Phase-resolved spectral analysis of 4U 1901+03 during its outburst

TL;DR

This study conducts a phase-resolved spectral analysis of the high mass X-ray binary 4U 1901+03 during its 2003 outburst, revealing phase-dependent spectral features and insights into the origin of Fe emission.

Contribution

It provides the first detailed phase-resolved energy spectrum analysis of 4U 1901+03, highlighting phase-dependent spectral variations and the origin of Fe emission.

Findings

Both continuum and pulse spectra are phase-dependent.

Optical depth is generally larger in pulse spectra.

Fe Ka emission line is absent in pulse spectrum, indicating disk origin.

Abstract

The high mass X-ray binary 4U 1901+03 was reported to have the pulse profile evolving with the X-ray luminosity and energy during its outburst in February-July 2003: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by Rossi X-ray Timing Explorer (RXTE). We find that, both the continuum and the pulse spectra are phase dependent. The optical depth derived from the pulse spectrum is in general larger than that from the continuum. Fe Ka emission line is only detected in the spectrum of the continuum and is missing in the pulse spectrum. This suggests an origin of Fe emission from the accretion disk but not the surface of the neutron star.