An overview of the results of observations for the transient X-ray pulsar 4U 0115+63, a member of a binary system with a Be star, since its discovery to the present day (~40 years) based on data from more than dozen observatories and instruments is p
resented. A overall light curve and the history of change in the spin frequency of the neutron star over the entire history of its observations, which also includes the results of recent measurements made by the INTEGRAL observatory during the 2004, 2008, and 2011 outbursts, are provided. The sources energy spectra have also been constructed from the INTEGRAL data obtained during the 2011 outburst for a dynamic range of its luminosities (~10^{37} - 7 x 10^{37} erg/s). We show that apart from the fundamental harmonic of the cyclotron absorption line at energy ~11 keV, its four higher harmonics at energies ~24, 35.6, 48.8, and 60.7 keV are detected in the spectrum. We have performed a detailed analysis of the sources spectra in the 4-28 keV energy band based on all of the available RXTE archival data obtained during bright outbursts in 1995-2011. We have confirmed that modifying the sources continuum model can lead to the disappearance of the observed anticorrelation between the energy of the fundamental harmonic of the cyclotron absorption line and the sources luminosity. Thus, the question about the evolution of the cyclotron absorption line energy with the luminosity of the X-ray pulsar 4U 0115+63 remains open and a physically justified radiation model for X-ray pulsars is needed to answer it.
We present the results of a systematic search for outbursts in the narrow positron annihilation line on various time scales (5x10^4 - 10^6 s) based on the SPI/INTEGRAL data obtained from 2003 to 2008. We show that no outbursts were detected with a st
atistical significance higher than ~6 sigma for any of the time scales considered over the entire period of observations. We also show that, given the large number of independent trials, all of the observed spikes could be associated with purely statistical flux fluctuations and, in part, with a small systematic prediction error of the telescopes instrumental background. Based on the exposure achieved in ~6 yr of INTEGRAL operation, we provide conservative upper limits on the rate of outbursts with a given duration and flux in different parts of the sky.
We present here the preliminary results of the study of the fluorescent iron line emission from X-ray pulsars with Be companions. We propose to use properties of this emission to investigate the spatial distribution and physical conditions of the mat
ter around the compact object as well as in the binary system as a whole. Using data of the RXTE observatory the iron line behavior in the transient X-ray pulsar V 0332+53 spectrum was studied during the powerful type II outburst in 2004-2005. Particularly, we investigated a variability of the iron line equivalent width on different time scales (pulse period, orbital period, outburst phase) and searched for its correlation with the continuum flux, spectral parameters, etc.
