RXTE discovery of multiple cyclotron lines during the 2004 December outburst of V0332+53

We present an analysis of the 2 - 150 keV spectrum of the transient X-ray pulsar V0332 + 53 taken with the Rossi X-Ray Timing Explorer ( RXTE) in 2004 December. We report on the detection of three cyclotron resonance features at 27, 51, and 74 keV in the phase-averaged data, corresponding to a polar magnetic field of 2.7 x G. After 4U 0115 + 63, this makes V0332 + 53 the second accreting neutron star in which more than two 12 10 cyclotron lines have been detected; this has now also been confirmed by INTEGRAL. Pulse-phase spectroscopy reveals remarkably little variability of the cyclotron line through the 4.4 s X-ray pulse.