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Discovery of a new $γ$-ray source LHAASO J0341+5258 with emission up to 200TeV

The LHAASO Collaboration, Zhen Cao, F. Aharonian, Q. An, Axikegu, L. X. Bai, Y. X. Bai, Y. W. Bao, D. Bastieri, X. J. Bi, Y. J. Bi, H. Cai, J. T. Cai, Zhe Cao, J. Chang, J. F. Chang, B. M. Chen, E. S. Chen, J. Chen, Liang Chen, Liang Chen, Long Chen, M. J. Chen, M. L. Chen, Q. H. Chen, S. H. Chen, S. Z. Chen, T. L. Chen, X. L. Chen, Y. Chen, N. Cheng, Y. D. Cheng, S. W. Cui, X. H. Cui, Y. D. Cui, B. D Ettorre Piazzoli, B. Z. Dai, H. L. Dai, Z. G. Dai, Danzengluobu, D. della Volpe, X. J. Dong, K. K. Duan, J. H. Fan, Y. Z. Fan, Z. X. Fan, J. Fang, K. Fang, C. F. Feng, L. Feng, S. H. Feng, Y. L. Feng, B. Gao, C. D. Gao, L. Q. Gao, Q. Gao, W. Gao, M. M. Ge, L. S. Geng, G. H. Gong, Q. B. Gou, M. H. Gu, F. L. Guo, J. G. Guo, X. L. Guo, Y. Q. Guo, Y. Y. Guo, Y. A. Han, H. H. He, H. N. He, J. C. He, S. L. He, X. B. He, Y. He, M. Heller, Y. K. Hor, C. Hou, H. B. Hu, S. Hu, S. C. Hu, X. J. Hu, D. H. Huang, Q. L. Huang, W. H. Huang, X. T. Huang, X. Y. Huang, Z. C. Huang, F. Ji, X. L. Ji, H. Y. Jia, K. Jiang, Z. J. Jiang, C. Ji, T. Ke, D. Kuleshov, K. Levochkin, B. B. Li, Cheng Li, Cong Li, F. Li, H. B. Li, H. C. Li, H. Y. Li, J. Li, K. Li, W. L. Li, X. R. Li, Xin Li, Xin Li, Y. Li, Y. Z. Li, Zhe Li, Zhuo Li, E. W. Liang, Y. F. Liang, S. J. Lin, B. Liu, C. Liu, D. Liu, H. Liu, H. D. Liu, J. Liu, J. L. Liu, J. S. Liu, J. Y. Liu, M. Y. Liu, R. Y. Liu, S. M. Liu, W. Liu, Y. Liu, Y. N. Liu, Z. X. Liu, W. J. Long, R. Lu, H. K. Lv, B. Q. Ma, L. L. Ma, X. H. Ma, J. R. Mao, A. Masood, Z. Min, W. Mitthumsiri, T. Montaruli, Y. C. Nan, B. Y. Pang, P. Pattarakijwanich, Z. Y. Pei, M. Y. Qi, Y. Q. Qi, B. Q. Qiao, J. J. Qin, D. Ruffolo, V. Rulev, A. Saiz, L. Shao, O. Shchegolev, X. D. Sheng, J. Y. Shi, H. C. Song, Yu. V. Stenkin, V. Stepanov, Y. Su, Q. N. Sun, X. N. Sun, Z. B. Sun, P. H. T. Tam, Z. B. Tang, W. W. Tian, B. D. Wang, C. Wang, H. Wang, H. G. Wang, J. C. Wang, J. S. Wang, L. P. Wang, L. Y. Wang, R. N. Wang, W. Wang, W. Wang, X. G. Wang, X. J. Wang, X. Y. Wang, Y. Wang, Y. D. Wang, Y. J. Wang, Y. P. Wang, Z. H. Wang, Z. . Wang, Zhen Wang, Zheng Wang, D. M. Wei, J. J. Wei, Y. J. Wei, T. Wen, C. Y. Wu, H. R. Wu, S. Wu, W. X. Wu, X. F. Wu, S. Q. Xi, J. Xia, J. J. Xia, G. M. Xiang, D. X. Xiao, G. Xiao, H. B. Xiao, G. G. Xin, Y. L. Xin, Y. Xing, D. L. Xu, R. X. Xu, L. Xue, D. H. Yan, J. Z. Yan, C. W. Yang, F. F. Yang, J. Y. Yang, L. L. Yang, M. J. Yang, R. Z. Yang, S. B. Yang, Y. H. Yao, Z. G. Yao, Y. M. Ye, L. Q. Yin, N. Yin, X. H. You, Z. Y. You, Y. H. Yu, Q. Yuan, H. D. Zeng, T. X. Zeng, W. Zeng, Z. K. Zeng, M. Zha, X. X. Zhai, B. B. Zhang, H. M. Zhang, H. Y. Zhang, J. L. Zhang, J. W. Zhang, L. X. Zhang, Li Zhang, Lu Zhang, P. F. Zhang, P. P. Zhang, R. Zhang, S. R. Zhang, S. S. Zhang, X. Zhang, X. P. Zhang, Y. F. Zhang, Y. L. Zhang, Yi Zhang, Yong Zhang, B. Zhao, J. Zhao, L. Zhao, L. Z. Zhao, S. P. Zhao, F. Zheng, Y. Zheng, B. Zhou, H. Zhou, J. N. Zhou, P. Zhou, R. Zhou, X. X. Zhou, C. G. Zhu, F. R. Zhu, H. Zhu, K. J. Zhu, X. Zuo

