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Swift monitoring of supergiant fast X-ray transients: The out-of-outburst behaviour and the flares from IGR J17544-2916 and XTE J1739-302

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posted on 09.10.2019, 15:28 by L Sidoli, P Romano, G Cusumano, V Mangano, S Vercellone, A Paizis, A Pellizzoni, JA Kennea, DN Burrows, HA Krimm, N Gehrels, C Guidorzi, PA Evans
Supergiant Fast X-ray Transients (SFXTs) are a sub-class of High Mass X-ray Binaries (HMXBs) associated with OB supergiant companions and displaying transient X-ray activity. This behaviour is quite surprising since HMXBs hosting supergiants were known to be persistent sources, until the INTEGRAL discoveries obtained by means of the monitoring of the Galactic plane. We have been performing a monitoring campaign with Swift of four SFXTs with the main aim of characterizing both the long-term behaviour of these transients and the properties during bright outbursts. Here we discuss the properties of the X-ray emission observed outside the outbursts as well as the flares observed from two SFXTs: IGR J17544-2916 and XTE J1739-302. Contrarily to what previously thought, Swift allowed us to discover that SFXTs spend most of the time in accretion at a low level, even outside the bright outbursts, with an accretion luminosity of 1033-1034 erg s-1, and that the quiescent level ∼1032 erg s-1, is a much rarer state.

Funding

ASI I/023/05/0, I/088/06/0, and I/008/07/0, at PSU by NASA contract NAS5-00136.

History

Citation

Proceedings of Science, 2008, Vol. 067

Author affiliation

/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy

Source

7th INTEGRAL Workshop (Integral08), Copenhagan, Denmark

Version

VoR (Version of Record)

Published in

Proceedings of Science

Publisher

Sissa Medialab srl Partita IVA

eissn

1824-8039

Acceptance date

01/09/2008

Copyright date

2009

Available date

09/10/2019

Publisher version

https://pos.sissa.it/067/084/

Language

en

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