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Optical and X-ray variability of two Small Magellanic Cloud X-ray binary pulsars - SXP46.6 and SXP6.85

Optical and X-ray variability of two Small Magellanic Cloud X-ray binary pulsars - SXP46.6 and SXP6.85
Optical and X-ray variability of two Small Magellanic Cloud X-ray binary pulsars - SXP46.6 and SXP6.85
We present long-term optical and RXTE data of two X-ray binary pulsars in the Small Magellanic Cloud, SXP46.6 and SXP6.85. The optical light curves of both sources show substantial (?0.5-0.8 mag) changes over the time-span of the observations. While the optical data for SXP6.85 do not reveal any periodic behaviour, by detrending the optical measurements for SXP46.6 we find an orbital period of ?137 d, consistent with results from the X-ray data. The detection of Type I X-ray outbursts from SXP46.6, combined with the fact that we also see optical outbursts at these times, implies that SXP46.6 is a high orbital eccentricity system. Using contemporaneous optical spectra of SXP46.6, we find that the equivalent width of the Ha emission line changes over time indicating that the size of the circumstellar disc varies. By studying the history of the colour variations for SXP6.85, we find that the source gets redder as it brightens which can also be attributed to changes in the circumstellar disc. We do not find any correlation between the X-ray and optical data for SXP6.85. The results for SXP6.85 suggest that it is a low-eccentricity binary and that the optical modulations are due to the Be phenomenon.
stars: emission-line, be, magellanic clouds, x-rays: binaries
0035-8711
821-826
McGowan, K.E.
1d9a32e0-414b-462b-ab42-9901e4aeb2f3
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Schurch, M.P.
46719dcd-eeee-4190-87de-f6afe7fd6063
Corbet, R.H.
112be2fb-0730-466d-9584-79d8e9ae453a
Galache, J.L.
f4b15a28-e3a7-49bb-9000-4e75df9d93ad
Udalski, A.
a7d3b194-1531-47cd-a634-abe3b8b067b0
McGowan, K.E.
1d9a32e0-414b-462b-ab42-9901e4aeb2f3
Coe, M.J.
04dfb23b-1456-46a3-9242-5cee983471d5
Schurch, M.P.
46719dcd-eeee-4190-87de-f6afe7fd6063
Corbet, R.H.
112be2fb-0730-466d-9584-79d8e9ae453a
Galache, J.L.
f4b15a28-e3a7-49bb-9000-4e75df9d93ad
Udalski, A.
a7d3b194-1531-47cd-a634-abe3b8b067b0

McGowan, K.E., Coe, M.J., Schurch, M.P., Corbet, R.H., Galache, J.L. and Udalski, A. (2008) Optical and X-ray variability of two Small Magellanic Cloud X-ray binary pulsars - SXP46.6 and SXP6.85. Monthly Notices of the Royal Astronomical Society, 384 (2), 821-826. (doi:10.1111/j.1365-2966.2007.12762.x).

Record type: Article

Abstract

We present long-term optical and RXTE data of two X-ray binary pulsars in the Small Magellanic Cloud, SXP46.6 and SXP6.85. The optical light curves of both sources show substantial (?0.5-0.8 mag) changes over the time-span of the observations. While the optical data for SXP6.85 do not reveal any periodic behaviour, by detrending the optical measurements for SXP46.6 we find an orbital period of ?137 d, consistent with results from the X-ray data. The detection of Type I X-ray outbursts from SXP46.6, combined with the fact that we also see optical outbursts at these times, implies that SXP46.6 is a high orbital eccentricity system. Using contemporaneous optical spectra of SXP46.6, we find that the equivalent width of the Ha emission line changes over time indicating that the size of the circumstellar disc varies. By studying the history of the colour variations for SXP6.85, we find that the source gets redder as it brightens which can also be attributed to changes in the circumstellar disc. We do not find any correlation between the X-ray and optical data for SXP6.85. The results for SXP6.85 suggest that it is a low-eccentricity binary and that the optical modulations are due to the Be phenomenon.

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More information

Published date: 21 January 2008
Keywords: stars: emission-line, be, magellanic clouds, x-rays: binaries
Organisations: University of Southampton

Identifiers

Local EPrints ID: 143579
URI: http://eprints.soton.ac.uk/id/eprint/143579
ISSN: 0035-8711
PURE UUID: 3c44984f-f597-4a69-8021-d63a7afc1f40
ORCID for M.J. Coe: ORCID iD orcid.org/0000-0002-0763-8547

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Date deposited: 12 Apr 2010 12:04
Last modified: 18 Feb 2021 16:34

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Contributors

Author: K.E. McGowan
Author: M.J. Coe ORCID iD
Author: M.P. Schurch
Author: R.H. Corbet
Author: J.L. Galache
Author: A. Udalski

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