Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud
Maggi P, Haberl F, Sturm R, Pietsch W, Rau A, Greiner J, Udalski A, Sasaki M (2013)
Publication Status: Published
Publication Type: Journal article
Publication year: 2013
Journal
Publisher: EDP SCIENCES S A
Book Volume: 554
DOI: 10.1051/0004-6361/201321238
Abstract
Aims: We report the discovery of LXP 169, a new high-mass X-ray binary
in the Large Magellanic Cloud. The optical counterpart has been
identified and appears to exhibit an eclipsing light curve. We performed
follow-up observations to clarify the eclipsing nature of the system.
Methods: Energy spectra and time series were extracted from two
XMM-Newton observations to search for pulsations, characterise the
spectrum, and measure spectral and timing changes. Long-term X-ray
variability was studied using archival ROSAT data. The XMM-Newton
positions were used to identify the optical counterpart. We obtained
ultraviolet to near-infrared photometry to characterise the companion,
along with its 4000 d I-band light curve and colour-magnitude
variability. We observed LXP 169 with Swift at two predicted eclipse
times.
Results: We found a spin period of 168.8 s that did not
change between two XMM-Newton observations. The X-ray spectrum, well
characterised by a power law, was harder when the source was brighter.
The X-ray flux of LXP 169 is found to be variable by a factor of at
least 10. The counterpart is highly variable on short and long
timescales, and its photometry is that of an early-type star with an
ouflowing circumstellar disc producing a near-infrared excess. This
classifies the source as a Be/X-ray binary pulsar. We observe a transit
in the ultraviolet, thereby confirming that the companion star itself is
eclipsed. We give an ephemeris for the transit of MJD 56 203.877-0.197+0.934
+ N × (24.329±0.008). We propose and discuss the scenario where the
matter captured from the companion's equatorial disc creates an extended
region of high density around the neutron star, which partially
eclipses the companion as the neutron star transits in front of it.
Conclusions: This is most likely the first time the compact object in
an X-ray binary is observed to eclipse its companion star. LXP 169 would
be the first eclipsing Be/X-ray binary, and a wealth of important
information might be gained from additional observations, such as a
measure of the possible Be disc/orbital plane misalignment, or the mass
of the neutron star.
Authors with CRIS profile
Involved external institutions
Max-Planck-Institut für extraterrestrische Physik (MPE) / Max Planck Institute for Extraterrestrial Physics
Germany (DE)
Eberhard Karls Universität Tübingen
Germany (DE)
University of Warsaw / Uniwersytet Warszawski
Poland (PL)
Germany (DE)
Eberhard Karls Universität Tübingen
Germany (DE)
University of Warsaw / Uniwersytet Warszawski
Poland (PL)
How to cite
APA:
Maggi, P., Haberl, F., Sturm, R., Pietsch, W., Rau, A., Greiner, J.,... Sasaki, M. (2013). Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud. Astronomy & Astrophysics, 554. https://doi.org/10.1051/0004-6361/201321238
MLA:
Maggi, P., et al. "Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud." Astronomy & Astrophysics 554 (2013).
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