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Observation of the $γ$-ray Emission from W43 with LHAASO

Zhen Cao, F. Aharonian, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, W. Bian, J. Blunier, A. V. Bukevich, C. M. Cai, Y. Y. Cai, W. Y. Cao, Zhe Cao, J. Chang, J. F. Chang, E. S. Chen, G. H. Chen, H. K. Chen, L. F. Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. Chen, S. H. Chen, S. Z. Chen, T. L. Chen, X. B. Chen, X. J. Chen, X. P. Chen, Y. Chen, N. Cheng, Q. Y. Cheng, Y. D. Cheng, M. Y. Cui, S. W. Cui, X. H. Cui, Y. D. Cui, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, Y. X. Diao, A. J. Dong, X. Q. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, J. Fang, J. H. Fang, K. Fang, C. F. Feng, H. Feng, L. Feng, S. H. Feng, X. T. Feng, Y. Feng, Y. L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, W. K. Gao, M. M. Ge, T. T. Ge, L. S. Geng, G. Giacinti, G. H. Gong, Q. B. Gou, M. H. Gu, F. L. Guo, J. Guo, K. J. Guo, X. L. Guo, Y. Q. Guo, Y. Y. Guo, R. P. Han, O. A. Hannuksela, M. Hasan, H. H. He, H. N. He, J. Y. He, X. Y. He, Y. He, S. Hernández-Cadena, B. W. Hou, C. Hou, X. Hou, H. B. Hu, S. C. Hu, C. Huang, D. H. Huang, J. J. Huang, X. L. Huang, X. T. Huang, X. Y. Huang, Y. Huang, Y. Y. Huang, A. Inventar, X. L. Ji, H. Y. Jia, K. Jia, H. B. Jiang, K. Jiang, X. W. Jiang, Z. J. Jiang, M. Jin, S. Kaci, M. M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, Cheng Li, Cong Li, D. Li, F. Li, H. B. Li, H. C. Li, Jian Li, Jie Li, K. Li, L. Li, R. L. Li, S. D. Li, T. Y. Li, W. L. Li, X. R. Li, Xin Li, Y. Li, Zhe Li, Zhuo Li, E. W. Liang, Y. F. Liang, S. J. Lin, B. Liu, C. Liu, D. Liu, D. B. Liu, H. Liu, J. Liu, J. L. Liu, J. R. Liu, M. Y. Liu, R. Y. Liu, S. M. Liu, W. Liu, X. Liu, Y. Liu, Y. Liu, Y. N. Liu, Y. Q. Lou, Q. Luo, Y. Luo, H. K. Lv, B. Q. Ma, L. L. Ma, X. H. Ma, I. O. Maliy, J. R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G. B. Mou, A. Neronov, K. C. Y. Ng, M. Y. Ni, L. Nie, L. J. Ou, Z. W. Ou, P. Pattarakijwanich, Z. Y. Pei, D. Y. Peng, J. C. Qi, M. Y. Qi, J. J. Qin, D. Qu, A. Raza, C. Y. Ren, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y. Z. Shen, X. D. Sheng, Z. D. Shi, F. W. Shu, H. C. Song, Yu. V. Stenkin, V. Stepanov, Y. Su, D. X. Sun, H. Sun, J. X. Sun, Q. N. Sun, X. N. Sun, Z. B. Sun, N. H. Tabasam, J. Takata, P. H. T. Tam, H. B. Tan, Q. W. Tang, R. Tang, Z. B. Tang, W. W. Tian, C. N. Tong, L. H. Wan, C. Wang, D. H. Wang, G. W. Wang, H. G. Wang, J. C. Wang, K. Wang, Kai Wang, Kai Wang, L. P. Wang, L. Y. Wang, L. Y. Wang, R. Wang, W. Wang, X. G. Wang, X. J. Wang, X. Y. Wang, Y. Wang, Y. D. Wang, Z. H. Wang, Z. X. Wang, Zheng Wang, D. M. Wei, J. J. Wei, Y. J. Wei, T. Wen, S. S. Weng, C. Y. Wu, H. R. Wu, Q. W. Wu, S. Wu, X. F. Wu, Y. S. Wu, S. Q. Xi, J. Xia, J. J. Xia, G. M. Xiang, D. X. Xiao, G. Xiao, Y. F. Xiao, Y. L. Xin, H. D. Xing, Y. Xing, D. R. Xiong, B. N. Xu, C. Y. Xu, D. L. Xu, R. F. Xu, R. X. Xu, S. S. Xu, W. L. Xu, L. Xue, D. H. Yan, T. Yan, C. W. Yang, C. Y. Yang, F. F. Yang, L. L. Yang, M. J. Yang, R. Z. Yang, W. X. Yang, Z. H. Yang, Z. G. Yao, X. A. Ye, L. Q. Yin, N. Yin, X. H. You, Z. Y. You, Q. Yuan, H. Yue, H. D. Zeng, T. X. Zeng, W. Zeng, X. T. Zeng, M. Zha, B. B. Zhang, B. T. Zhang, C. Zhang, H. Zhang, H. M. Zhang, H. Y. Zhang, J. L. Zhang, J. Y. Zhang, Li Zhang, P. F. Zhang, R. Zhang, S. R. Zhang, S. S. Zhang, S. Y. Zhang, W. Zhang, W. Y. Zhang, X. Zhang, X. P. Zhang, Yi Zhang, Yong Zhang, Z. P. Zhang, J. Zhao, L. Zhao, L. Z. Zhao, S. P. Zhao, X. H. Zhao, Z. H. Zhao, F. Zheng, T. C. Zheng, B. Zhou, H. Zhou, J. N. Zhou, M. Zhou, P. Zhou, R. Zhou, X. X. Zhou, X. X. Zhou, B. Y. Zhu, C. G. Zhu, F. R. Zhu, H. Zhu, K. J. Zhu, Y. C. Zou, X. Zuo

