  MERLIN and VLBA observations of the 1720 MHz maser emission from the OH
molecule in the supernova remnant IC443 are presented. Based on MERLIN data
with a resolution of 160 mas, the deconvolved sizes of the maser sources are in
the range 90 to 180 mas (135 to 270 AU). The 12 mas resolution VLBA images show
compact cores with sizes in the range 15 to 55 mas. The maser brightness
temperatures are (2-34)x10^6 K for the MERLIN sources and (5-19)x10^8 K for the
VLBA cores, in agreement with theory. Unlike the Zeeman Stokes V profiles
observed in other OH (1720 MHz) SNR masers, single-handed circular polarization
line profiles are observed in IC443 on all angular scales from 1000 to 10 mas
resolution. For one line component, the observed line width is 0.24+/-0.07
km/s, compared to an estimated Doppler width of 0.49 km/s. This discrepancy in
line widths can be accounted for if the maser emission arises from an elongated
ellipsoidal region of masing gas.
