The infrared counterpart of GX 13+1

We have discovered a bright (K = 12) infrared source which is likely the counterpart to the bright galactic bulge x-ray source GX 13+1. Observations with the MMT infrared photometer and the Rochester infrared Array camera at the IRTF allow determination of the source position to ∼0.7 arcsec, allow the infrared colors to be measured, and shows no variability on a 1 yr timescale. We consider four possible sources for the infrared emission, and conclude that it is most likely due to a K giant secondary. Future observations should allow more definite discrimination between the various possibilities. The discovery of a late-type giant secondary in GX 13+1 is contrary to the expectation that low-mass x-ray binaries (LMXB) which show quasiperiodic oscillations (QPO) have giant companions, while those which do not show QPO (like GX 13+1) have dwarf secondaries. The relation between the size of the scattered x-ray halo and the A_v inferred from the infrared observations is compared to that found in other x-ray sources.