Variable Outer Disk Shadowing around the Dipper Star RXJ1604.3-2130

Low brightness dips have recently been observed in images of protoplanetary disks, and they are believed to be shadows by the inner disk. We present VLT/SPHERE polarimetric differential imaging of the transition disk around the dipper star RX J1604.3-2130. We gathered 11 epochs that cover a large temporal baseline, to search for variability over timescales of years, months, weeks, and days. Our observations unambiguously reveal two dips along an almost face-on narrow ring (with a width of similar to 20 au), and the location of the peak of this ring is at similar to 65 au. The ring lies inside the ring-like structure observed with ALMA, which peaks at similar to 83 au. This segregation can result from particle trapping in pressure bumps, potentially due to planet(s). We find that the dips are variable, both in morphology and in position. The eastern dip, at a position angle (PA) of similar to 83 degrees.7 +/-. 13 degrees.7, has an amplitude that varies between 40% to 90%, and its angular width varies from 10 degrees to 34 degrees. The western dip, at a PA of similar to 265 degrees.90, +/-. 13 degrees.0, is more variable, with amplitude and width variations of 31% to 95% and 12 degrees to 53 degrees, respectively. The separation between the dips is 178 degrees. 3 +/-. 14 degrees. 5, corresponding to a large misalignment between the inner and outer disks, supporting the classification of J1604 as an aperiodic dipper. The variability indicates that the innermost regions are highly dynamic, possibly due to a massive companion or to a complex magnetic field topology.