TL;DR

This study reports the discovery of LHAASO J0341+5258, a bright, extended gamma-ray source in the Galactic plane with emission up to $200\ \mathrm{TeV}$. Using 2369 hours of KM2A data, the source is detected above $25\ \mathrm{TeV}$ with a significance of ${8.2\sigma}$ (pre-trial) and is resolved as extended with ${\sigma_{\rm ext}=0.29^{\circ}}$, located at ${\rm RA}=55.34^{\circ}$, ${\rm Dec}=52.97^{\circ}$. The spectrum from ${\sim}10$ to ${\sim}200\ \mathrm{TeV}$ is consistent with a power-law of index ${\alpha=2.98\pm0.19_{stat}\pm0.02_{sys}}$, though a mild curvature fits the data better via a log-parabola; the integral flux above ${25\ \mathrm{TeV}}$ is ${1.43\times10^{-14}}\ \mathrm{cm^{-2}\,s^{-1}}$ (~${20\%}$ of the Crab Nebula). Multiwavelength analysis, including Fermi-LAT, X-ray, and CO/IR data, suggests possible leptonic (PWN/pulsar halo) or hadronic scenarios, but no clearly energetic pulsar or young SNR is identified to anchor a definitive origin. The contemporaneous Fermi-LAT analysis indicates a curved GeV spectrum for the nearby LAT source 4FGL J0340.4+5302 and demonstrates that its GeV emission is not straightforwardly connected to the TeV source, underscoring the need for further deep, multiwavelength observations to distinguish between leptonic and hadronic processes.

Abstract

We report the discovery of a new unidentified extended $γ$-ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A.$=55.34^{\circ}\pm0.11^{\circ}$ and Dec$=52.97^{\circ}\pm0.07^{\circ}$. The angular size of LHAASO J0341+5258 is $0.29^\circ \pm 0.06^\circ_{stat} \pm0.02^\circ_{sys}$. The flux above 25 TeV is about $20\%$ of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index $α=2.98 \pm 0.19_{stat} \pm 0.02_{sys}$ is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %($α\leq 1.75$) spectrum with a cutoff at $\approx 50$ TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production.

Discovery of a new $γ$-ray source LHAASO J0341+5258 with emission up to 200TeV

TL;DR

This study reports the discovery of LHAASO J0341+5258, a bright, extended gamma-ray source in the Galactic plane with emission up to . Using 2369 hours of KM2A data, the source is detected above with a significance of (pre-trial) and is resolved as extended with , located at , . The spectrum from to is consistent with a power-law of index , though a mild curvature fits the data better via a log-parabola; the integral flux above is (~ of the Crab Nebula). Multiwavelength analysis, including Fermi-LAT, X-ray, and CO/IR data, suggests possible leptonic (PWN/pulsar halo) or hadronic scenarios, but no clearly energetic pulsar or young SNR is identified to anchor a definitive origin. The contemporaneous Fermi-LAT analysis indicates a curved GeV spectrum for the nearby LAT source 4FGL J0340.4+5302 and demonstrates that its GeV emission is not straightforwardly connected to the TeV source, underscoring the need for further deep, multiwavelength observations to distinguish between leptonic and hadronic processes.

Abstract

We report the discovery of a new unidentified extended -ray source in the Galactic plane named LHAASO J0341+5258 with a pre-trial significance of 8.2 standard deviations above 25 TeV. The best fit position is R.A. and Dec. The angular size of LHAASO J0341+5258 is . The flux above 25 TeV is about of the flux of Crab Nebula. Although a power-law fit of the spectrum from 10 TeV to 200 TeV with the photon index is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum %() spectrum with a cutoff at TeV. We briefly discuss the origin of UHE gamma-rays. The lack of an energetic pulsar and a young SNR inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude both the leptonic and hadronic scenarios of gamma-ray production.

Paper Structure

This paper contains 8 sections, 1 equation, 5 figures.

Table of Contents

  1. Introduction
  2. The LHAASO-KM2A experiment
  3. Analysis and Results
  4. Discussions
  5. Multiwavelength observations
  6. Phenomenological fitting and possible origin
  7. Conclusions
  8. Fermi-LAT analysis

Figures (5)

  • Figure 1: The significance map of LHAASO J0341+5258 above 25 TeV. The green circle marks the position of 4FGL J0340.4+5302, and the blue cross marks the position of the pulsar PSR J0343+5312. The white circle at the bottom-right corner shows the size of the PSF ($68\%$ containment). The PSF value is $0.40^{\circ}$ above 25 TeV.
  • Figure 2: Distribution of events as a function of the square of the angular distance to the LHAASO J0341+5258 direction for both experimental data (black points) and MC simulation (green area). Events with energy above 25 TeV are used here.
  • Figure 3: The energy spectrum of LHAASO J0341+5258. Only statistic errors are shown here. The solid line is the best fit result assuming a single power-law function and the dotted line is the result from log-parabola function.
  • Figure 4: WISE 12$\mu$m emission and CO emission (green contours) toward LHAASO J0341+5258 (the golden cycle). The CO emission is integrated in the velocity interval of 0--10 km s$^{-1}$ and starts from 1.5 K km s$^{-1}$ with a step of 1.5 K km s$^{-1}$. The yellow-dashed line marks the half-shell CO structure. The cyan box indicates PSR J0343+5312.
  • Figure 5: The multiwavelength SEDs of LHAASO J0341+5258. The black squares are the LHAASO KM2A observations, the red points and arrows are the Fermi LAT spectral points and upper limits, the green and blue point is the X-ray flux for 2SXPS 171354 and 2SXPS 172133 from the 2RXPS catalog 2020yCat.9058....0E, respectively. The black arrow labels the upper limit derived from Chandra observations. The gray arrow is the HAWC upper limit from the online interactive tools (see the text for detail). Also shown is the phenomenological fitting in both leptonic (black curves) and hadronic scenarios (red curves).