Accretion Torque Reversals in GRO J1008-57 Revealed by Insight-HXMT
Abstract
GRO J1008-57, as a Be/X-ray transient pulsar, is considered to have the highest magnetic field in known neutron star X-ray binary systems. Observational data of the X-ray outbursts in GRO J1008-57 from 2017 to 2020 were collected by the Insight-HXMT satellite. In this work, the spin period of the neutron star in GRO J1008-57 was determined to be about 93.28 seconds in August 2017, 93.22 seconds in February 2018, 93.25 seconds in June 2019 and 93.14 seconds in June 2020. GRO J1008-57 evolved in the spin-up process with a mean rate of 10 s/d from 2009 -- 2018, and turned into a spin down process with a rate of 10 s/d from Feb 2018 to June 2019. During the type II outburst of 2020, GRO J1008-57 had the spin-up torque again. During the torque reversals, the pulse profiles and continuum X-ray spectra did not change significantly, and the cyclotron resonant scattering feature around 80 keV was only detected during the outbursts in 2017 and 2020. Based on the observed mean spin-up rate, we estimated the inner accretion disk radius in GRO J1008-57 (about 1 - 2 times of the Alfv\'{e}n radius) by comparing different accretion torque models of magnetic neutron stars. During the spin-down process, the magnetic torque should dominate over the matter accreting inflow torque, and we constrained the surface dipole magnetic field G for the neutron star in GRO J1008-57, which is consistent with the magnetic field strength obtained by cyclotron line centroid energy.
Keywords
Cite
@article{arxiv.2102.12085,
title = {Accretion Torque Reversals in GRO J1008-57 Revealed by Insight-HXMT},
author = {W. Wang and Y. M. Tang and Y. L. Tuo and P. R. Epili and S. N. Zhang and L. M. Song and F. J. Lu and J. L. Qu and S. Zhang and M. Y. Ge and Y. Huang and B. Li and Q. C. Bu and C. Cai and X. L. Cao and Z. Chang and L. Chen and T. X. Chen and Y. B. Chen and Y. Chen and Y. P. Chen and W. W. Cui and Y. Y. Du and G. H. Gao and H. Gao and Y. D. Gu and J. Guan and C. C. Guo and D. W. Han and J. Huo and S. M. Jia and W. C. Jiang and J. Jin and L. D. Kong and C. K. Li and G. Li and T. P. Li and W. Li and X. Li and X. B. Li and X. F. Li and Z. W. Li and X. H. Liang and J. Y. Liao and B. S. Liu and C. Z. Liu and H. X. Liu and H. W. Liu and X. F. Lu and Q. Luo and T. Luo and R. C. Ma and X. Ma and B. Meng and Y. Nang and J. Y. Nie and G. Ou and X. Q. Ren and N. Sai and X. Y. Song and L. Sun and L. Tao and C. Wang and L. J. Wang and P. J. Wang and W. S. Wang and Y. S. Wang and X. Y. Wen and B. Y. Wu and B. B. Wu and M. Wu and G. C. Xiao and S. Xiao and S. L. Xiong and Y. P. Xu and R. J. Yang and S. Yang and J. J. Yang and Y. J. Yang and B. B. Yi and Q. Q. Yin and Y. You and F. Zhang and H. M. Zhang and J. Zhang and P. Zhang and W. Zhang and W. C. Zhang and Y. F. Zhang and Y. H. Zhang and H. S. Zhao and X. F. Zhao and S. J. Zheng and Y. G. Zheng and D. K. Zhou},
journal= {arXiv preprint arXiv:2102.12085},
year = {2021}
}
Comments
10 pages, 5 figures, and 3 tables, the Journal of High Energy Astrophysics in press