On the Fe K absorption - accretion state connection in the Galactic Centre neutron star X-ray binary AX J1745.6-2901
Date Issued
2015
Author(s)
•
Bianchi, S.
•
Muñoz-Darias, T.
•
De Marco, B.
•
Dwelly, T.
•
Fender, R. P.
•
Nandra, K.
•
Rea, N.
•
Mori, K.
•
Haggard, D.
•
Heinke, C. O.
•
Degenaar, N.
•
Aramaki, T.
•
Clavel, M.
•
Goldwurm, A.
•
Hailey, C. J.
•
•
Morris, M. R.
•
Rushton, A.
•
Terrier, R.
Description
The authors wish to thank Jan-Uwe Ness, Ignacio de la Calle and the rest of the XMM–Newton scheduling team for the enormous support that made the new XMM–Newton observations possible. GP and TMD acknowledge support via an EU Marie Curie Intra-European fellowship under contract no. FP-PEOPLE-2012-IEF-331095 and FP-PEOPLE-2011-IEF-301355, respectively. The GC XMM–Newton monitoring project is partially supported by the Bundesministerium für Wirtschaft und Technologie/Deutsches Zentrum für Luft- und Raumfahrt (BMWI/DLR, FKZ 50 OR 1408) and the Max Planck Society. This project was funded in part by European Research Council Advanced Grant 267697 ‘4π sky: Extreme Astrophysics with Revolutionary Radio Telescopes’. DH acknowledges support from Chandra X-ray Observatory (CXO) Award Number GO3-14121X, operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060, and also by NASA Swift grant NNX14AC30G. CH is supported by an NSERC Discovery Grant, and an Ingenuity New Faculty Award. ND is supported by NASA through Hubble Postdoctoral Fellowship grant number HST-HF-51287.01-A from the Space Telescope Science Institute. The scientific results reported in this article are based on observations obtained with XMM–Newton , Swift and NuSTAR .
Abstract
AX J1745.6-2901 is a high-inclination (eclipsing) neutron star low-mass X-ray binary (LMXB) located less than ~ 1.5 arcmin from Sgr A⋆. Ongoing monitoring campaigns have targeted Sgr A⋆ frequently and these observations also cover AX J1745.6-2901. We present here an X-ray analysis of AX J1745.6-2901 using a large data set of 38 XMM-Newton observations, including 11 which caught AX J1745.6-2901 in outburst. Fe K absorption is clearly seen when AX J1745.6-2901 is in the soft state, but disappears during the hard state. The variability of these absorption features does not appear to be due to changes in the ionizing continuum. The small Kα/Kβ ratio of the equivalent widths of the Fe XXV and Fe XXVI lines suggests that the column densities and turbulent velocities of the absorbing ionized plasma are in excess of N_H ≃ 10^23 cm^-2 and v_turb ≳ 500 km/s. These findings strongly support a connection between the wind (Fe K absorber) and the accretion state of the binary. These results reveal strong similarities between AX J1745.6-2901 and the eclipsing neutron star LMXB, EXO 0748-676, as well as with high-inclination black hole binaries, where winds (traced by the same Fe K absorption features) are observed only during the accretion-disc-dominated soft states, and disappear during the hard states characterized by jet emission.
Volume
446
Issue
2
Start page
1536
Issn Identifier
0035-8711
Ads BibCode
2015MNRAS.446.1536P
Rights
open.access
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