2005A&A...433L..29S

We report the discovery of a burst of highly polarized OH maser emission at 1612MHz in the proto-planetary nebula candidate OH17.7-2.0. The total flux density of two red-shifted features at 72.8 and 73.3km/s increased nearly threefold over a period of ∼430days. This burst was not associated with any systematic changes of the other 1612MHz maser features as well as of the 1665 and 1667MHz masers. The burst was characterized by a linear growth of left-hand circularly polarized emission accompanied by considerable linearly polarized emission. During the burst, the degrees of circular and linear polarization increased up to -80% and 15% respectively. A relation found between the line width and the peak flux density of the two bursting features implies a saturated amplification. Among several possible causes of the burst, a local propagation effect due to Zeeman overlap initiated by evolutionary changes in the shell appears most plausible.