Search for photon bubble oscillations in V0332+53

TL;DR

This study searched for fast photon bubble oscillations in the bright pulsar V0332+53 using RXTE data, but found no such oscillations within the 200-1500 Hz frequency range, after accounting for instrumental noise effects.

Contribution

The paper demonstrates the importance of accounting for instrumental noise in high-frequency oscillation searches and provides an upper limit on oscillation amplitude in V0332+53.

Findings

No quasi-periodic oscillations detected in 200-1500 Hz range.

Instrumental noise caused by cross-talk affects soft and hard sub-bands.

Upper limit of 0.5% on oscillation amplitude in the source.

Abstract

We report results of our search for fast oscillations in lightcurve of one of the brightest accretion powered pulsars on the sky V0332+53 with the help of data of the PCA spectrometer of the RXTE observatory. In course of this search we have carefully explored complications appearing if one uses only sub-bands of the total bandpass of the PCA spectrometer. We show that lightcurves collected in the soft sub-band of the PCA spectrometer contains an additional instrumental noise, lightcurves of harder sub-bands lack some fraction of the anticipated Poisson noise. We show that this noise is caused by a cross-talk of energy bands, which lasts up to ~200usec. One hypothesis is that these effects are caused by temporarily drop of the PCA detector gain after any occurred event due to slowly moving ions in the detector volume. In order to avoid this effect we searched for fast oscillations in flux of V0332+53 only in the total bandpass of the PCA spectrometer 2-60 keV. We have not detected any quasi-periodic oscillations in lightcurve of the source with an upper limit at the level of 0.5% in the Fourier frequency range 200-1500 Hz.