X-ray and optical follow-up observations of the August 1998 X-ray transient in NGC 6440

The BeppoSAX Wide Field Cameras detected a transient in NGC 6440 on 1998 Au g 22. ROSAT did not detect this source on 1998 Sep 8, indicating that the X -ray flux had decreased by a factor 400 at least, and/or that the X-ray spe ctrum had become appreciably softer. Analysis of archival ROSAT HRI data re veals two sources associated with NGC 6440; one of these may be the transie nt in quiescence. We have also obtained B and R images of NGC 6440 on 1998 Aug 26 and again on 1999 July 15, when the transient had returned to quiesc ence. Subtraction of these images reveals one object in the core which was brighter in B, but not in R, during the X-ray outburst. We estimate B simil ar or equal to 22.7 and (B - R)(0) less than or similar to 0 on 1998 Aug 26 , which makes it a viable candidate counterpart.