A New Eclipsing X-Ray Burster near the Galactic Center: A Quiescent State of the Old Transient A1742—289

With ASCA, we found highly absorbed X-rays from the position of the bright transient source A1742–289 with a variable flux ranging from 8 × 10−12 to 4 × 10−11 erg s−1 cm−2 in the 3–10 keV band. We discovered an X-ray burst and eclipses from A1742–289, establishing that A1742–289 is an eclipsing low-mass X-ray binary. Using the black-body radius during an X-ray burst, we estimated the distance of A1742–289 to be about 10 kpc, or near to the galactic center. The burst peak flux was then found below the Eddington limit of a neutron star. Excess soft X-rays during the eclipse were detected, which are interpreted to be scattering by interstellar dust-grains. Since A1742–289 was found to be an X-ray emitter, even in the quiescent state with a moderate but variable flux, and since A1742–289 is lying only 1′.3 from the galactic center, previously reported X-ray fluxes of the galactic center (Sgr A*) with non-imaging instruments might have suffered due to possible contamination of A1742–289.