• DOI:10.1111/j.1365-2966.2011.18297.x
• Corpus ID: 119117031

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

@article{Voronkov2011DiscoveryOT,
  title={Discovery of the new class I methanol maser transition at 23.4 GHz},
  author={Maxim A. Voronkov and Andrew J. Walsh and James L. Caswell and Simon P. Ellingsen and Shari L. Breen and Steven N. Longmore and Cormac R. Purcell and James S. Urquhart},
  journal={Monthly Notices of the Royal Astronomical Society},
  year={2011},
  volume={413},
  pages={2339-2344}
}

• M. Voronkov, A. Walsh, +5 authors J. Urquhart
• Published 5 January 2011
• Physics
• Monthly Notices of the Royal Astronomical Society

We report the first detection of a methanol maser in the 101–92 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
J2–J1 E series near 25 GHz. The Australia Telescope Compact Array (ATCA) was used to
followup 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 arcsec) 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 the 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.