A peculiar cyclotron line near 16 keV detected in the 2015 outburst of 4U 0115+63?

In 2015 October, the Be/X-ray binary 4U 0115+63 underwent a type II outburst, reaching an X-ray luminosity of similar to 10(38)erg s(-1). During the outburst, Nuclear Spectroscopic Telescope Array (NuSTAR) performed two Target of Opportunity observations. Using the broadband spectra from NuSTAR (3-79 keV), we have detected multiple cyclotron lines of the source, i.e., similar to 12, 16, 22, and 33/35 keV. Obviously, the 16 keV line is not a harmonic component of the 12 keV line. As described by the phase-dependent equivalent widths of these cyclotron lines, the 16 keV and 12 keV lines are two different fundamental lines. In our work, we apply the two-poles cyclotron line model to the observation, i.e., the two line sets are formed at the same altitude (similar to 0.2 km over the NS surface) of different magnetic poles, with similar to 1.1 x 10(12)and 1.4 x 10(12)G in two poles, respectively.