We present multiband optical/infrared photometry of V4580 Sgr , the optical counterpart of the accretion-powered millisecond pulsar SAX J1808.4–3658 , taken during the 1998 X-ray outburst of the system .
The optical flux is consistent with emission from an X-ray–heated accretion disk .
Self-consistent modeling of the X-ray and optical emission during the outburst yields best-fit extinction A _ { V } = 0.68 ^ { +0.37 } _ { -0.15 } and inclination \cos i = 0.65 ^ { +0.23 } _ { -0.33 } ( 90 % confidence ) , assuming a distance of 2.5 kpc .
This inclination range requires that the pulsar ’ s stellar companion has extremely low mass , M _ { c } = 0.05–0.10 M _ { \odot } .
Some of the infrared observations are not consistent with disk emission and are too bright to be from either the disk or the companion , even in the presence of X-ray heating .