GRO J0422+32: The lowest mass black hole?

We have obtained optical and infrared photometry of the soft X-ray transient GRO J0422+32. From this photometry, we find a secondary star spectral type of M1, and an extinction of A(V) = 0.74 +/- 0.09. We present the first observed infrared (J-, H-, and K-band) ellipsoidal variations, and model them with WD98, a recent version of the Wilson-Devinney light curve-modeling code. Assuming no significant contamination of the infrared light curves, we find a lower limit to the inclination angle of 43degrees corresponding to an upper limit on the mass of the compact object of 4.92 M.. Combining the models with the observed spectral energy distribution of the system, the most likely value for the orbital inclination angle is 45degrees +/- 2degrees. This inclination angle corresponds to a primary black hole mass of 3.97 +/- 0.95 M.. Thus, we contend that J0422+32 contains the lowest mass stellar black hole reported, and the first to have a measured mass that falls in the 3-5 M. range.