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INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient

INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient
INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient
We report on combined INTEGRAL and XMM–Newton observations of the supergiant fast X-ray transient (SFXT) IGR J16418-4532. The observations targeted the X-ray eclipse region of IGR J16418-4532's orbit with continuous INTEGRAL observations across ~25 per cent of orbital phase and two quasi-simultaneous XMM–Newton observations of length 20 and 14 ks, occurring during and just after the eclipse, respectively. An enhanced INTEGRAL emission history is provided with 19 previously unreported outbursts identified in the archival 18–60 keV data set. The XMM–Newton eclipse observation showed prominent Fe emission and a flux of 2.8 × 10-13 erg cm-2 s-1 (0.5–10 keV). Through the comparison of the detected eclipse and post-eclipse flux, the supergiant mass-loss rate through the stellar wind was determined as w = 2.3–3.8 × 10-7 M yr-1. The post-eclipse XMM–Newton observation showed a dynamic flux evolution with signatures of the X-ray pulsation, a period of flaring activity, structured nH variations and the first ever detection of an X-ray intensity dip, or ‘off-state’, in a pulsating SFXT. Consideration is given to the origin of the X-ray dip, and we conclude that the most applicable of the current theories of X-ray dip generation is that of a transition between Compton-cooling-dominated and radiative-cooling-dominated subsonic accretion regimes within the ‘quasi-spherical’ model of wind accretion. Under this interpretation, which requires additional confirmation, the neutron star in IGR J16418-4532 possesses a magnetic field of ~1014 G, providing tentative observational evidence of a highly magnetized neutron star in a SFXT for the first time. The implications of these results on the nature of IGR J16418-4532 itself and the wider SFXT class are discussed.
accretion, accretion discs, stars: winds, outflows, X-rays: binaries, X-rays: individual: IGR J16418?4532
0035-8711
528-542
Drave, S.P.
58e686f1-8ddf-4e6c-ae26-8a124d4930ae
Bird, A.J.
045ee141-4720-46fd-a412-5aa848a91b32
Sidoli, L.
2207422d-1a4d-448c-8c0b-8f0c2bf78a18
Sguera, V.
371bb568-7e56-496e-a624-dba6de79d9e1
McBride, V. A.
f3eeb4b2-bdb1-4817-af63-6684cdf28e10
Hill, A. B.
b1007941-b5b1-47cd-8476-7c6b9c57f347
Bazzano, A.
8eef0c6e-1a5f-4bcd-a034-9a5c3b29104d
Goossens, M. E.
235aceb1-f527-4f2a-8f5e-8b680936c062
Drave, S.P.
58e686f1-8ddf-4e6c-ae26-8a124d4930ae
Bird, A.J.
045ee141-4720-46fd-a412-5aa848a91b32
Sidoli, L.
2207422d-1a4d-448c-8c0b-8f0c2bf78a18
Sguera, V.
371bb568-7e56-496e-a624-dba6de79d9e1
McBride, V. A.
f3eeb4b2-bdb1-4817-af63-6684cdf28e10
Hill, A. B.
b1007941-b5b1-47cd-8476-7c6b9c57f347
Bazzano, A.
8eef0c6e-1a5f-4bcd-a034-9a5c3b29104d
Goossens, M. E.
235aceb1-f527-4f2a-8f5e-8b680936c062

Drave, S.P., Bird, A.J., Sidoli, L., Sguera, V., McBride, V. A., Hill, A. B., Bazzano, A. and Goossens, M. E. (2013) INTEGRAL and XMM-Newton observations of IGR J16418-4532: evidence of accretion regime transitions in a supergiant fast X-ray transient. Monthly Notices of the Royal Astronomical Society, 433 (1), 528-542. (doi:10.1093/mnras/stt754).

Record type: Article

Abstract

We report on combined INTEGRAL and XMM–Newton observations of the supergiant fast X-ray transient (SFXT) IGR J16418-4532. The observations targeted the X-ray eclipse region of IGR J16418-4532's orbit with continuous INTEGRAL observations across ~25 per cent of orbital phase and two quasi-simultaneous XMM–Newton observations of length 20 and 14 ks, occurring during and just after the eclipse, respectively. An enhanced INTEGRAL emission history is provided with 19 previously unreported outbursts identified in the archival 18–60 keV data set. The XMM–Newton eclipse observation showed prominent Fe emission and a flux of 2.8 × 10-13 erg cm-2 s-1 (0.5–10 keV). Through the comparison of the detected eclipse and post-eclipse flux, the supergiant mass-loss rate through the stellar wind was determined as w = 2.3–3.8 × 10-7 M yr-1. The post-eclipse XMM–Newton observation showed a dynamic flux evolution with signatures of the X-ray pulsation, a period of flaring activity, structured nH variations and the first ever detection of an X-ray intensity dip, or ‘off-state’, in a pulsating SFXT. Consideration is given to the origin of the X-ray dip, and we conclude that the most applicable of the current theories of X-ray dip generation is that of a transition between Compton-cooling-dominated and radiative-cooling-dominated subsonic accretion regimes within the ‘quasi-spherical’ model of wind accretion. Under this interpretation, which requires additional confirmation, the neutron star in IGR J16418-4532 possesses a magnetic field of ~1014 G, providing tentative observational evidence of a highly magnetized neutron star in a SFXT for the first time. The implications of these results on the nature of IGR J16418-4532 itself and the wider SFXT class are discussed.

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e-pub ahead of print date: 30 May 2013
Published date: 21 July 2013
Keywords: accretion, accretion discs, stars: winds, outflows, X-rays: binaries, X-rays: individual: IGR J16418?4532
Organisations: Physics & Astronomy

Identifiers

Local EPrints ID: 369395
URI: http://eprints.soton.ac.uk/id/eprint/369395
ISSN: 0035-8711
PURE UUID: 11e2fe3f-8621-46a1-8d17-e1c3f0de39ef
ORCID for A.J. Bird: ORCID iD orcid.org/0000-0002-6888-8937
ORCID for A. B. Hill: ORCID iD orcid.org/0000-0003-3470-4834

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Date deposited: 25 Sep 2014 11:26
Last modified: 21 Nov 2021 02:54

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Contributors

Author: S.P. Drave
Author: A.J. Bird ORCID iD
Author: L. Sidoli
Author: V. Sguera
Author: V. A. McBride
Author: A. B. Hill ORCID iD
Author: A. Bazzano
Author: M. E. Goossens

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