Discovery of a new $\gamma$-ray source LHAASO J0341+5258 with emission up to 200TeV

TL;DR

This paper reports the discovery of a new high-energy gamma-ray source in the Galactic plane, LHAASO J0341+5258, emitting up to 200 TeV, with detailed positional, spectral, and flux measurements, and discusses possible origins.

Contribution

First identification of a new extended gamma-ray source with emission up to 200 TeV, including spectral analysis and potential origin scenarios.

Findings

Source detected with 8.2 sigma significance above 25 TeV.

Flux is about 20% of Crab Nebula above 25 TeV.

Spectrum shows steepening with a cutoff near 50 TeV.

Abstract

We report the discovery of a new unidentified extended $\gamma$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A.$=55.34^{\circ}\pm0.11^{\circ}$ and Dec$=52.97^{\circ}\pm0.07^{\circ}$. The angular size of LHAASO J0341+5258 is $0.29^\circ \pm 0.06^\circ_{stat} \pm0.02^\circ_{sys}$. The flux above 25 TeV is about $20\%$ of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index $\alpha=2.98 \pm 0.19_{stat} \pm 0.02_{sys}$ is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %($\alpha \leq 1.75$) spectrum with a cutoff at $\approx 50$ TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production.