Quasi periodic oscillations in XTE J0111.2-7317, highest frequency among the HMXB pulsar

Abstract

We report here the discovery of Quasi Periodic Oscillations (QPO) in the High Mass X-ray Binary (HMXB) Pulsar XTE J0111.20--7317 during a transient outburst in this source in early 1999. Using observations made with the proportional counter array of the Rossi X-ray Timing Explorer during the second peak and the declining phase of this outburst we have discovered a QPO feature at a frequency of 1.27 Hz. We have also investigated whether the observed QPOs can instead be from the neighbouring bright X-ray pulsar SMC X-1 using a correlation between the pulsed X-ray flux and the average X-ray flux of SMC X-1 over a wide range of its intensity. This is the highest frequency QPO ever detected in any HMXB pulsar. In the absence of a cyclotron absorption feature in the X-ray spectrum, the QPO feature, along with the X-ray flux and pulse period measurement helps us to constrain the magnetic field strength of the neutron star.