VLA observations of 5-GHz excited OH lines towards SGR B2.

The quasi-thermal emission associated with the 4660- and 4750-MHz transitions of the J = 1/2 excited state of OH has been mapped across Sgr B2 with an angular resolution of 3 arcsec. This emission is concentrated towards portions of the three main continuum complexes, which are disposed along a N-S line. For two of these complexes the emission is more or less consistent with LTE, being considerably stronger at 4750 than at 4660 MHz. However, towards the main complex near 17^h44^m10^s, -28°22arcmin the line emission is anomalous. Not only do the relative peak intensities reverse, but there are velocity shifts between the line profiles for the two transitions. Weak narrow-band 4600-MHz maser emission is located near a 1612-MHz ground-state OH maser, close to a compact continuum component in the main complex. In contrast, the third excited-state transition, at 4765 MHz, is seen as a brighter narrow-band maser located close to a 1720-MHz ground-state maser, towards another compact component 8 arcsec further south.