2003CBET...36....1M

C. B. Markwardt, University of Maryland and Goddard Space Flight Center (GSFC), A. I. Ibrahim (GSFC, The George Washington University), and J. H. Swank (GSFC), report: "Based on reports from the IPN and HETE of renewed bursting activity by the soft gamma repeater SGR 1806-20 (GCN 2297, 2308), an RXTE PCA pointed observation was undertaken, which revealed unexpected X-ray pulsations at a period of 5.54 s in the PCA field of view (GCN 2306). We obtained an RXTE PCA scanning observation Jul 18.23-18.27 (UT). A new source was detected, whose position is, R.A. = 18h10.9m, Decl. = -19o42' (equinox 2000.0), with estimated 99% confidence semi-major axes of 5' in R.A. and 7' in Decl. This confidence region excludes both the reported IPN burst annuli and the HETE burst error region, and is not consistent with any other known pulsar. The pulsations are clearly from this source, which we designate XTE J1811-197. The fitted flux was 2.5 ± 0.2 mCrab (2-10 keV). On hindsight, XTE J1811-197 has been detectable in RXTE PCA galactic bulge scans since Feb 7, 2003 (but not before), and it is steadily declining from a maximum of 3.6 mCrab. Follow-up observations are encouraged."