Discovery of the new class I methanol maser transition at 23.4 GHz

Abstract

We report the first detection of a methanol maser in the 10(1)-9(2)A- transition at 23.4 GHz, discovered during the H2O southern Galactic Plane Survey (HOPS) with the 22-m Mopra radio telescope. In the region covered by HOPS, the 23.4 GHz maser was found at only one location, G357.97-0.16, which was also a prominent source of maser emission in the J(2)-J(1)E series near 25 GHz. The Australia Telescope Compact Array (ATCA) was used to follow up these detections at high angular resolution and prove the maser nature of the observed emission. The analysis shows that the new methanol maser at 23.4 GHz is a class I maser, which has properties similar to the 9.9 and 25 GHz masers (i.e. traces strong shocks with higher than average temperature and density). All class I masers were found to originate at the same spatial location (within the measurement uncertainty of 0.5 arcseconds) in the vicinity of the dominant infrared source, but at a clearly distinct position from nearby OH, H2O and class II methanol masers at 6.7 GHz. All maser species are distributed approximately on a line, but it is not clear at present whether this has any physical significance. We also detected a weak (1.3 mJy) continuum source at 25 GHz near the OH maser (at the most northern site, associated with a class II methanol maser and an H2O maser renowned for its extremely wide spread of velocity components). The continuum source has not been reported at lower frequencies and is therefore a candidate hypercompact HII region. We also used the ATCA to find the strongest and only fifth known 9.9 GHz maser towards G357.97-0.16 and another 23.4 GHz maser towards G343.12-0.06 not seen in HOPS.

7 pages, 2 figures, 2 tables, accepted by MNRAS

References in corpus (3)

• A Class I and Class II Methanol Maser Survey of Extended Green Objects (EGOs) from the GLIMPSE Survey
• Class I methanol masers in the outflow of IRAS 16547-4247
• A Pilot Survey for the H${}_2$O Southern Galactic Plane Survey (HOPS)

Cited by in corpus (15)

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• Methanol as a tracer of fundamental constants
• Physical characteristics of bright Class I methanol masers
• Online Database of Class I Methanol Masers
• 12.2-GHz methanol maser MMB follow-up catalogue - I. Longitude range 330 to 10 degrees
• A 95 GHz Class I Methanol Maser Survey Toward A Sample of GLIMPSE Point Sources Associated with BGPS Clumps
• A search for water masers associated with class II methanol masers - II. Longitude range 341${}^{\circ }$ to 6${}^{\circ }$
• A search for 95 GHz class I methanol masers in molecular outflows
• 84-GHz methanol masers, their relationship to 36-GHz methanol masers and their molecular environments
• Methanol Observation of IRAS 19312+1950: A Possible New Type of Class I Methanol Masers
• Molecular line search toward the flaring 6.7-GHz methanol masers of G24.33+0.13 and G359.6-0.243: rare maser transitions detected
• New class I methanol masers
• Redshifted methanol absorption tracing infall motions of high-mass star formation regions
• Masers in star forming regions