Description of source "G333.13-0.44" from Voronkov et al. (2014)

This is the only target in our sample which contains four 6.7-GHz methanol masers: a close pair of weak masers (333.126−0.440 and 333.128−0.440, separated by 7 arcsec, both weaker than several Jy) near the centre of the image shown in Fig. 1, 333.121−0.434 in the west and another weak maser, 333.135−0.431, in the north (Caswell 1997; Caswell et al. 2011b). The distribution of class I maser emission suggests rather straightforward identification of each class I maser site with a particular 6.7-GHz maser. However, it must be noted that ambiguity cannot be completely excluded for class I masers corresponding to the close pair of the 6.7-GHz masers. The dominant infrared source in Fig. 1 is associated with the south-western 6.7-GHz maser of the pair, 333.126−0.440. The class I masers at A are at the position of the 6.7-GHz maser within the measurement uncertainty and scattered within several arcsec of it. Note that decomposition of the spectral profile into the Gaussian components leaves systematic residuals near minima between individual peaks. The effect is seen at both frequencies, but is much more pronounced at 44 GHz. The class I maser at C is located 20 arcsec south of A and may be an unrelated source. The profile looks very similar to the peak of A, but is too strong to be an artefact. The north-eastern 6.7-GHz maser of the pair, 333.128−0.440, is located near an infrared source (showing 3.6-µm excess), but in an area devoid of extended infrared emission in the Spitzer overlay (Fig. 1). The associated class I masers (locations D–F and H) are spread around 10 × 10 arcsec2 area to the north-east, further away from the pair of 6.7-GHz masers. All this class I maser emission is blueshifted with respect to the associated 6.7-GHz maser. The northern 6.7-GHz maser, 333.135−0.431 is associated with the continuum source and an extended infrared source which appears green in the three-colour map (Fig. 1) suggesting an excess at 4.5 µm. However, this source is not listed as an EGO by Cyganowski et al. (2008). Unlike the other three sites, this one harbours an OH maser (Caswell 1998). The class I methanol masers at G (only 44-GHz masers are detected) are located nearby, but appear not to be directly associated with the infrared source (about 10 arcsec offset from the 6.7-GHz maser). The 44-GHz maser is blueshifted with respect to the northern 6.7-GHz maser. This location is beyond the half-power point of the primary beam at 44 GHz. Therefore, additional class I masers related to the same YSO could have been missed. The western 6.7-GHz maser, 333.121−0.434, is related to the class I masers at B located within a few arcsec from it towards a north-western direction. At a comparable offset in the south-eastern direction lies a weak continuum source which may represent a working surface of an outflow. This site (B) is located near the edge of a dark cloud (Peretto & Fuller 2009) with the rim traced by a long 8.0-µm filament. Mottram et al. (2007) also reported a radio-continuum emission extending from a prominent H II region at the northern edge of Fig. 1 along the filament towards B (see also Urquhart et al. 2007). Although we cannot exclude that the class I masers at B are directly associated with the 8.0-µm filament, most likely they are related to an outflow in a separate high-mass star-forming region whose formation has been triggered by interaction of the dark cloud with its surroundings.