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Deep view of Composite SNR CTA1 with LHAASO in $γ$-rays up to 300 TeV

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, B. Li

TL;DR

This study uses LHAASO data spanning 2019–2023 to deeply characterize 1LHAASO J0007+7303u, associated with the composite SNR CTA1. A forward-folded maximum-likelihood analysis shows the source is extended and well described by a power law with exponential cutoff, $dN/dE= N_0 (E/20\,0\mathrm{TeV})^{-\alpha} e^{-E/E_c}$, with $\alpha=2.31\pm0.13$ and $E_c=110\pm25$ TeV, across $8-300$ TeV; the 8–100 TeV and $>100$ TeV bands yield significances of $\sim21\sigma$ and $\sim17\sigma$, respectively. The inferred steady-state electron spectrum above $\sim50$ TeV is $dN_e/dE_e \propto (E_e/100\ \mathrm{TeV})^{-3.13\pm0.16} \exp[-(E_e/373\ \mathrm{TeV})^2]$, with a current PWN magnetic field of $B\approx4.5\ \mu$G, implying efficient leptonic IC scattering (predominantly on the CMB) in a relatively low-field environment. Transport modeling favors advection-dominated particle flow in the PWN during the (near) free-expansion phase, and disfavors pure diffusion as the sole mechanism; the results support a leptonic origin for the UHE emission and provide a direct constraint on the electron spectrum and the termination-shock acceleration capability of CTA1.

Abstract

The ultra-high-energy (UHE) gamma-ray source 1LHAASO J0007+7303u is positionally associated with the composite SNR CTA1 that is located at high Galactic Latitude $b\approx 10.5^\circ$. This provides a rare opportunity to spatially resolve the component of the pulsar wind nebula (PWN) and supernova remnant (SNR) at UHE. This paper conducted a dedicated data analysis of 1LHAASO J0007+7303u using the data collected from December 2019 to July 2023. This source is well detected with significances of 21$σ$ and 17$σ$ at 8$-$100 TeV and $>$100 TeV, respectively. The corresponding extensions are determined to be 0.23$^{\circ}\pm$0.03$^{\circ}$ and 0.17$^{\circ}\pm$0.03$^{\circ}$. The emission is proposed to originate from the relativistic electrons and positrons accelerated within the PWN of PSR J0007+7303. The energy spectrum is well described by a power-law with an exponential cutoff function $dN/dE = (42.4\pm4.1)(\frac{E}{20\rm\ TeV})^{-2.31\pm0.11}\exp(-\frac{E}{110\pm25\rm\ TeV})$ $\rm\ TeV^{-1}\ cm^{-2}\ s^{-1}$in the energy range from 8 TeV to 300 TeV, implying a steady-state parent electron spectrum $dN_e/dE_e\propto (\frac{E_e}{100\rm\ TeV})^{-3.13\pm0.16}\exp[(\frac{-E_e}{373\pm70\rm\ TeV})^2]$ at energies above $\approx 50 \rm\ TeV$. The cutoff energy of the electron spectrum is roughly equal to the expected current maximum energy of particles accelerated at the PWN terminal shock. Combining the X-ray and gamma-ray emission, the current space-averaged magnetic field can be limited to $\approx 4.5\rm\ μG$. To satisfy the multi-wavelength spectrum and the $γ$-ray extensions, the transport of relativistic particles within the PWN is likely dominated by the advection process under the free-expansion phase assumption.

Deep view of Composite SNR CTA1 with LHAASO in $γ$-rays up to 300 TeV

TL;DR

This study uses LHAASO data spanning 2019–2023 to deeply characterize 1LHAASO J0007+7303u, associated with the composite SNR CTA1. A forward-folded maximum-likelihood analysis shows the source is extended and well described by a power law with exponential cutoff, , with and TeV, across TeV; the 8–100 TeV and TeV bands yield significances of and , respectively. The inferred steady-state electron spectrum above TeV is , with a current PWN magnetic field of G, implying efficient leptonic IC scattering (predominantly on the CMB) in a relatively low-field environment. Transport modeling favors advection-dominated particle flow in the PWN during the (near) free-expansion phase, and disfavors pure diffusion as the sole mechanism; the results support a leptonic origin for the UHE emission and provide a direct constraint on the electron spectrum and the termination-shock acceleration capability of CTA1.

