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

In this paper, we presented a detailed timing analysis of a prominent outburst of 4U 0115+63 detected by Insight-IDCMT 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 degrees +/- 0.003 degrees 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 similar to 10 mHz. In addition, the X-ray light curves showed multiple QPOs in the period of similar to 16-32 and similar to 67-200 s. We found that the similar to 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 similar to 67-200 s QPO is drifting frequently while that of similar to 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.