NTT $R$ frame; upper right, new Gemini $g'$ frame; lower left,  WFPC2 $V$ frame; lower right,  WFPC2 $B$ frame. All 19” $\times$ 14”, with N at top. ](f6.eps)

![ \[fig:ISPI\] Infrared ISPI images (each 25”$\times$25”, N at top) with the CTIO 4-m on the dates specified. Top, images in $J$; bottom, images in $K$. Circles (0.8” in radius) indicate the positions of NGC 6440 X-2. ](f7.eps)

We obtained three 500 s frames in each of $g'$ (note that the $g'$ bandpass is between $V$ and $B$) and $r'$ using Gemini-South GMOS-S on Sept. 1, 2009, during the outburst decay (program GS-2009B-DD-2). Unfortunately the $r'$ frames were saturated at the location of the transient, but the $g'$ frames provided our best optical outburst limit (Fig. \[fig:optical\]). No star was seen within 0.8($4\sigma$) of the transient position. An approximate calibration of the $g'$ images was obtained using a star by star comparison with the $B,~V$ photometry of @Martins80. We determined the detection limit for stars within an annulus about the cluster center containing the location of the transient. Based on the faintest 5% of the stars in the annulus, the estimated detection limit is $g' \sim 22.0$. Thus we adopt $g'>22$ as 