  We analyze the observations of the transient X-ray pulsar 4U 0115+63 with the
RXTE and INTEGRAL observatories in a wide X-ray (3-100 keV) energy band during
its intense outbursts in 1999 and 2004. The energy of the fundamental harmonic
of the cyclotron resonance absorption line near the maximum of the X-ray flux
from the source (luminosity range 5x10^{37} - 2x10^{38} erg/s) is ~11 keV. When
the pulsar luminosity falls below ~5x10^{37} erg/s, the energy of the
fundamental harmonic is displaced sharply toward the high energies, up to ~16
keV. Under the assumption of a dipole magnetic field configuration, this change
in cyclotron harmonic energy corresponds to a decrease in the height of the
emitting region by ~2 km, while other spectral parameters, in particular, the
cutoff energy, remain essentially constant. At a luminosity ~7x10^{37} erg/s,
four almost equidistant cyclotron line harmonics are clearly seen in the
spectrum. This suggests that either the region where the emission originates is
compact or the emergent spectrum from different (in height) segments of the
accretion column is uniform. We have found significant pulse profile variations
with energy, luminosity, and time. In particular, we show that the profile
variations from pulse to pulse are not reduced to a simple modulation of the
accretion rate specified by external conditions.
