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
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.
