A huge eclipse in the young star RW Aur

This is the lightcurve of the young star RW Aur taken from the archive of the AAVSO (i.e. amateur observations). Plot created in summer 2011, to illustrate the huge eclipse-type event between December 2010 and March 2011, which I found by accident. The eclipse depth is 1.9 mag, meaning that only about 1/6 of the flux of the star is visible during the eclipse. In total, the eclipse lasts 260 days, with ingress and egress of about 100 days each.

Since the ingress and egress take so long, the occulting body cannot have sharp edges. One possible explanation is that we witnessed an eclipse by a dense cloud of dust and gas in the disk that surrounds RW Aur. This cloud could either be temporary, or it could move across the star due to the Keplerian rotation of the disk. In the second scenario, the cloud would be at least ~20AU away from the star (i.e. the distance Sun-Uranus).

Based on the AAVSO archive, such eclipses are extremely rare in RW Aur; no similar event is seen back to 1950. As far as I can tell, no further follow-up observations were carried out during this eclipse, which makes it very difficult to speculate on the exact origin.