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

• Published in: Monthly notices of the Royal Astronomical Society Vol. 503; no. 4; pp. 6045 - 6058
• Main Authors: Ding, Y Z, Wang, W, Zhang, P, Bu, Q C, Cai, C, Cao, X L, Zhi, C, Chen, L, Chen, T X, Chen, Y B, Chen, Y, Chen, Y P, Cui, W W, Du, Y Y, Gao, G H, Gao, H, Ge, M Y, Gu, Y D, Guan, J, Guo, C C, Han, D W, Huang, Y, Huo, J, Jia, S M, Jiang, W C, Jin, J, Kong, L D, Li, B, Li, C K, Li, G, Li, T P, Li, W, Li, X, Li, X B, Li, X F, Li, Z W, Liang, X H, Liao, J Y, Liu, B S, Liu, C Z, Liu, H X, Liu, H W, Liu, X J, Lu, F J, Lu, X F, Lou, Q, Luo, T, Ma, R C, Ma, X, Meng, B, Nang, Y, Nie, J Y, Qu, J L, Ren, X Q, Sai, N, Song, L M, Song, X Y, Sun, L, Tan, Y, Tao, L, Tuo, Y L, Wang, C, Wang, L J, Wang, P J, Wang, W S, Wang, Y S, Wen, X Y, Wu, B Y, Wu, B B, Wu, M, Xiao, G C, Xiao, S, Xiong, S L, Xu, Y P, Yang, R J, Yang, S, Yang, Y J, Yi, Q B, Yin, Q Q, You, Y, Zhang, F, Zhang, H M, Zhang, J, Zhang, S, Zhang, S N, Zhang, W C, Zhang, W, Zhang, Y F, Zhang, Y H, Zhao, H S, Zhao, X F, Zheng, S J, Zheng, Y G, Zhou, D K
• Format: Journal Article
• Language: English
• Published: Oxford University Press 01-06-2021
• Subjects: X-rays: binaries; stars: individual: 4U 0115+63; X-rays: stars
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stab835

ABSTRACT
In this paper, we presented a detailed timing analysis of a prominent outburst of 4U 0115+63 detected by Insight-HXMT in 2017 August. The spin period of the neutron star was determined to be 3.613 98 ± 0.000 02 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 $0.048^\circ \pm 0.003^\circ \rm \, yr^{-1}$. The light curves are folded to sketch the pulse profiles in different energy ranges. A multipeak structure in 1–10 keV is clearly illustrated. We introduced wavelet analysis into our data analysis procedures to study quasi-periodic oscillation (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 of ∼10 mHz. In addition, the X-ray light curves showed multiple QPOs in the period of ∼16–32 and ∼67–200 s. We found that the ∼100 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 ∼67–200 s QPO is drifting frequently while that of ∼16–32 s QPO is scarcely drifting. The dissipation of oscillations from high energy to low energy was also observed. These features of QPOs in 4U 0115+63 provide a new challenge to our understanding of their physical origins.