High-resolution studies of the C-band and L-band radio continuum of the periodic methanol maser source G9.62+0.20E and surrounding sources

High-resolution observations oftheC-band and L-band radio continuum ofthe hypercompact H II region G9.62+0.20E conducted with the e-MERLIN interferometric array are presented. A flux density of 2.25 ± 0.20 mJy and an angular size of 127 ± 22 mas were measured for the C-band continuum. At L band, an upper limit of 162 μJy on the integrated flux density was calculated at the continuum’s position. The surrounding sources C and D were detected at levels consistent with previous detections. The results for source E requires a steeper spectrum at L band than previous observations extrapolated from higher frequencies. This can be explained with a truncated inverse square law density distribution model. We obtain a C-band peak brightness temperature of about 4000 K, which assuming an electron temperature of 104K translates to an optical depth of 0.5, indicating the continuum is optically thin at C band going thick at L band. These results therefore place firm constraints on H II region models in source E. The periodic variability of methanol masers, as seen in G9.62+0.20E, has been explained with the pulsating star, accretion disc, and colliding wind binary models. Some models predict a hypercompact H II region can provide pumping for methanol masers. In the colliding wind binary model context maser variability is attributed to seed photon modulation. Hence, future H II models matching our observations could test predictions of these models in terms of the variability profiles of the 1.6 GHzOH and 6.7 GHz methanol masers.