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 10^12 G. After 4U0115+63, this makes V0332+53 the second accreting neutron star in which more than two 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. 
K. Pottschmidt (1), I. Kreykenbohm (2,3), J. Wilms (4), W. Coburn (5),   R.E. Rothschild (1), P. Kretschmar (6), V. McBride ...