star (its position outside the core suggests this is less likely).

It is difficult to estimate NGC 6440 X-2’s mass transfer rate, due to its extreme faintness and the limitations of existing surveys. We identify two limiting cases, one based on its recent outburst history, and one using the full bulge scan light curve. For the first case, we estimate the outbursts as lasting 3 days at an average $L_X\sim1.5\times10^{36}$ , and occurring every 31 days. For canonical neutron star mass and radius estimates, this gives a time-averaged mass accretion rate of $3\times10^{-11}$ [${M_{\odot}}$]{}/year. Although this represents the mass transfer rate over the past few months, it is clear that NGC 6440 X-2 has not shown such outbursts regularly over the entire bulge scan epoch, where only 5 outbursts have been identified. Assuming (generously) that 2/3 of all outbursts have been missed (the October and November outbursts were missed by bulge scans, and it seems likely that outbursts in June/July and April/May were missed; Fig. \[fig:lcurve\]), and that the average outburst is like those seen so far, we estimate NGC 6440 X-2’s mass transfer rate over the entire bulge scan epoch (10 years) as $1.3\times10^{-12}$ [${M_{\odot}}$]{}/year. This latter rate is 