2020A&A...634A..99K

We present an analysis of X-ray spectra of the high-mass X-ray binary 4U 0115+634 as observed with Suzaku and RXTE in 2011 July, during the fading phase of a giant X-ray outburst. We used a continuum model consisting of an absorbed cutoff power law and an ad hoc Gaussian emission feature centered around 8.5keV, which we attribute to cyclotron emission. Our results are consistent with a fundamental cyclotron absorption line centered at ∼10.2keV for all observed flux ranges. At the same time we rule out significant influence of the 8.5kev Gaussian on the parameters of the cyclotron resonant scattering feature, which are not consistent with the cyclotron line energies or the depths of previously reported flux-dependent descriptions. We also show that some continuum models can lead to artificial line-like residuals in the analyzed spectra, which are then misinterpreted as unphysically strong cyclotron lines. Specifically, our results do not support the existence of a previously claimed additional cyclotron feature at ∼15keV. Apart from these features, we find for the first time evidence for a He-like FeXXV emission line at ∼6.7keV and weak H-like FeXXVI emission close to ∼7.0keV.