }$), respectively. The angular size ($r_{39}$) of 1LHAASO J0056+6346u is $0.34^{\circ }\pm 0.04^{\circ }$ at 1--25 TeV and $0.24^{\circ }\pm 0.02^{\circ }$ at $>25$ TeV. The differential flux of this UHE ${\hat{I}}^3$-ray source can be described by an exponential cutoff power-law function: $(2.67\pm 0.25)\times 10^{-15}(E/20\text{TeV}{)}^{-1.97\pm 0.10}{e}^{-E/(55.1\pm 7.2)\text{TeV}}{\text{TeV}}^{-1}{\text{cm}}^{-2}{\text{s}}^{-1}$. To explore potential sources of ${\hat{I}}^3$-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 ${\hat{I}}^3$-ray source might be associated with gas content illuminated by a nearby CR accelerator, possibly the SNR candidate G124.0+1.4.

16 pages, 8 figures, Accepted for publication in SCPMA