Date: Mon, 11 Oct 1999 14:28:29 -0400 (EDT) From: Ron Remillard <rr@space.mit.edu> submitted IAUC, FYI (sorry if you received this earlier) Optical searches needed! Galactic coordinates approx +54.0 +8.6 XTE J1859+226 A. Wood and D. A. Smith, Massachusetts Institute of Technology (MIT); F. E. Marshall and J. Swank(Goddard Space Flight Center), report, on behalf of the RXTE All-Sky Monitor (ASM) team at MIT and Goddard Space Flight Center, the emergence of a new X-ray transient. The source's intensity was measured to rise slowly during a ~12 h interval to 160 +/- 15 mCrab (2-12 keV) 1999 Oct 9.658 (UT) and 250 mCrab by Oct 10.523, confirmed by a PCA observation. The rise was consistent with a linear increase at a rate of ~6 mCrab/h. Extrapolation indicates that the outburst began around 1999 Oct 8.55 (UT). The ASM spectrum is roughly Crab-like and shows no indication of evolution. The best localization of this source is a parallelogram with corners at (epoch J2000.0) R.A. = 18h58m.6, Decl. = +22o40'; 18h57m.7, +22o39'; 18h59m.1, 22o32'; 19h00m.0, 22o33' (90% confidence, including an estimate of systematic errors). Neither the ASM catalog nor SIMBAD records any known X-ray sources in or near this error box. A series of PCA observations are planned. Observations at other wavelengths would be timely. cheers, Ron Remillard for RXTE ASM team at MIT & GSFC