Discovery of Six New Class II Methanol Maser Transitions, Including the Unambiguous Detection of Three Torsionally Excited Lines toward G 358.931-0.030

Abstract

We present the unambiguous discovery of six new class II methanol maser transitions, three of which are torsionally excited (vt= 1). The newly discovered 6.18 GHz 17-2→ 18-3E (vt= 1), 7.68 GHz 124→ 133A- (vt= 0), 7.83 GHz 124→ 133A+ (vt= 0), 20.9 GHz 101→ 112A+ (vt= 1), 44.9 GHz 20→ 31E (vt= 1), and 45.8 GHz 93→ 102E (vt= 0) methanol masers were detected toward G 358.931-0.030, where the known 6.68 GHz maser has recently been reported to be undergoing a period flaring. The detection of the vt= 1 torsionally excited lines corroborates one of the missing puzzle pieces in class II maser pumping, but the intensity of the detected emission provides an additional challenge, especially in the case of the very highly excited 6.18 GHz line. Together with the newly detected vt= 0 lines, these observations provide significant new information that can be utilized to improve class II methanol maser modeling. We additionally present detections of 6.68, 19.9, 23.1, and 37.7 GHz class II masers, as well as 36.2 and 44.1 GHz class I methanol masers, and provide upper limits for the 38.3 and 38.5 GHz class II lines. Near simultaneous Australia Telescope Compact Array observations confirm that all 10 of the class II methanol maser detections are co-spatial to ∼0.2 arcsec, which is within the uncertainty of the observations. We find significant levels of linearly polarized emission in the 6.18, 6.67, 7.68, 7.83, 20.9, 37.7, 44.9, and 45.8 GHz transitions, and low levels of circular polarization in the 6.68, 37.7, and 45.8 GHz transitions. © 2019. The American Astronomical Society. All rights reserved.