Form 8

Research Result Report
ICRR Inter-University Research Program 2022
Research Subject: Study of high-energy cosmic rays at a high altitude in Tibet, China
Principal Investigator: Ding Chen, Professor, National Astronomical Observatories ofChina, CAS, (China)
Participating Researchers:

Summary of Research Result：
1. Tibet AS + MD experiment
The Tibet-AS+MD experiment (Tibet Air shower array + Muon Detector arrayexperiment), which aims to develop gamma-ray astronomy in the 100 TeV region (101000 TeV), has been actively done. In FY2022, we continued to develop a new softwaretool for data analysis. We focused on HESS J1843-033 as a gamma-ray source, which
is a very high-energy gamma-ray source whose origin is still unknown. A gamma-ray
source with an extension of 0°.34 ± 0°.12 was successfully detected above 25 TeV at(α, δ) = (281°.09 ± 0°.10, -3°.76 ± 0°.09) near HESS J1843-33. The statisticalsignificance is 6.2σ and the source is named TASG J1844-038. The position of TASG
J1844-038 is consistent with the positions of HESS J1843-033, eHWC J1842-035 andLHAASO J1843-0338. At 25 TeV < E < 130 TeV the measured gamma-ray energy
spectrum is described by dN/dE = (9.70±1.89) x 10-16 x (E/40 TeV)-(3.26±0.30) TeV-1 cm-2s-1 (Figure 1).Fitting our results with the combined spectra of HESS J1843-033 andLHAASO J1843-0338 suggests the presence of a cutoff at 49.5±9.0 TeV for TASG
J1844-038. The correlation between TASG J1844-038 and nearby SNR G28.6-0.1 andPSR J1844-0346 is discussed in detail for the first time (ApJ, 932:120, pp1-8 (2022)).
Kurashige et al. performed a Monte Carlo simulation assuming the air shower arrayand the underground muon detector to estimate their sensitivity with respect to theenergy spectrum of primary cosmic ray protons in the 40-630 TeV range. The results
show that protons can be selected with 90% purity. The survival ratio of protons
including model dependence is 14.2%-19.1% at about 35 TeV and 3.7%-7.4% at aboutForm 8450 TeV. Systematic errors in the proton flux from hadronic-interaction and cosmicray composition models are estimated to be less than ±37%. With a significantly
larger effective area than satellite experiments as well as high proton selection
capability, the Tibet AS+MD experiment is able to observe the cosmic ray proton
spectrum with high statistical accuracy over the energy range from tens to hundredsof TeV (Figure 2: PTEP 2022:093F01, pp1-15 (2022)).
2. Tibet AS + YAC experiment
The Tibet AS + YAC (Tibet air shower core detector array) experiment, which aims
to observe the energy spectrum of each particle component in the knee region cosmicrays, is being promoted. The Tibet air shower core detector array (YAC-II), whichconsists of 124 air shower core detectors [burst detectors], is installed near the centerof the Tibet Air Shower Observatory. In FY2014, electronics and data acquisition
software were implemented, and YAC-II, which focuses on proton discrimination incosmic rays in the Knee energy region, started data acquisition. In FY2022, softwaretools for analysis were actively developed using Monte Carlo simulations.

Fig.1 Gamma-ray energy spectrum

Fig. 2 Predicted cosmic-ray proton

from TASG J1844-038 observed byenergy spectra obtained from a Montethe Tibet AS+MD experiment (redCarlo simulation of the Tibet AS+MD

circles: This work).

experiment,

assuming

twocosmic-ray

composition

modelsprimary

three hadron interaction models.
3. International Conferences
13 presentations at ISVHECRI2022 and others.
4. Publications[1] M. Amenomori et al., ApJ, 932:120, pp1-8 (2022).
[2] D. Kurashige et al., Prog. Theor. Exp. Phys. 2022:093F01, pp1-15 (2022).
No. F004

and