RXTE/PCA Observations: "Variable QPOs for Transient Be/X-Ray Binary Pulsar

We present results from study of timing properties and report the detection of variable quasi-periodic oscillations (QPO) between 0.36-0.74 Hz in the transient Be/X-ray binary pulsar EXO~2030+375 using RXTE/PCA observations. The observations used in the present work were carried out during the X-ray outbursts in 2006 (March-May-June-August-September-October-November) and 2011 (January-February-April- May-June-July-August-September-November-December). The 0.36-0.74 Hz variable QPOs in EXO~2030+375 were detected in seven Rossi Explorer Timing Experiment (RXTE) Proportional Counter Array (PCA) observations during the rising and declining phase of its giant outburst 2006 and normal outburst of 2011. However, these QPOs were never detected during other outbursts of the pulsar. Though QPO of 0.2 Hz were reported earlier in the pulsar, the 0.36-0.74 Hz variable QPOs were detected for the first time in this pulsar. The results of our analysis of RXTE data during two outbursts of the pulsar are presented in the paper.