M17 MIR: A Massive Protostar with Multiple Accretion Outbursts ^*

We report the discovery of a massive protostar M17~MIR embedded in hot molecular core M17. The multiwavelength data obtained during 1993--2019 show significant mid-IR (MIR) variations, which can be split into three stages: decreasing phase 1993.03--mid-2004, quiescent from mid-2004 to mid-2010, and rebrightening mid-2010 until now. variation 22\,GHz H$_2$O maser emission, together with MIR variation, indicates an enhanced disk accretion rate onto phases. Radiative transfer modeling spectral energy distributions 2005 epoch (quiescent) 2017 (accretion outburst) constrains basic stellar parameters M17~MIR, is intermediate-mass (M~5.4 Msun) ~1.1x10^-5 Msun ~1.7x10^-3 Msun/yr epoch. outburst induces luminosity $\Delta L\approx7600 $Lsun. In outburst, larger radius required produce consistent value estimated kinematics water masers. M17 shows two outbursts ($\Delta t\sim 9-20$ yr) magnitudes 2 mag, separated by 6 yr phase. outbusrt occupies 83\% time over 26 yr. variable amplitude much lower than contrast between extreme youth suggests that minor bursts are frequent earliest stages star formation.