Three-month Monitoring of the Variability toward W51 IRS2 with Ammonia, Water, and Methanol Transitions

Abstract A four-epoch monitoring program spanning ?three months (from 2020 January 8 to April 7) for ammonia, water, and methanol transitions toward the high-mass star-forming region W51 IRS2 was conducted using Shanghai 65 m Tianma Radio Telescope with its K -band (18–26.5 GHz) receiver. In total, 33 ammonia 16 were detected target at least once during this program. Among them, 14 4 show maser emission characteristics. Rapid variabilities (including both increases decreases) in from thermal emissions three of monitoring. addition, H 2 O masers obvious variability also detected. The results rotation diagram analysis quasi-thermal variations their rotational temperatures derived larger upper energies ( E u / ? ) generally decreased over whole period, 7, but those smaller first increased 1, then rapidly 1 7. These findings support suggestion that an inside-out heatwave propagation involved accretion burst a short duration (only on order months) caused drastic behaviors different line star formation.