A Remarkable Low‐Mass X‐Ray Binary within 0.1 Parsecs of the Galactic Center

Recent X-ray and radio observations have identified a transient low-massX-ray binary (LMXB) located only 0.1 pc in projection from the Galactic center,CXOGC J174540.0-290031. In this paper, we report the detailed analysis of X-rayand infrared observations of the transient and its surroundings. Chandrabservations detect the source at a flux of F_X = 2e-12 erg cm^-2 s^-1 (2-8keV). After accounting for absorption both in the interstellar medium and inmaterial local to the source, the implied luminosity of the source is only L_X= 4e34 erg/s (2-8 keV; D=8 kpc). However, the diffuse X-ray emission near thesource also brightened by a factor of 2. The enhanced diffuse X-ray emissionlies on top of a known ridge of dust and ionized gas that is visible infraredimages. We interpret the X-ray emission as scattered flux from the outburst,and determine that the peak luminosity of CXOGC J174540.0-290031 was >2e36erg/s. We suggest that the relatively small observed flux results from the factthat the system is observed nearly edge-on, so that the accretion diskintercepts most of the flux emitted along our line of sight. We compare theinferred peak X-ray luminosity to that of the radio jet. The ratio of the X-rayto radio luminosities, L_X/L_R<1e4, is considerably smaller than in other knownLMXBs (> 1e5). This is probably because the jets are radiating with unusuallyhigh efficiency at the point where they impact the surrounding interstellarmedium. This hypothesis is supported by a comparison with mid-infrared imagesof the surrounding dust. Finally, we find that the minimum power required toproduce the jet, L_jet~1e37 erg/s, is comparable to the inferred peak X-rayluminosity. This is the most direct evidence yet obtained that LMXBs accretingat low rates release about half of their energy as jets.Comment: 11 pages, including 9 figures (6 color). submitted to Ap