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Burst Oscillations from IGR J17191-2821 Imply a 294 Hz Spin Frequency

ATel #1068; C. B. Markwardt (CRESST/U. Maryland/NASA/GSFC); M. Klein-Wolt (U. Amsterdam); J. H. Swank (NASA/GSFC); R. Wijnands (U. Amsterdam)
on 6 May 2007; 18:27 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)

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

Referred to by ATel #: 1069, 1070, 1075, 1096, 4170

The X-ray transient IGR J17191-2821 was detected by INTEGRAL (ATEL #1021) and shown to have a rapid variability and decay (ATEL #1022, ATEL #1025). A more recent report of activity by RXTE and Swift (ATEL #1065) has revealed X-ray bursts, identifying this source as a neutron star system. Recent PCA data suggests a decline from outburst peak.

In an RXTE PCA observation on 2007 May 4 (01:33 UTC), we detect a 2-10 keV persistent flux level of about 85 mCrab. An X-ray burst was also detected, and a dynamical power spectrum shows high frequency oscillations during the burst. The oscillation frequency drifted from about 292 Hz to 294 Hz, which is consistent with the behavior of burst oscillation detections from other sources. It is likely that the neutron star spin frequency is near the maximum oscillation frequency, or 294 Hz. This spin frequency is fairly typical in comparison to other burst oscillation detections.

We searched for coherent pulsations in the persistent X-ray emission near the burst oscillation frequency, but found none. There are also no strong high frequency QPOs.

The peak burst X-ray flux was about 2.3E-11 erg/s/cm^2 (bolometric, unabsorbed). By the same arguments of Klein-Wolt et al (ATEL #1065), the new distance upper limit would be ~11 kpc. This would place the source reasonably close to the galactic center.