Active galaxy 4U 1344-60: did the relativistic line disappear?

TL;DR

This study compares X-ray observations of active galaxy 4U 1344-60 from XMM-Newton and Suzaku, revealing the disappearance of relativistic reflection features and a change in the iron line profile, suggesting transient inner accretion phenomena.

Contribution

It provides the first detailed comparison of Suzaku and XMM-Newton spectra for 4U 1344-60, showing the transient nature of relativistic reflection features in this galaxy.

Findings

Relativistic reflection features are absent in Suzaku data.

The iron line is narrow and lacks relativistic broadening in Suzaku spectra.

A red-shifted iron line was observed in XMM-Newton data, possibly transient.

Abstract

X-ray bright active galactic nuclei represent a unique astrophysical laboratory for studying accretion physics around super-massive black holes. 4U 1344-60 is a bright Seyfert galaxy which revealed relativistic reflection features in the archival XMM-Newton observation. We present the spectroscopic results of new data obtained with the Suzaku satellite and compare them with the previous XMM-Newton observation. The X-ray continuum of 4U 1344-60 can be well described by a power-law component with the photon index ~ 1.7 modified by a fully and a partially covering local absorbers. We measured a substantial decrease of the fraction of the partially absorbed radiation from around 45% in the XMM-Newton observation to less than 10% in the Suzaku observation while the power-law slope remains constant within uncertainties. The iron line in the Suzaku spectrum is relatively narrow, $\sigma=(0.08 \pm 0.02)$ keV, without any suggestion for relativistic broadening. Regarding this, we interpret the iron line in the archival XMM-Newton spectrum as a narrow line of the same width plus an additional red-shifted emission around 6.1 keV. No evidence of the relativistic reflection is present in the Suzaku spectra. The detected red-shifted iron line during the XMM-Newton observation could be a temporary feature either due to locally enhanced emission or decreased ionisation in the innermost accretion flow.