Abstract

The ultra-high-energy (UHE) gamma-ray source 1LHAASO J0007+7303u is positionally associated with the composite SNR CTA1 that is located at high Galactic Latitude . This provides a rare opportunity to spatially resolve the component of the pulsar wind nebula (PWN) and supernova remnant (SNR) at UHE. This paper conducted a dedicated data analysis of 1LHAASO J0007+7303u using the data collected from December 2019 to July 2023. This source is well detected with significances of 21 and 17 at 8100 TeV and 100 TeV, respectively. The corresponding extensions are determined to be 0.230.03 and 0.170.03. The emission is proposed to originate from the relativistic electrons and positrons accelerated within the PWN of PSR J0007+7303. The energy spectrum is well described by a power-law with an exponential cutoff function in the energy range from 8 TeV to 300 TeV, implying a steady-state parent electron spectrum at energies above . The cutoff energy of the electron spectrum is roughly equal to the expected current maximum energy of particles accelerated at the PWN terminal shock. Combining the X-ray and gamma-ray emission, the current space-averaged magnetic field can be limited to . To satisfy the multi-wavelength spectrum and the -ray extensions, the transport of relativistic particles within the PWN is likely dominated by the advection process under the free-expansion phase assumption.
Paper Structure (14 sections, 14 equations, 7 figures, 5 tables)

This paper contains 14 sections, 14 equations, 7 figures, 5 tables.

Table of Contents

  1. Introduction
  2. LHAASO Data Analysis
  3. Data selection and binning
  4. Maximum Likelihood Analysis and Statistic Test
  5. Results
  6. Morphology
  7. Morphology
  8. Spectrum
  9. Systematic Uncertainties
  10. Discussion
  11. The Nature of the $\gamma$-ray emission detected by LHAASO
  12. The broad-band spectrum: implications for the magnetic field and particle spectrum
  13. The Morphology: implications for propagation mechanism
  14. Conclusions

Figures (7)

  • Figure 1: The significance maps of CTA1 in the energy ranges of $8{\rm\ TeV}<E < 100\rm\ TeV$ (a) and $E > 100\rm\ TeV$ (b). Overlaid are the GB6 image countour (4850MHz) in gray. Cyan stars represent the position of the pulsar PSR J0007+7303.
  • Figure 2: LHAASO differential $\gamma$-ray spectrum of the PWN CTA1. The red line and the orange butterfly represent the best-fit PLC model and its uncertainties, respectively.
  • Figure 3: Multi-wavelength observations in CTA1 region. The circles represent 39% flux region. The dashed circle represents the lower limit of the extension. The size of the X-ray PWN has not been determined to date. The non-thermal X-ray emission is detected by ASCA in the $0.3^\circ$ region around the pulsar. Conservatively, the lower limit radius of the 39% X-ray flux region is estimated to $0.15^\circ$, assuming a Gaussian flux distribution.
  • Figure 4: The differential energy spectrum of the PWN CTA1. The red line represents the expectation from a one-zone leptonic model, assuming a magnetic field strength of 4.5 $\mu G$ and considering only CMB target photons. The electron spectrum follows a broken power law distribution, where $dN_e/dE_e \propto E_e^{-3.13}\exp[-(E_e/373\rm\ TeV)^2]$ for energies $E> 40\rm\ TeV$ and $dN_e/dE_e \propto E_e^{-2.13}$ for energies $E< 40\rm\ TeV$. The time-dependent model (pure advection scenario) is referenced in the Appendix.
  • Figure 5: The $\gamma$-ray extensions of the PWN CTA1. The simulated extension corresponds to the 39% flux size, which means that the flux inside this region is 39% of the total flux in the PWN. The black and grey dashed lines represent the extension calculated by the pure advection and pure diffusion scenarios.
  • ...and 2 more figures