<div> Almost all 6.7 GHz methanol masers are known to be associated with high-mass protostellar objects. Until now, >1000 objects associated with this maser were detected. Non-periodic sudden flux rises with the factor of 10-1000 were detected for 4 sources (S255IR-IRS3, NGC6334I-MM1, G358.93-0.03, and G24.33+0.14). These flux rises were confirmed to be the results of the accretion burst from NIR/FIR/(Sub-)mm follow-up observations.</div><div> We have started high-cadence monitoring observations of 6.7 GHz methanol masers from Dec./2012 using Hitachi 32-m antenna[1]. Observations are conducted basically every day toward all sources (~450) with Decl. > -30 deg. The cadence varies by sources: one observation in 1-50 days. We have detected 5 sources with sudden flux rises in 2019-2022, including G358.93-0.03.</div><div> G358.93-0.03 is the first source whose sudden flux rise was discovered after the establishment of the Maser Monitoring Organization (M2O[2]). Only three days after the discovery at Hitachi 32-m, we have circulated to M2O. We have also submitted to Astronomer's Telegram[3]. These quick circulations have led to the first detections of many new maser emission lines[4, 5, 6, 7], detection of the propagation of the "heat-wave"[8], detection of the spiral structure[9, 10], and the confirmation of the accretion burst by FIR observations[11].</div><div> The data obtained at Hitachi 32-m are available at "Ibaraki 6.7 GHz class II methanol maser database (iMet)"[12].</div><div>[1] Yonekura et al. 2016, PASJ, 68, 74.</div><div>[2] https://www.masermonitoring.com/</div><div>[3] Sugiyama et al. 2019, ATel, 12446.</div><div>[4] Breen et al. 2019, ApJ, 876, 25</div><div>[5] MacLeod et al. 2019, MNRAS, 489, 3981-3989</div><div>[6] Brogan et al. 2019, ApJL, 881, L39</div><div>[7] Chen et al. 2020, ApJL, 890, L22</div><div>[8] Burns et al. 2020, Nat.Astron., 4, 506-510</div><div>[9] Chen et al. 2020, Nat.Astron., 4, 1170-1176</div><div>[10] Burns et al. 2023, Nat.Astron, in press</div><div>[11] Stecklum et al. 2021, A&A, 646, A161</div><div>[12] http://vlbi.sci.ibaraki.ac.jp/iMet/</div>
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