Observation of the Crab Nebula with LHAASO-KM2A − a performance study *

Abstract

A sub-array of the Large High Altitude Air Shower Observatory (LHAASO), KM2A is mainly designed to observe a large fraction of the northern sky to hunt for γ-ray sources at energies above 10 TeV. Even though the detector construction is still underway, half of the KM2A array has been operating stably since the end of 2019. In this paper, we present the KM2A data analysis pipeline and the first observation of the Crab Nebula, a standard candle in very high energy γ-ray astronomy. We detect γ-ray signals from the Crab Nebula in both energy ranges of 10 100 TeV and 100 TeV with high significance, by analyzing the KM2A data of 136 live days between December 2019 and May 2020. With the observations, we test the detector performance, including angular resolution, pointing accuracy and cosmic-ray background rejection power. The energy spectrum of the Crab Nebula in the energy range 10-250 TeV fits well with a single power-law function dN/dE = (1.13 0.05 0.08 ) 10 (E/20 TeV) cm s TeV . It is consistent with previous measurements by other experiments. This opens a new window of γ-ray astronomy above 0.1 PeV through which new ultrahigh-energy γ-ray phenomena, such as cosmic PeVatrons, might be discovered.

A 3D Likelihood Analysis Tool for LHAASO-KM2A data

“…A 3D Likelihood Analysis Tool for LHAASO-KM2A data Xiaoyuan Huang ulations and the pointing track of the arrays, the 3D likelihood analysis counld fit source models of arbitrary morphology to the sky image, get the energy spectra information and detection significances simultaneously. The analysis with this software could give consistent results with those using traditional method [3].…”

“…Figure 6 shows the spectral energy distribution (SED) and test statistics (TS) map of the Crab Nebula fitted with BinnedAnalysis.py. Compared with the results in [3], the analysis with this software could give consistent results with those using traditional method.…”

“…Figure 1 shows the planed layout and the fiducial area of the current KM2A half-array used in this analysis. The atmosphere shower and detector response have been simlated for KM2A halfarray, and the event reconstrucion including the core, direction and energy reconstruction and the gamma-ray/cosmic-ray discrimination have been implemented on the simulated and experimental data [3]. Similar to the Fermi-LAT and DAMPE gamma-ray analysis [4], we are developing a 3D likelihood analysis software for the KM2A data.…”

TAIGA - an advanced hybrid detector complex for astroparticle physics, cosmic ray physics and gamma-ray astronomy

“…The LHAASO collaboration using the first five months of data from the KM2A half-array, a standard candle at very high energy-Crab Nebula -is observed to investigate the detector performance and corresponding data analysis pipeline for gamma-rays. The statistical significance of the gammaray signal from Crab Nebula is 28.0 ϭ at 25-100 TeV and 14.7 ϭ at >100 TeV [5]. As well, the LHAASO collaboration reported about the detection of more than 530 photons at energies above 100 TeV and up to 1.4 PeV from 12 ultrahigh-energy γ-ray sources with a statistical significance greater than 7 ϭ [6].…”

Muons as a tool for background rejection in imaging atmospheric Cherenkov telescope arrays

“…However, excellent hadron rejection power, that is, over a factor 10 4 reduction, is possible only at tens of TeV. Detector arrays such as LHAASO [3] have demonstrated the power of this approach through the deployment of extensive muon detector arrays, leading to a dramatic reduction in the background above tens and even hundreds of TeVs.…”