SXP 5.05 = IGR J00569-7226 : using X-rays to explore the structure of a Be stars circumstellar disk

M. J. Coe(1), E. S. Bartlett(2), A.J. Bird(1), F. Haberl(3), J. A. Kennea(4), V.A. McBride(2;5)
L.J. Townsend(2) & A. Udalski(6)

1 Physics and Astronomy, University of Southampton, SO17 1BJ, UK.
2 Astronomy, Gravity and Cosmology Centre, Department of Astronomy, University of Cape Town, Rondebosch, 7701, South Africa.
3 Max-Planck-Institut f ¨ur extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
4 Department of Astronomy and Astrophysics, The Pennsylvania State University, University Park, PA 16802, USA.
5 South African Astronomical Observatory, PO Box 9, Observatory, 7935, South Africa.
6 Warsaw University Observatory, Aleje Ujazdowskie 4, 00-478 Warsaw, Poland

On MJD 56590-1 (2013 Oct 25-26) observations of the Magellanic Clouds by the
INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observatory discovered
a previously-unreported bright, flaring X-ray source. This source was initially
given the identification IGR J00569-7226. Subsequent multi-wavelength observations
identified the system as new Be/X-ray binary system in the Small Magellanic Cloud.
Follow-up X-ray observations by Swift and XMM-Newton revealed an X-ray pulse
period of 5.05s and that the system underwent regular occulation/eclipse behaviour
every 17d. This is the first reported eclipsing Be/X-ray binary system in the SMC,
and only the second such system known to date. Furthermore, the nature of the occultation
makes it possible to use the neutron star to “X-ray” the circumstellar disk,
thereby, for the first time, revealing direct observational evidence for its size and
clumpy structure. Swift timing measurements allowed for the binary solution to be
calculated from the Doppler shifted X-ray pulsations. This solution suggests this is
a low eccentricity binary relative to others measured in the SMC. Finally it is interesting
to note that the mass determined from this dynamical method for the Be star
( 13 solar masses) is significantly different from that inferred from the spectroscopic classification
of B0.2Ve ( 16 solar masses) - an effect that has been noted for some other high
mass X-ray binary (HMXB) systems.

Reference: MNRAS (in press)
Status: Manuscript has been accepted