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IGR J00291+5934 is a 598 Hz X-ray Pulsar

ATel #353; C. B. Markwardt (U. Maryland and GSFC), J. H. Swank (GSFC), T. E. Strohmayer (GSFC)
on 4 Dec 2004; 20:29 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

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

Referred to by ATel #: 354, 360, 364, 1660

IGR J00291+5934 (Eckert et al. 2004, ATel #352) was observed by the RXTE PCA instrument on Dec. 3, 2004 at 06:17 (UTC) for approximately 2000 seconds exposure. The source was detected with a flux of 35 mCrab (2-10 keV).

Pulsations were detected at a barycentric frequency of 598.88 Hz, with a pulsed amplitude of approximately 6%. There is no evidence of any harmonics at half or double this frequency, suggesting that it is the fundamental rotation period of a neutron star. During the 2 ks observation the frequency drifts by approximately 36 mHz, in a manner consistent with Doppler orbital modulation. The suggested orbital period is in the 2-4 hour range, with an a_x sin(i) value of 50-100 lt-ms. IGR J00291+5934 appears to be the fastest known X-ray millisecond pulsar system.

The X-ray spectrum is consistent with an absorbed power law, with photon index 1.7 and absorption column n_H = 7e21 cm-2. The fluxes in the 2-10 and 10-40 keV X-ray bands are 6.1e-10 and 9.2e-10 erg s-1 cm-2.

Significant low frequency variability is also detected, consistent with approximate f^{-0.45} noise, with a total amplitude from 1 mHz to 1 Hz of 18%.

XTE is planning more observations to occur as soon as possible.