Quasi‐periodic Oscillations in XTE J0111.2−7317: Highest Frequency among the HMXB Pulsars

We report here discovery of Quasi Periodic Oscillations (QPOs) in the HighMass X-ray Binary (HMXB) Pulsar XTE J0111.20-7317 during a transient outburstin this source in December 1998. Using observations made with the proportionalcounter array of the Rossi X-ray Timing Explorer during the second peak and thedeclining phase of this outburst we have discovered a QPO feature at afrequency of 1.27 Hz. We have ruled out the possibility that the observed QPOscan instead be from the neighbouring bright X-ray pulsar SMC X-1. This is thehighest frequency QPO feature ever detected in any HMXB pulsar. In the absenceof a cyclotron absorption feature in the X-ray spectrum, the QPO feature, alongwith the pulse period and X-ray flux measurement measurement helps us toconstrain the magnetic field strength of the neutron star.Comment: Accepted for publication in The Astrophysical Journa