Insight-HXMT Firm Detection of the Highest-energy Fundamental Cyclotron Resonance Scattering Feature in the Spectrum of GRO J1008-57

Ming-Yu Ge ,R Staubert,C M Zhang,C K Li,M S Li,C Z Liu,A M Zhang,X Li,G Ou,A Santangelo,J Guan,J L Qu,Y D Gu,Y S Wang,T P Li,Y Y Du,Q B Yi,W Li,Q Luo,R C Shang,W C Zhang,X H Liang,Y N Liu,B B Wu,G H Gao,L J Wang,W Z Zhang,X B Li,Y You,Y G Li,G Li,G Chen,C Cai,T Zhang,S M Jia,X F Zhao,J Jin,J Zhang,B Y Wu,L D Kong,Y B Chen,W S Wang,X J Liu,G C Xiao,C Wang,Z W Li,S Yang,M X Fu,J Wang,T X Chen,Q C Bu,B Lu,Z L Zhang,J K Deng,S Zhang,D K Zhou,Y Huang,H M Zhang,Y P Chen,B Li,J Y Liao,Z Zhang,X F Li,F J Lu,Y Zhang,G F Wang,X Y Song,X F Lu,L Chen,Y J Zhang,X L Cao,N Sai,Y G Zheng,Y Chen,Q Q Yin,J Y Nie,R L Zhuang,Y F Zhang,S L Xiong,W Zhang,Y Nang,Y D Wang,G Q Liu,T Luo,Zhi Chang ,You-Li Tuo ,Yuxuan Zhu ,Bai-Sheng Liu ,Ying Xu ,Min Gao ,Liming Song ,Lian Tao ,Victor Doroshenko ,Han–Wen Liu ,Chengcheng Guo ,Weiwei Cui ,Long Ji ,Heng Xu ,Yan Jin ,Bin Meng ,Zhaojian Zhang ,Shuang‐Nan Zhang ,Yun-Cheng Yang ,Jiawei Yang ,Gao H ,Liang Sun ,Jianfeng Zhou ,Danxiang Han ,H Zhao ,Mei‐Hwan Wu ,Weichun Jiang ,Y H Tan ,Yongwei Dong ,Wei Cui ,Faming Zhang ,Shi-Jie Zheng ,Shuo Xiao ,Xiang-Yang Wen ,Haiqiang Jia ,Luhua Jiang ,Xiang Ma

doi:10.3847/2041-8213/abac05

Abstract

Abstract We report on the observation of the accreting pulsar GRO J1008-57 performed by Insight-Hard X-ray Modulation Telescope (HXMT) at the peak of the source’s 2017 outburst. Pulsations are detected with a spin period of 93.283(1) s. The pulse profile shows double peaks at soft X-rays, and only one peak above 20 keV. The spectrum is well described by the phenomenological models of X-ray pulsars. A cyclotron resonant scattering feature (CRSF) is detected with very high statistical significance at a centroid energy of keV, for the reference continuum and line models, HIGHECUT and GABS, respectively. Detection is very robust with respect to different continuum models. The line energy is significantly higher than what is suggested from previous observations, which provided very marginal evidence for the line. This establishes a new record for the centroid energy of a fundamental CRSF observed in accreting pulsars. We also discuss the accretion regime of the source during the Insight-HXMT observation.

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