TL;DR

This work reports the detection of extended very-high-energy to ultra-high-energy gamma-ray emission from the W43 star-forming region using LHAASO, with KM2A and WCDA data enabling detailed morphology and spectral analysis. The emission extends about $0.5^{\circ}$ (≈50 pc) and is best described by an elliptical Gaussian morphology; spectral modeling with NAIMA supports a hadronic scenario in which CR protons are accelerated in W43 and interact with ambient gas of density $n\approx 140\ \mathrm{cm^{-3}}$, yielding a total CR energy of about $2.5\times 10^{48}$ erg above 1 TeV and implying a CR density ~10× the local value. Hadronic models favor protons up to around $200$ TeV, differentiating from a simple leptonic explanation and aligning W43 with other extreme star-forming clusters such as Cygnus cocoon, though no clear PeV accelerator signature is required. The results highlight W43 as a potential second Galactic site of substantial high-energy CR acceleration, motivating future high-resolution gamma-ray and X-ray observations to resolve morphology and probe acceleration mechanisms in crowded star-forming regions.

Abstract

In this paper, we report the detection of the very-high-energy (VHE, $ 100{\rm\ GeV} < E < 100{\rm\ TeV} $) and ultra-high-energy (UHE, $E > 100\rm\ TeV$) $γ$-ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended $γ$-ray source was detected with a significance of ${\sim}16\,σ$ by KM2A and ${\sim}17\,σ$ by WCDA, respectively. The angular extension of this $γ$-ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the $γ$-ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.

Observation of the $γ$-ray Emission from W43 with LHAASO

TL;DR

This work reports the detection of extended very-high-energy to ultra-high-energy gamma-ray emission from the W43 star-forming region using LHAASO, with KM2A and WCDA data enabling detailed morphology and spectral analysis. The emission extends about (≈50 pc) and is best described by an elliptical Gaussian morphology; spectral modeling with NAIMA supports a hadronic scenario in which CR protons are accelerated in W43 and interact with ambient gas of density , yielding a total CR energy of about erg above 1 TeV and implying a CR density ~10× the local value. Hadronic models favor protons up to around TeV, differentiating from a simple leptonic explanation and aligning W43 with other extreme star-forming clusters such as Cygnus cocoon, though no clear PeV accelerator signature is required. The results highlight W43 as a potential second Galactic site of substantial high-energy CR acceleration, motivating future high-resolution gamma-ray and X-ray observations to resolve morphology and probe acceleration mechanisms in crowded star-forming regions.

Abstract

In this paper, we report the detection of the very-high-energy (VHE, ) and ultra-high-energy (UHE, ) -ray emissions from the direction of the young star-forming region W43, observed by the Large High Altitude Air Shower Observation (LHAASO). The extended -ray source was detected with a significance of by KM2A and by WCDA, respectively. The angular extension of this -ray source is about 0.5 degrees, corresponding to a physical size of about 50 pc. We discuss the origin of the -ray emission and possible cosmic ray acceleration in the W43 region using multi-wavelength data. Our findings suggest that W43 is likely another young star cluster capable of accelerating cosmic rays (CRs) to at least several hundred TeV.
Paper Structure (6 sections, 3 equations, 2 figures, 3 tables)

This paper contains 6 sections, 3 equations, 2 figures, 3 tables.

Table of Contents

  1. Introduction
  2. LHAASO DATA ANALYSIS AND RESULTS
  3. Data and analysis technique
  4. Results
  5. DISCUSSIONS
  6. CONCLUSIONS

Figures (2)

  • Figure 1: These figures display significance maps of W43 derived from the best-fit elliptical model. All sources, except LHAASO J1848-0153u, are subtracted with their best-fit parameters. Figure (a) shows the significance map in the energy range from 25 TeV to 100 TeV. The green and red '+' symbols indicate the best-fit positions of KM2A and WCDA, respectively, along with their corresponding $1\,\sigma$ statistical error bars. The solid ellipse represents the best-fit morphology of LHAASO J1848-0153u as determined by KM2A, while the dot-dash ellipse corresponds to that of WCDA. The parameters used to draw these elements are taken from the best-fit elliptical models with spectral parameters of GDE left free. Similarly, the blue '+' symbol and the dashed circle show results from the Fermi data yang20. The contour lines in black, dark green and bright green indicate gas column densities of $3$, $6$ and $10\times 10^{22} {\rm\ cm^{-2}}$yang20, respectively. Supernova Remnants (SNRs, marked by square symbols) from greensnr1 and pulsars (PSRs, marked by cross symbols) from ATNF pulsar catalogue atnf1atnf2 are also shown here. The positions of the two molecular clouds W43-main and W43-south, the TeV source HESS J1848-018 and the globular cluster GLIMPSE C01 are also plotted. Figure (b) shows the significance map in the energy range from 1 TeV to 25 TeV. Figure (c) shows the significance map in the energy range above 100 TeV.
  • Figure 2: Figure (a) shows the $\gamma$-ray spectra derived from the best-fit spectra of the parent particles, using the NAIMA package. Error bars with colors represent statistical errors, while the grey ones represent the systematic errors, primarily due to the challenges in understanding of the Galactic Diffuse Emission. The 95% confidence upper limits are indicated with downward arrows. 'MLL' represents the Maximum of Log(likelihood) in different models. In figure (a), the Fermi data points yang20 are also considered. In figure (b), we plotted bands by multiplying the best-fit proton spectra in both cases by 1.3 and 0.7, representing the uncertainties in gas density and pion decay cross-sections. They are also compared with the local proton spectrum measured by AMS ams_proton and DAMPE dampe_proton.