EVN observations of an OH maser burst in OH17.7-2.0

TL;DR

This study reports EVN observations of a rare, intense OH maser burst in the proto-planetary nebula candidate OH17.7-2.0, revealing interaction between a jet-like outflow and the remnant shell, with highly polarized emission indicating energetic processes.

Contribution

First high-resolution localization of an OH maser burst in a proto-planetary nebula, linking maser activity to jet-shell interactions and polarization signatures.

Findings

Maser emission originates from an incomplete spherical shell.

Evidence of jet-shell interaction causing the burst.

Highly polarized emission with brightness temperatures up to 10^11K.

Abstract

We have observed the OH 1612-MHz maser emission towards the proto-planetary nebula candidate OH17.7-2.0 that underwent a very strong and unusual outburst in 2003. Phase-referencing data were obtained with the EVN in order to localize the outburst and to examine its possible causes. The majority of the emission comes from an incomplete spherical shell with inner and outer radii of 220 and 850 mas, respectively. There is a strong evidence for maser components that arise due to the interaction of a jet-like post-AGB outflow with the remnant outer AGB shell. The most prominent signature of such an interaction is the strongly bursting polarized emission near 73.3km/s coming from two unresolved components of brightness temperature up to 10^11K located at the edge of the biconal region 2500 AU from the central star. It is remarkable that this OH biconal region is well-aligned with the polar outflow inferred from the near-infrared image.