2003IAUC.8168....2M

C. B. Markwardt, University of Maryland and Goddard Space Flight Center (GSFC); A. I. Ibrahim, GSFC and George Washington University; and J. H. Swank, GSFC, report that, following reports from the IPN and HETE of renewed bursting activity by the soft gamma-ray repeater SGR 1806-20 (GCN 2297, 2308), an RXTE PCA pointed observation was undertaken that revealed unexpected x-ray pulsations at a period of 5.54 s in the PCA field-of-view (GCN 2306). An RXTE PCA scanning observation on July 18.23-18.27 UT showed a new source at R.A. = 18h10m.9, Decl. = -19o42' (equinox 2000.0), with estimated 99-percent-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, designated XTE J1810-197. The fitted flux was 2.5 ± 0.2 mCrab (2-10 keV). On hindsight, XTE J1810-197 has been detectable in RXTE PCA galactic-bulge scans since Feb. 7 (but not before), and it is steadily declining from a maximum of 3.6 mCrab. Follow-up observations are encouraged.