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Orbit Solution for the Millisecond Pulsar IGR J00291+5934

ATel #360; C. B. Markwardt (U. Maryland & GSFC), D. K. Galloway (MIT), D. Chakrabarty (MIT), E. H. Morgan (MIT), T. E. Strohmayer (GSFC)
on 7 Dec 2004; 03:07 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 1660

The INTEGRAL Transient IGR J00291+5934 (ATEL #352), now known to be a 1.67 millisecond X-ray pulsar (ATEL #353), was observed by the RXTE PCA on Dec 5 and 6. The source has decayed to approximately 27 mCrab (2-10 keV).

The data were barycentered using the Fox & Kulkarni optical counterpart position (ATEL #354). Pulsations with a sinusoidal frequency modulation are clearly detected in each observation. The best fitting orbit has a period of 147.412 +/- 0.006 min and an a_x sin(i) of 65.0 +/- 0.2 lt-ms. The mass function is 2.81e-5 +/- 0.02e-5 M_sun. Assuming a neutron star of mass 1.4 M_sun, the companion mass must be larger than 0.038 M_sun.

The orbit and inferred companion of IGR J00291+5934 appear to be very similar to that of SAX J1808.4-3658, the first known millisecond X-ray pulsar.

There is presently no evidence of X-ray eclipses or X-ray bursts.

RXTE continues to observe the source.