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

¹ European Space Astronomy Centre of ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
e-mail: jsvoboda@sciops.esa.int
² Università degli Studi Roma Tre, via dellaVasca Navale 84, 00146 Roma, Italy
³ Osservatorio Astronomico di Roma (INAF), via Frascati 33, 00040 Monteporzio Catone (Roma), Italy
⁴ Astronomical Institute, Academy of Sciences, Boční II 1401, 14131 Prague, Czech Republic

Received: 27 April 2012
Accepted: 28 August 2012

Abstract

Context. X-ray bright active galactic nuclei represent a unique astrophysical laboratory for studying accretion physics around super-massive black holes.

Aims. 4U 1344-60 is a bright Seyfert galaxy which revealed relativistic reflection features in the archival XMM-Newton observation.

Methods. We present the spectroscopic results of new data obtained with the Suzaku satellite and compare them with the previous XMM-Newton observation.

Results. 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, σ = (0.08 ± 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.

Conclusions. 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.