QUASI-PERIODIC OSCILLATIONS DISCOVERED IN THE NEW X-RAY PULSAR XTE J1858+034

We report the discovery of low frequency quasiperiodic oscillations ce ntered at 0.11 Hz in the newly discovered 221 a X-ray pulsar XTE J1858 +034. Among about 30 known transient X-ray pulsars this is the sixth s ource in which QPOs have been observed. If the QPOs are produced becau se of inhomogeneities in the accretion disk at the magnetospheric boun dary, the low frequency of the QPOs indicate a large magnetosphere for this pulsar. Both the Keplerian frequency model and the beat frequenc y model are applicable for production of QPOs in this source. The QPOs and regular pulsations are found to be stronger at higher energy whic h favours the beat frequency model. The magnetic field of the pulsar i s calculated as a function of its distance. The energy spectrum is fou nd to be very hard, consisting of two components, a cut-off power law and an iron fluorescence line.