QPOs and Orbital elements of X-ray binary 4U 0115+63 during the 2017 outburst observed by Insight-HXMT

Y. Z. Ding, W. Wang, P. Zhang, Q. C. Bu, C. Cai, X. L. Cao, C. Zhi, L. Chen, T. X. Chen, Y. B. Chen, Y. Chen, Y. P. Chen, W. W. Cui, Y. Y. Du, G. H. Gao, H. Gao, M. Y. Ge, Y. D. Gu, J. Guan, C. C. Guo, D. W. Han, Y. Huang, J. Huo, S. M. Jia, W. C. Jiang, J. Jin, L. D. Kong, B. Li, C. K. Li, G. Li, T. P. Li, W. Li, X. Li, X. B. Li, X. F. Li, Z. W. Li, X. H. Liang, J. Y. Liao, B. S. Liu, C. Z. Liu, H. X. Liu, H. W. Liu, X. J. Liu, F. J. Lu, X. F. Lu, Q. L., L. T., R. C. Ma, X. Ma, B. Meng, Y. Nang, J. Y. Nie, J. L. Qu, X. Q. Ren, N. Sai, L. M. Song, X. Y. Song, L. Sun, Y. Tan, L. Tao, Y. L. Tuo, L. J. Wang, P. J. Wang, W. S. Wang, Y. S. Wang, X. Y. Wen, B. Y. Wu, B. B. Wu, M. Wu, G. C. Xiao, S. Xiao, S. L. Xiong, Y. P. Xu, R. J. Yang, S. Yang, Y. J. Yang, Q. B. Yi, Q. Q. Yin, Y. You, F. Zhang, H. M. Zhang, J. Zhang, P. Zhang, S. Zhang, S. N. Zhang, W. C. Zhang, W. Zhang, Y. F. Zhang, Y. H. Zhang, H. S. Zhao, X. F. Zhao, S. J. Zheng, Y. G. Zheng, D. K. Zhou

Published 2021-02-18Version 1

In this paper, we presented a detailed timing analysis of a prominent outburst of 4U 0115+63 detected by \textit{Insight}-HXMT in 2017 August. The spin period of the neutron star was determined to be $3.61398\pm 0.00002$ s at MJD 57978. We measured the period variability and extract the orbital elements of the binary system. The angle of periastron evolved with a rate of $0.048\pm0.003$ $yr^{-1}$. The light curves are folded to sketch the pulse profiles in different energy ranges. A multi-peak structure in 1-10 keV is clearly illustrated. We introduced wavelet analysis into our data analysis procedures to study QPO signals and perform a detailed wavelet analysis in many different energy ranges. Through the wavelet spectra, we report the discovery of a QPO at the frequency $\sim 10$ mHz. In addition, the X-ray light curves showed multiple QPOs in the period of $\sim 16-32 $ s and $\sim 67- 200 $ s. We found that the $\sim100$ s QPO was significant in most of the observations and energies. There exist positive relations between X-ray luminosity and their Q-factors and S-factors, while the QPO periods have no correlation with X-ray luminosity. In wavelet phase maps, we found that the pulse phase of $\sim 67- 200 $ s QPO drifting frequently while the $\sim 16-32 $ s QPO scarcely drifting. The dissipation of oscillations from high energy to low energy was also observed. These features of QPOs in 4U 0115+63 provide new challenge to our understanding of their physical origins.