Lost and found: A new position and infrared counterpart for the X-ray binary scutum X-1

Using archival X-ray data, we find that the catalog location of the X-ray binary Scutum X-1 (Sct X-1) is incorrect and that the correct location is that of the X-ray source AX J183528- 0737, which is 15' to the west. Our identification is made on the basis of the 112 s pulse period for this object detected in an XMM-Newton observation, as well as spatial coincidence between AX J183528-0737 and previous X-ray observations. Based on the XMM-Newton data and archival RXTE data, we confirm secular spin-down over 17 yr with period derivative P approximate to 3.9 x 10(-9) s s(-1), but do not detect a previously reported X-ray iron fluorescence line. We identify a bright (K-s = 6.55) red (J - K-s = 5.51) optical and infrared counterpart to AX J183528-0737 from 2MASS, a number of mid-IR surveys, and deep optical observations, which we use to constrain the extinction to and distance of Sct X-1. From these data, as well as limited near-IR spectroscopy, we conclude that Sct X-1 is most likely a binary system composed of a late-type giant or supergiant and a neutron star.