ART-P/Granat observations of the X-ray pulsar 4U0115+634 during the outburst in February 1990

Observations of the transient X-ray pulsar 4U0115+634 with the ART-P telesc ope aboard the Granat Observatory during the outburst in February 1990 art: presented. The source exhibited a strong, regular and irregular variabilit y, including X-ray bursts of duration 300-500 s. Two absorption features we re detected in the source's photon spectrum at similar to 12 and similar to 22 keV, which were interpreted as the lines of resonance scattering of its emission at the first and second cyclotron harmonics. The magnetic-field s trength B on the neutron-star surface that corresponds to these lines is si milar to 1.3 x 10(12) G. The ratio of the line energies slightly differs fr om the harmonic ratio 1 : 2. Moreover, this ratio and the line energies the mselves vary appreciably with phase on a time scale of one pulsation period . The dependence of other spectral parameters for 4U0115+634 on pulse phase is investigated. (C) 2000 MAIK "Nauka/Interperiodica".