Observation of Gamma Rays up to 320 TeV from the Middle-aged TeV Pulsar Wind Nebula HESS J1849−000
M. Amenomori, Shigeru Asano, Y. W. Bao, Xiao-Jun Bi, D. Chen, T. L. Chen, Wen‐Yun Chen, Xu Chen, Ye Chen, Cirennima, S. W. Cui, Danzengluobu Danzengluobu, L. K. Ding, J. Fang, Kun Fang, C. Feng, Zhaoyang Feng, Z. Y. Feng, Qi Gao, A. Gomi, Q. B. Gou, Yi-Qing Guo, Y. Y. Guo, Y. Hayashi, H. H. He, Z. T. He, K. Hibino, N. Hotta, Haibing Hu, H. B. Hu, Kun Hu, J. Huang, H. Y. Jia, Long Jiang, Ping Jiang, H.-B. Jin, K. Kasahara, Y. Katayose, C. Kato, Shinsuke Kato, Ichiro Kawahara, Tomohisa Kawashima, K. Kawata, M. Kozai, D. Kurashige, Labaciren Labaciren, G. M. Le, A. F. Li, H. J. Li, Wenjuan Li, Y. Li, Y. H. Lin, Jianwei Liu, Cheng Liu, J. S. Liu, L. Y. Liu, M. Y. Liu, W. Liu, H. Lu, X. R. Meng, Yanfeng Meng, K. Munakata, K. Nagaya, Yuya Nakamura, Y. Nakazawa, H. Nanjo, C. C. Ning, M. Nishizawa, Rina Noguchi, M. Ohnishi, S. Okukawa, S. Ozawa, Xuan Qian, Xuan Qian, X. B. Qu, T. Saito, Yoshiaki Sakakibara, M. Sakata, T. Sako, T. Sako, T. Sasaki, Jie Shao, M. Shibata, A. Shiomi, H. Sugimoto, W. Takano, M. Takita, Y. H. Tan, N. Tateyama, S. Torii, H. Tsuchiya, S. Udo, Hui Wang, S. F. Wang, Y. P. Wang, Wangdui, H. R. Wu, Qingwen Wu, Jun Xu, L. Xue
Abstract
Abstract Gamma rays from HESS J1849−000, a middle-aged TeV pulsar wind nebula (PWN), are observed by the Tibet air shower array and the muon detector array. The detection significance of gamma rays reaches 4.0 σ and 4.4 σ levels above 25 TeV and 100 TeV, respectively, in units of the Gaussian standard deviation σ . The energy spectrum measured between 40 TeV < E < 320 TeV for the first time is described with a simple power-law function of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">dN</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="italic">dE</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mn>2.86</mml:mn> <mml:mo>±</mml:mo> <mml:mn>1.44</mml:mn> <mml:mo stretchy="false">)</mml:mo> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>16</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>E</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>40</mml:mn> <mml:mspace width="0.25em"/> <mml:mi>TeV</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.24</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.41</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>TeV</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi>cm</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . The gamma-ray energy spectrum from the sub-TeV ( E < 1 TeV) to sub-PeV (100 TeV < E < 1 PeV) ranges, including the results of previous studies, can be modeled with the leptonic scenario, i.e., inverse Compton scattering by high-energy electrons accelerated by the PWN of PSR J1849−0001. On the other hand, the gamma-ray energy spectrum can also be modeled with the hadronic scenario in which gamma rays are generated from the decay of neutral pions produced by collisions between accelerated cosmic-ray protons and the ambient molecular cloud found in the gamma-ray-emitting region. The cutoff energy of cosmic-ray protons E p,cut is estimated as <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>log</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">p</mml:mi> <mml:mo>,</mml:mo> <mml:mi>cut</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>TeV</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>3.73</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.66</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.98</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , suggesting that protons are accelerated up to the PeV energy range. Our study thus proposes that HESS J1849−000 should be further investigated as a new candidate as a Galactic PeV cosmic-ray accelerator, or “PeVatron.”