# Comprehensive Timing and X-ray Spectral Analysis of GX 1+4

## TL;DR

This study combines timing and spectral analysis of GX 1+4 over two decades, revealing long-term torque behavior, spectral correlations, and noise characteristics in an accretion-powered X-ray pulsar.

## Contribution

It provides the first long-term noise analysis extending up to 44 years and links spectral features with flux and pulse phase, enhancing understanding of accretion dynamics.

## Key findings

- Correlation state changes on 100-200 day timescales.
- Flickering noise with a $f^{-1}$ spectrum observed.
- Iron line flux correlates with unabsorbed X-ray flux.

## Abstract

We present analysis of RXTE--PCA observations of GX 1+4 between March 3, 2001 and January 31, 2003 together with the CGRO--BATSE X-ray flux and frequency derivative time series between 1991 and 1999. From the timing analysis of RXTE-PCA observations, we are able to phase connect pulse arrival times of the source within two different time intervals and obtain corresponding timing solutions. Using these pulse arrival times, we contribute to long term pulse frequency history of the source. We look for episodic correlations and anti-correlations between torque and X-ray luminosity using CGRO--BATSE X-ray flux and frequency derivative time series and find that correlation state of GX 1+4 seems to change on $\sim$ 100-200 days long intervals. We estimate torque noise of the source and observe flickering noise ($f^{-1}$). We achieve to measure the longest observed timescale for a noise process among accretion powered X-ray pulsars by extending the noise estimate for a time scale ranging from 31 days to 44 years. Spectral analysis of individual RXTE-PCA observations indicates a significant correlation between iron line flux and unabsorbed X-ray flux. Pulse phase resolved spectra of the source indicate a broadening of iron line complex at the bin corresponding to the pulse minimum.