Two rapidly variable galactic x-ray transients observed with chandra, XMM-Newton, and Suzaku

Abstract

We have identified two moderately bright, rapidly variable transients in new and archival X-ray data near the Galactic center. Both objects show strong, flaring variability on timescales of tens to thousands of seconds, evidence of NH variability, and hard spectra. XMMU J174445.5-295044 is seen at 2-10 keV fluxes of 3 × 10-11 to <10-12 erg cm-2 s-1, with NH at or above 5 × 10 22 cm-2, by XMM-Newton, Chandra, and Suzaku. A likely Two Micron All Sky Survey (2MASS) counterpart with KS = 10.2 shows colors indicative of a late-type star. CXOU J174042.0-280724 is a likely counterpart to the fast hard transient IGR J17407-2808. Chandra observations find F X (2-10 keV) 10-12 erg cm-2 s-1, with large NH variations (from 2 × 1022 to >2 × 1023 cm-2). No 2MASS counterpart is visible, to KS >13. XMMU J174445.5-295044 seems likely to be a new symbiotic star or symbiotic X-ray binary, while CXOU J174042.0-280724 is more mysterious, likely an unusual low-mass X-ray binary. © 2009 The American Astronomical Society. All rights reserved.