Discovery of a new 89 second X-ray pulsar: XTE J1906+09

We report on the discovery of a new pulsating X-ray source during Rossi X-r ay Timing Explorer (RXTE) observations of a low galactic latitude field cen tered at R.A. (J2000) = 19(h)05(m)43(s), decl. (J2000) = +08 degrees 58'48 ". Significant pulsations were detected by both the Proportional Counter Ar ray and the High Energy X-ray Timing Experiment instruments aboard RXTE at a fundamental period of 89.17 +/- 0.02 s, with higher harmonics also visibl e in the 2-10 keV power spectrum. The folded light curve from the source is multiply peaked at lower energies and changes to a single-peaked morpholog y above similar to 20 keV. The phase-averaged spectrum from the source is w ell fit by strongly absorbed power-law or thermal bremsstrahlung spectral m odels of photon index 1.9 +/- 0.1 or temperature 19.5 +/- 4.6 keV, respecti vely. The mean neutral hydrogen column density is N-H approximate to 10(23) cm(-2), suggesting a distance of greater than 10 kpc to the source and a m inimum 2-10 keV X-ray luminosity of 2 x 10(35) ergs s(-1). By comparison wi th other pulsars with similar periods and luminosities, we suggest that XTE J1906+09 has a supergiant companion with an underfilled Roche lobe. We spe culate further that one of the M stars in a peculiar M star binary system m ay be the companion.