Be/X-ray binaries exhibit two types out X-ray outburst. Type I outbursts occur with each binary orbital period while Type II outbursts last a few orbital periods and show no orbital modulation. Below is a figure from Kretschmar (2013) that shows the two different types of Be/X-ray binary outbursts.

Recently we found a potential explanation for the two types of outburst (Martin et al. 2014). Since the orbit of the binary is eccentric, the Type I outbursts occur at periastron. The Be disc is likely to be misaligned to the binary orbital plane. If the inclination is above the critical KL angle, of about 40 degrees, then the disc is unstable to KL oscillations. The eccentricity of the disc increases while the inclination decreases. The eccentric disc then interacts more strongly with the companion leading to a large amount of mass transfer to the neutron star and a Type II X-ray outburst. The figure below shows the result of our simulation. Note that we do not model the disc around the neutron star. We predict that this would have the effect of smoothing out this accretion curve.