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SXP 7.92: a recently rediscovered Be/X-ray binary in the Small Magellanic Cloud, viewed edge on

SXP 7.92: a recently rediscovered Be/X-ray binary in the Small Magellanic Cloud, viewed edge on
SXP 7.92: a recently rediscovered Be/X-ray binary in the Small Magellanic Cloud, viewed edge on
We present a detailed optical and X-ray study of the 2013 outburst of the Small Magellanic Cloud Be/X-ray binary SXP 7.92, as well as an overview of the last 18 years of observations from OGLE (Optical Gravitational Lensing Experiment), RXTE, Chandra and XMM-Newton. We revise the position of this source to RA(J2000) = 00:57:58.4, Dec(J2000) = −72:22:29.5 with a 1σ uncertainty of 1.5 arcsec, correcting the previously reported position by Coe et al. by more than 20 arcmin. We identify and spectrally classify the correct counterpart as a B1Ve star. The optical spectrum is distinguished by an uncharacteristically deep narrow Balmer series, with the Hα line in particular having a distinctive shell profile, i.e. a deep absorption core embedded in an emission line. We interpret this as evidence that we are viewing the system edge on and are seeing self-obscuration of the circumstellar disc. We derive an optical period for the system of 40.0 ± 0.3 d, which we interpret as the orbital period, and present several mechanisms to describe the X-ray/optical behaviour in the recent outburst, in particular the ‘flares'and ‘dips’ seen in the optical light curve, including a transient accretion disc and an elongated precessing disc.
0035-8711
4659-4671
Bartlett, E.S.
e7d65e6a-d46d-4e49-81af-cf7a62fdb6e1
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Israel, G.
a04ed06a-d10a-4d1a-b8be-700442435fd1
Clark, J.S.
e66e2e8a-0fbc-4c4e-92c8-3bd0ed2e1c38
Esposito, P.
811d6f7c-9079-4a3e-b70d-08c950d5687f
D'Elia, V.
b500ae34-300f-4627-9b6d-da6551d343f3
Udalski, A.
a7d3b194-1531-47cd-a634-abe3b8b067b0
Bartlett, E.S.
e7d65e6a-d46d-4e49-81af-cf7a62fdb6e1
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Israel, G.
a04ed06a-d10a-4d1a-b8be-700442435fd1
Clark, J.S.
e66e2e8a-0fbc-4c4e-92c8-3bd0ed2e1c38
Esposito, P.
811d6f7c-9079-4a3e-b70d-08c950d5687f
D'Elia, V.
b500ae34-300f-4627-9b6d-da6551d343f3
Udalski, A.
a7d3b194-1531-47cd-a634-abe3b8b067b0

Bartlett, E.S., Coe, M.J., Israel, G., Clark, J.S., Esposito, P., D'Elia, V. and Udalski, A. (2017) SXP 7.92: a recently rediscovered Be/X-ray binary in the Small Magellanic Cloud, viewed edge on. Monthly Notices of the Royal Astronomical Society, 466 (4), 4659-4671. (doi:10.1093/mnras/stx032).

Record type: Article

Abstract

We present a detailed optical and X-ray study of the 2013 outburst of the Small Magellanic Cloud Be/X-ray binary SXP 7.92, as well as an overview of the last 18 years of observations from OGLE (Optical Gravitational Lensing Experiment), RXTE, Chandra and XMM-Newton. We revise the position of this source to RA(J2000) = 00:57:58.4, Dec(J2000) = −72:22:29.5 with a 1σ uncertainty of 1.5 arcsec, correcting the previously reported position by Coe et al. by more than 20 arcmin. We identify and spectrally classify the correct counterpart as a B1Ve star. The optical spectrum is distinguished by an uncharacteristically deep narrow Balmer series, with the Hα line in particular having a distinctive shell profile, i.e. a deep absorption core embedded in an emission line. We interpret this as evidence that we are viewing the system edge on and are seeing self-obscuration of the circumstellar disc. We derive an optical period for the system of 40.0 ± 0.3 d, which we interpret as the orbital period, and present several mechanisms to describe the X-ray/optical behaviour in the recent outburst, in particular the ‘flares'and ‘dips’ seen in the optical light curve, including a transient accretion disc and an elongated precessing disc.

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More information

Accepted/In Press date: 5 January 2017
e-pub ahead of print date: 11 January 2017
Published date: 1 May 2017

Identifiers

Local EPrints ID: 420418
URI: https://eprints.soton.ac.uk/id/eprint/420418
ISSN: 0035-8711
PURE UUID: f19c7267-fcf6-407f-a6d9-e36ac8f13d75
ORCID for M.J. Coe: ORCID iD orcid.org/0000-0002-0763-8547

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Date deposited: 04 May 2018 16:31
Last modified: 14 Mar 2019 01:56

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Contributors

Author: E.S. Bartlett
Author: M.J. Coe ORCID iD
Author: G. Israel
Author: J.S. Clark
Author: P. Esposito
Author: V. D'Elia
Author: A. Udalski

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