A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4

TL;DR

This paper reports Suzaku observations of the X-ray pulsar GX 1+4, revealing its spectral properties, emission lines, and the absence of a cyclotron feature, with implications for understanding its accretion and magnetic environment.

Contribution

It introduces a simpler spectral model for GX 1+4, detects a Ni emission line for the first time, and provides detailed spectral analysis including iron and nickel abundances.

Findings

Spectral fitting favors a blackbody plus cutoff power-law model.

No cyclotron resonance scattering feature detected.

First detection of Ni Kα emission line in this source.

Abstract

We present results obtained from a Suzaku observation of the accretion powered X-ray pulsar GX 1+4. Broad-band continuum spectrum of the pulsar was found to be better described by a simple model consisting of a blackbody component and an exponential cutoff power-law than the previously used compTT continuum model. Though the pulse profile had a sharp dip in soft X-rays ($<$10 keV), phase-resolved spectroscopy confirmed that the dimming was not due to increase in photoelectric absorption. Phase-sliced spectral analysis showed the presence of a significant spectral modulation beyond 10 keV except for the dip phase. A search for the presence of cyclotron resonance scattering feature in the Suzaku spectra yielded a negative result. Iron K-shell (K$_\alpha$ and K$_\beta$) emission lines from nearly neutral iron ions ($<$Fe III) were clearly detected in the source spectrum. A significant K$_\alpha$ emission line from almost neutral Ni atoms was detected for the first time in this source. We estimated the iron abundance of $\sim$80 % of the solar value and Ni/Fe abundance ratio of about two times of the solar value. We searched for a iron Ly$_\alpha$ emission line and found a significant improvement in the spectral fitting by inclusion of this line.