Two Rapidly Variable Galactic X-ray Transients Observed with Chandra, XMM and Suzaku

TL;DR

This paper reports the discovery and analysis of two rapidly variable X-ray transients near the Galactic center, revealing their spectral properties, variability, and potential classifications as symbiotic or low-mass X-ray binaries.

Contribution

The study identifies two new Galactic X-ray transients with detailed spectral and variability analysis, suggesting their possible classifications and contributing to understanding of such transient sources.

Findings

Both sources show strong, rapid variability on timescales of tens to thousands of seconds.

XMMU J174445.5-295044 likely a symbiotic star or X-ray binary.

CXOU J174042.0-280724 is an unusual low-mass X-ray binary candidate.

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 N_H variability, and hard spectra. XMMU J174445.5-295044 is seen at 2-10 keV fluxes of 3*10^{-11} to <10^{-12} ergs/cm^2/s, with N_H at or above 5*10^22 cm^{-2}, by XMM, Chandra, and Suzaku. A likely 2MASS counterpart with K_S=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} ergs/cm^{-2}/s, with large N_H variations (from 2*10^22 to >2*10^23 cm^{-2}). No 2MASS counterpart is visible, to K_S>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.