disk and lower mass transfer rate (e.g. Deloye & Bildsten 2003). However, we are not aware of detailed modeling of outbursts of hydrogen-poor accretion disks with extreme mass ratios (and thus likely superhumps, Whitehurst 1988), suggesting an avenue for further study.

The X-ray record suggests that NGC 6440 X-2’s activity has significantly increased in the past year. It would be difficult to attribute this change to the disk (as it includes numerous outburst cycles), and we suggest that it represents a signal of mass-transfer variations from the donor. Cyclical variations in the orbital period are well-established in longer-period cataclysmic variables [@Borges08], LMXBs [@Wolff09], and black widow pulsars [@Arzoumanian94] and seem likely to be due to magnetic activity in the companion star. Such activity has also been suggested to explain SAX J1808.4-3658’s large current rate of orbital period increase [@Hartman08], and decades-long variations in mass transfer rates in LMXBs [@Durant09]. If such a mechanism is active here, it requires a partly nondegenerate, convective companion. Alternatively, the increased activity could indicate a change in the orbital parameters, induced by a distant companion (making this a triple system; testable with monitoring of future outbursts by RXTE) or a recent close interaction with another 