7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Status and Latest Results from LHAASO on ϒ-ray and Cosmic Ray Physics
Siming Liu on behalf of the LHAASO collaboration
School of Physical Science and Technology, Southwest Jiaotong University
e-mail: liusm@swjtu.edu.cn

The LHAASO collaboration has more than 280
members from 32 institutes in 5 countries. The
commission of LHAASO in 2021 opened the epoch ofultra-high-energy (UHE) gamma-ray astronomy andpaved the way to address the origin of cosmic rays up tohundreds of PeV. Located at Daocheng, Sichuan, on theeastern edge of the Tibetan plateau with an elevation of4410 meters above the sea level (Figure 1), LHAASO’s
KM2A and WCDA arrays have achieved a duty cycle
better than 99% and 98%, respectively, and the WFCTA
has collected more than 2100 hours of high-quality data.
With a large FOV and high sensitivity,
LHAASO-KM2A and WCDA have shown theirsuperiority in UHE and very-high-energy (VHE)
gamma-ray sky survey with the release of the first
LHAASO catalog [1]. 90 sources with an extension lessthan 2︒ were detected with a significance greater than5σ(TS>37). Among these sources, 69 were detected byWCDA, 75 by KM2A and 54 by both arrays (Figure 2).
The mean spectral index of KM2A sources is about 3.5
while those for WCDA sources is 2.5. 43 UHE sourceswere detected above 100 TeV with a significance greaterthan 4 σ . There are 82 sources within the Galactic
latitude of 12︒, and 4 high latitude AGNs. 32 of thesesources haven’t been detected previously in the TeV
range (Figure 2). Half of these sources can be associatedwith pulsar wind nebulae or supernova remnants (SNRs),
1 with AGN, 8 have GeV counterparts, 7 have nocounterpart. Diffuse gamma-ray emission from theGalactic plane was also measured from 10 TeV to 1PeV
[2]. The brightest gamma-ray burst 221009A was also
fully covered by LHAASO [3]. Some preliminary resultson cosmic ray spectra, composition, and anisotropy arealso available. These results together will advance ourunderstanding of the origin of cosmic ray significantly.
In particular, more than 7 SNRs have been detectedby LHAASO (Figure 3). There are also a few UHE
sources likely associated with SNRs. The spectra ofsome of these sources extend beyond 100 TeV, implyingthat they are indeed PeVatrons. However, their soft UHE
spectra means that both leptonic and hadronic processes
can account for the observed UHE emission. Detailed
multiwavelength studies are needed to quantify theircontribution to PeV cosmic rays [4]. More exciting
developments can be anticipated in the coming fewyears.

References[1] LHAASO collaboration, The First LHAASO Catalogof Gamma-Ray Sources, arXiv:2305.17030[2] LHAASO collaboration, Measurement ofultra-high-energy diffuse gamma-ray emission of theGalactic plane from 10 TeV to 1 PeV with
LHAASO-KM2A, arXiv:2305.05372[3] LHAASO collaboration, A tera-electronvolt
afterglow from a narrow jet in an extremely bright
gamma-ray burst 221009A, DOI:
10.1126/science.adg9328[4] Liu, S. et al. The origin of galactic cosmic rays,
Reviews of Modern Plasma Physics, Volume 6, Issue 1,article id.19

Figure 1: Bird view of the LHAASO in 2021

Figure 2: The first LHAASO catalogue with 90 sources(right) and 32 new sources (left)

Figure 3: The spectra of 46 SNRs normalized at 1TeV