2023ApJ...954L..25B

We report the detection of the millimeter CH₃OH masers including a new detection of class I (11_0,11-10_1,10A) and class II (6_1,5-5_2,4E) maser transitions toward the high-mass protostar S255IR NIRS3 in postburst phase. The CH₃OH emissions were detected as a mixture of maser and thermal characteristics. We examine the detected transitions using an excitation diagram and local thermodynamic equilibrium model spectra and compare the observed properties with those of thermal lines. Class II CH₃OH maser transitions showed distinctive intensity and velocity distributions from those of thermal transitions. Bright, distinct emission components in addition to the fragmented and arc-shaped emissions are only detected in class I CH₃OH maser transitions toward southern and western directions from the protostellar position, implying the presence of the slow outflow shocks.