Transient X-ray pulsar V 0332+53: Pulse-phase-resolved spectroscopy and the reflection model

Abstract

We present the results of the pulse-phase- and luminosity-resolved spectroscopy of the transient X-ray pulsar V 0332+53, performed for the first time in a wide luminosity range (1-40) × 1037 erg s-1 during a giant outburst observed by the RXTE observatory in 2004 December-2005 February. We characterize the spectra quantitatively and built the detailed 'three-dimensional' picture of spectral variations with pulse phase and throughout the outburst. We show that all spectral parameters are strongly variable with the pulse phase, and the pattern of this variability significantly changes with luminosity directly reflecting the associated changes in the structure of emission regions and their beam patterns. Obtained results are qualitatively discussed in terms of the recently developed reflection model for the formation of cyclotron lines in the spectra of X-ray pulsars.