  Cyclotron resonant scattering features are an essential tool for studying the
magnetic field of neutron stars. The fundamental line provides a measure of the
field strength, while the harmonic lines provide information about the
structure and configuration of the magnetic field. Until now only a handful of
sources are known to display more than one cyclotron line and only two of them
have shown a series of harmonics. The aim of this work is to see the first
harmonic cyclotron line, confirming the fundamental line at around 22 keV, thus
increasing the number of sources with detected harmonic cyclotron lines. To
investigate the presence of absorption or emission lines in the spectra, we
have combined RXTE and INTEGRAL spectra. We modeled the 3-100 keV continuum
emission with a power law with an exponential cut off and look for the second
absorption feature. We show evidence of an unknown cyclotron line at around 47
keV (the first harmonic) in the phase-averaged X-ray spectra of 4U 1538-52.
This line is detected by several telescopes at different epochs, even though
the signal-to-noise ratio of each individual spectrum is low. We conclude that
the line-like absorption is a real feature, and the most straightforward
interpretation is that it is the first harmonic, thus making 4U 1538-52 the
fifth X-ray pulsar with more than one cyclotron line.
