The Orbital Period of the SMC X-ray Pulsar XTE J0055-727
ATel #347; R. H.D. Corbet (NASA/GSFC and USRA), C. B. Markwardt (NASA/GSFC and University of Maryland), F. E. Marshall (NASA/GSFC), M. J. Coe, W. R.T. Edge, J. L. Galache (Southampton University), S. Laycock (CfA)
on 15 Oct 2004; 20:58 UT
Credential Certification: Robin Corbet (corbet@gsfc.nasa.gov)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Regular monitoring of the Small Magellanic Cloud with the RXTE
Proportional Counter Array has revealed a periodicity in the pulsed
flux from the 18.4s X-ray pulsar XTE J0055-727, initially found to be active
in November/December 2003 (Corbet et al. 2003, ATEL #214). The source
was then not detected in weekly monitoring of the SMC until seen to
be active on May 21. The source was then next detected on: June 23, July
29, September 1, and October 7. This series of five detections can be
described by an ephemeris of:
T = MJD 53145 +/- 3 + n x 34.8 +/- 1.1
where T is the epoch of outburst and
n is the outburst cycle number.
For the purposes of determining this outburst recurrence period
we ascribed an error of +/- 3.5 days to each detection because of our
weekly sampling intervals.
This regular pattern of outbursts strongly suggests that they show the
orbital period of this system. This combination of pulse and orbital
periods is consistent with XTE J0055-727 being a Be star system (Corbet 1986,
MNRAS, 220, 1047).
The first source detections in 2003 bracket the time of a predicted
outburst and, if included in our analysis, the ephemeris of predicted
outburst becomes:
T = MJD 53145.7 +/- 1.3 + n x 34.6 +/- 0.4
A plot showing the difference between predicted and observed times of source detection is available at:
http://lheawww.gsfc.nasa.gov/users/corbet/pulsars/18.37omc.ps
We encourage observations with imaging X-ray instruments and in other
wavebands at the times of future predicted outburst which may lead to an
identification of the optical counterpart.
