The high-mass young stellar object G358.93-0.03 underwent an accretion burst during the period from 2019 January to June. Given its extraordinary conditions, a number of new maser transitions may have been naturally excited during the burst stage. Searching for new maser lines and monitoring maser variability associated with the accretion burst event are important for understanding the complex conditions of the massive star formation toward G358.93-0.03. In this work, using the Shanghai 65 m Tianma Radio Telescope, we continuously monitored the multiple maser (including methanol and water) transitions toward G358.93-0.03 during the burst in the period from 2019 March 14 to May 20. There were 23 CH3OH maser transitions and one H2O maser transition detected from the monitoring. Nearly all the detected maser transitions toward this source have dramatic variations in their intensities within a short period of ∼2 months. Eight new methanol transitions from G358.93-0.03 were identified to be masering in our observations based on their spectral profile, line width, intensity, and the rotation diagram. During the monitoring, the gas temperature of the clouds in the case of saturated masers can show a significant decline, indicating that the maser clouds were going through a cooling process, possibly associated with the propagation of a heat wave induced by the accretion burst. Some of the maser transitions were even detected with the second flares in 2019 April, which may be associated with the process of the heat-wave propagation induced by the same accretion burst acting on different maser positions.

We present a statistical study of infrared variability using the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) database for a sample consisting of 1085 high-mass young stellar objects (YSOs) related to 6.7 GHz methanol masers. A total of 383 maser sources were identified as NEOWISE variables and classified in two variability behavior classifications: 204 secular (linear, curved, and periodic) and 179 stochastic (burst, drop, and irregular) variables. Statistical analysis of the properties of these variables (e.g., the dust temperature, bolometric luminosity, hydrogen column density, W4 luminosity, and W1−W2 color) has revealed a potential evolutionary sequence among different light-curve types of variables. There is a possible general evolutionary (from less to more evolved) trend between the three variable types from secular to stochastic to nonvariable. For the specific classifications, the evolutionary trend for secular variables is linear to sin to sin+linear, and for stochastic variables it is burst to irregular to drop. These sequences may reflect the evolution of the envelope or accretion disk of high-mass YSOs, from large to small radii due to gravitational collapse. Although no significant variability correlation was established between the 6.7 GHz methanol maser and the W2-band emission based on the data collected so far, a number of candidates were found for further investigating the accretion burst events via future variability monitoring programs of both mid-infrared emission and masers.

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