6.7 GHz methanol maser flare in high-mass protostar G85.410+0.003

ATel #17227; Ross A. Burns (RIKEN), Janis Steinbergs, Artis Aberfelds, Karina Skirmante, Vladislavs Bezrukovs, Ivars Smelds (ERI VIRAC of VUAS), Yoshihiro Tanabe (Yamaguchi University), Yoshinori Yonekura (Ibaraki University)
on 11 Jun 2025; 11:01 UT
Credential Certification: Ross Burns (ross.burns@riken.jp)

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A modest flare of the 6.7 GHz methanol maser has been identified toward high-mass protostar G85.410+0.003. The maser spectrum of G85.410+0.003 exhibits two main components; one at a velocity of -31.5 km/s and another at -29.5 km/s, with some low-brightness emission also seen between and around the two main peaks. The -31.5 km/s methanol maser feature exhibited a flare in October 2019, rising from around 10 Jy to around 125 Jy. New flaring activity began sometime around October 2024 in the other main feature at -29.5 km/s, rising from 50 Jy to around 150 Jy, before retracing back to around 50 Jy in the present day (Fig. 1.). The 5 year difference in the timing of flares is more similar to previous examples of repeating methanol maser flares (such as the case G24.33+0.14, ATel #13080) rather than a single excitation event inducing staggered flaring in a collection of velocity features (such as the case of G358.93-0.03, ATel #12446).

At the time of writing there also appears to be new activity in the low brightness emission in the region of the spectrum between the two main peaks. The flux density of the -30.7 km/s component (red coloured data in Fig 1.) was < 10 Jy before MJD 60797 (2025 May 02), which gradually increased to 35.6 Jy at MJD 60822 (2025 May 27), (Fig. 2.) and is now decreasing (26.5 Jy as of 60835 [2025 June 09]). It is therefore apparent that the activity in G85.410+0.003 during this event is not isolated to a single velocity feature and merits further investigation.

The flare was initially identified using the Irbene single-baseline interferometer which is capable of monitoring both maser and radio continuum emission in high-mass protostars. During the period of activity in the maser emission the 5 cm continuum emission seemed to increase from 39 mJy on 2024 October 16, to 44 mJy on 2024 November 23 (Fig. 3.). However, this measurement is tentative and requires further confirmation. Corroboration of the maser flare was provided by the iMet monitoring team (see also ATel #15680, ATel #16303) using the 32m Hitachi radio telescope who also provided Figures 1 and 2 via the Maser Monitoring Organisation (M2O).

The coordinates of the methanol maser are RA, DEC: 20:54:13.689, +44:54:07.686. We encourage further maser monitoring and follow-up observations of this ongoing flare event to determine its nature.

Ibaraki 6.7 GHz class II methanol maser database (iMet)