Infrared Photometric Variability of GX13+1 and GX17+2

Abstract

We present infrared photometry of the Galactic Bulge X-ray binary systems GX13+1 and GX17+2 obtained in 1997 July and August using OSIRIS on the 1.8m Perkins Telescope at Lowell Observatory. GX13+1 clearly varies over ~0.6 magnitudes in the K-band. Our light curve suggests a modulation on a timescale of ~20 days, which is in agreement with previously proposed orbital periods for the system. The IR counterpart of GX17+2 is also variable in the K-band over \~0.8 magnitudes on a timescale of days to weeks, extending the variability first seen by Naylor, Charles, & Longmore (1991). We discuss the implications our data have for Deutsch et al's (1999) identification of ``star A'' as the true IR counterpart of GX17+2. The variability observed in our photometry of the blend of star A and the foreground star NP Ser implies a ~4 magnitude intrinsic variation in the K-band for GX17+2.