Disk reflection signatures in the spectrum of the bright Z-source GX 340+0

TL;DR

This study analyzes XMM-Newton data of GX 340+0, revealing a relativistically broadened iron emission line from the accretion disk that remains stable despite changes in the source's continuum emission.

Contribution

It provides the first detailed spectral analysis of the relativistic iron line in GX 340+0, constraining disk geometry and emission properties during different source states.

Findings

Broad asymmetric Fe K alpha line detected, consistent with relativistic reflection.

Inner disk radius estimated at approximately 13 gravitational radii.

Source inclination constrained at 35 degrees.

Abstract

We present the preliminary results of a 50 ks long XMM-Newton observation of the bright Z-source GX 340+0. In this Letter we focus on the study of a broad asymmetric emission line in the Fe K alpha energy band, whose shape is clearly resolved and compatible with a relativistically smeared profile arising from reflection on a hot accretion disk extending close to the central accreting neutron star. By combining temporal and spectral analysis, we are able to follow the evolution of the source along its Horizontal Branch. However, despite a significant change in the continuum emission and luminosity, the line profile does not show any strong correlated variation. This broad line is produced by recombination of highly ionized iron (Fe XXV) at an inferred inner radius close to 13 gravitational radii while the fit requires a high value for the outer disk radius. The inclination of the source is extremely well constrained at 35 deg, while the emissivity index is -2.50.