XTE J1810-197 is Likely an Anomalous X-ray Pulsar
ATel #188; C. B. Markwardt (U. Maryland & GSFC), S. Ransom (McGill), P. Woods (NSSTC), A. Ibrahim (GWU & GSFC), V. Kaspi (McGill), C. Kouveliotou (NSSTC), M. Roberts (McGill) & J. Swank (GSFC)
on 11 Sep 2003; 02:02 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, A Comment, Neutron Star, Soft Gamma-ray Repeater, Transient, Pulsar
Referred to by ATel #: 193
The recently discovered pulsar, XTE J1810-197, now also known as CXOU
J180951.1-194351, AX J1809.8-1943 and 1RXS J180951.5-194345 (IAUC
8168 , IAUC 8190 ), has been observed by the RXTE PCA from 2002 to
present. These observations include pointings of other targets which
included XTE J1810-197 in the field of view, galactic bulge monitoring
scans, and dedicated pointings. Based on galactic bulge scans, the
source reached a maximum 2-10 keV flux of 3.5 mCrab in Feb 2003,
declined to about 2 mCrab, and has stabilized at that level.
Pulsations at 5.54 s were first detected Jan 23, 2003, and continue to
the most recent observations. We have been able to construct a phase
coherent solution of all the pulse times of arrival. Both polynomial
and spline models are sufficient to describe the frequency evolution,
with rms timing residuals of ~0.15 seconds. At the epoch of Jul 28,
2003, we find a pulse period of 5.5392993(3) s, and a mean pulse
period derivative of 1.8 x 10^{-11} s/s, with significant excursions
due to apparent torque noise. We formally cannot rule out a long
period binary modulation (> 200 days), however such a long period and
large Doppler frequency shifts would be inconsistent with most known
X-ray binaries.
Assuming no orbit, the period derivative is consistent with those of
other anomalous X-ray pulsars. Combined with the previously reported
spectral shape and pulse period (ATEL #167), we conclude that this
source is also an anomalous X-ray pulsar.
