Unfolded phase averaged spectra along with best-fitting continuum model shown in the figure in inset (a). We show the spectral residuals obtained with various phenomenological models such as: (b) an absorbed cutoffpl model, (c) an absorbed power law model with a high-energy exponential cutoff, (d) an absorbed two component power law model with a negative and positive exponential cutoff, (e) the best-fitting absorbed cutoff power law model with a cyclotron absorption line component in hard X-rays. The absorption feature in hard X-rays is fit with a multiplicative cyclotron line absorption component (cyclabs in Xspec). The error bars represent 1σ uncertainties. In the inset (a), the observation ID is shown on the right side of the panel. Corresponding epochs of the Insight-HXMT observations can be seen from Table A.1 in the appendix.