Flare of methanol maser in G107.298+5.639 in September happened 2 days earlier than expected

ATel #12066; A. Aberfelds (Ventspilse Obs.,Latvia), I. Smeld (Ventspilse Obs.,Latvia), A. M.Sobolev (Ural State Univ.,Russia), A. P.Bisyarina (Ural State Univ.,Russia), Alexander Tolmachev (Lebedev Physical Institute, Moscow, Russia), A. M. Tatarnikov (Moscow State Univ., Russia)
on 26 Sep 2018; 23:14 UT
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Credential Certification: Alexander Tolmachev (tolm@prao.ru)

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A rapid growth of the 6.67 GHz methanol maser in G107.298+5.639 was observed during the night September 2/3 by Irbene 16 m radio telescope. A day before the flux densities of two components at VLSR= -8.6 km/s and VLSR= -7.38 km/s were around minimal detection level ~0.8 Jy. During 17 hours both components reached ~ 5 Jy peak flux density. Extensive monitoring campaign (near continuous observation with 40 min intervals) have shown that the current G107.298+5.639 flare is unusually strong: the -7.38 km/s component reached 101 Jy peak flux density (2018 Sept 7, 21:05 UTC ) while all previously reported values did not exceed 60 Jy, the -9.26 km/s component reached 23.5 Jy and stayed close to this level from Sept 7 18:10 UTC  till Sept 8 19:50 UTC, the -8.6 km/s component reached its maximum 11.5 Jy peak flux density on Sept 5, 21:45 UTC. Low intensity components also flared: the -11.01 km/s component peaked with 4.5 Jy (Sept 8, 8:20 UTC), the -15.4 km/s one peaked with 3.4 Jy (Sept 11, 21:20 UTC). The weakest -16.6 km/s component peaked first (Sept 3, 17:00 UTC). According to our observations G107.298+5.639 flare maximums in September and July are 66.4 days apart. This is less than expected from 34.4+/- 0.8 day period estimated by M. Szymczak et al. (2016). This can be a result of the glitch or monotonous period change. If the source experiences monotonous change of the period, the next methanol maser flare should be expected earlier. The maximum of methanol maser was accompanied by the minimum of the water maser emission. On August 23 water maser spectrum of the source contained 3 components at -18.65, -16.5 and -14.6 km/s and these flux densities were equal 240, 730 and 490 Jy respectively. On September 6 only one component at -14.3 km/s had 165 Jy flux density. On September 26 all 3 components come back and these flux densities are equal 240, 660 and 450 Jy respectively. Besides that the component with 77 Jy appears at -9.9 km/s and the component with 40 Jy appears at -7.1 km/s. Observations at Caucassian Mountain Observatory of Moscow state University have shown that in the period of the maximum of methanol emission brightness of the object in K infrared colour was considerably increased.