SIMBAD references

E. V. Gotthelf and J. P. Halpern, Columbia University; C. Markwardt, Goddard Space Flight Center (GSFC); A. I. Ibrahim, George Washington University and GSFC; M. Roberts and S. M. Ransom, McGill University; and P. Woods, USRA and National Space Science and Technology Center, on behalf of a larger collaboration, report a highly significant detection of a pulsed source with a barycentric period of 5.5391(3) s, from a 2833-s Chandra HRC-I observation starting Aug. 27.95166 UT. This source shows a strongly modulated (52-percent pulsed fraction) sinusoidal pulse signal with a countrate of 0.917 counts/s in the HRC-I energy band 0.08-10.0 keV. The pulsar is located at R.A. = 18h09m51s.13, Decl. = -19o43'51".7 (equinox 2000.0; uncertainty radius of 2".1 at the off-axis HRC-I position). This position is offset by 14' from the centroid reported for the 5.5-s pulsar RXTE J1810-197 (IAUC 8168); the large offset (6 sigma) is likely due to systematic errors in the derived RXTE position which are based on scans of the complex region. The location of CXOU J180951.1-194351 is consistent with a source seen in archival ROSAT and ASCA images. The lack of an optical counterpart within the 1-sigma Chandra error circle suggests that CXOU J180951.1-194351 is an isolated neutron star, one most similar to the transient anomalous x-ray pulsar AX J1844.8-0256 (cf. Vasisht et al. 2000, Ap.J. 43, L49)."