Investigation of quasi periodic signals of X-Ray bursts from neutron star AXP 1E2259+586 using Fourier analysis techniques

Abstract

Investigation of Quasi Periodic Oscillations (QPOs) in the spacecraft instrument signals provides significant insights towards understanding the physical processes that are taking place in the emissions of X-rays. The QPOs are the frequency oscillations which give us more and detailed information about the science of stars. Since astronomy is an observational and not experimental science; the physics of stars cannot be studied by traditional methods of changing variables. In this paper, we present how the Fourier analysis and its computational algorithm of Fast Fourier Transform (FFT) can be applied towards detection of the QPOs by generating the power-frequency curves of various x-ray bursts.

To undertake this study, the science of High Energy Astrophysics (HEA) has been applied in parallel with exploration of the digital observational data from Rossi X-ray Timing Explorer (RXTE) spacecraft databases which are freely made available from NASA & ESA electronic archives. The sample data used are those of the neutron star Anomalous X-Ray Pulsar (AXP) 1E2259+586. The study involved intense computer programming using tools such as UBUNTU 10.04 OS, MATLAB 2010a UBUNTU compatible version for data visualization, HEASOFT-6.10 package with FTools and IDL software for processing of the science events.

A timing analysis of QPOs has been accomplished through applying computational technique of FFT algorithm.

The study reveals that FFT is a strong mathematical tool in finding QPOs of the X-ray bursts. The FFT applied on the light curve with the highest time resolution can manage to remove the background noise and detect a QPO’s signal. To detect a QPO event, the FFT must show the high power peaks above f = 100 Hz or through the 3 sigma level of normalized FFT plots which indicates a QPO when its power level is of high value. The statistical significance of QPOs can be established by fitting with a Gaussian function to determine the width and central frequency and to assess the Fourier Analysis method using a probabilistic approach of the Monte Carlo Simulation (MCS) by running random number of simulations in MATLAB computing language.

The main contribution of this work is to demonstrate the strength of Fourier analysis in Digital Signal Processing (DSP) and show the extent on which it can be applied in analyzing spacecraft data. The software and technical challenges have been raised to promote support for researchers in developing countries.

Keywords: Fourier Analysis, FFT, QPO,X-Ray:burst,Star: neutron, Pulsar: AXP 1E2259+586