Discovery of four periodic methanol masers and updated light curve for a further one

Abstract

We report the discovery of 6.7 GHz methanol maser periodic flares in four massive star forming regions and the updated light curve for the known periodic source G22.357+0.066. The observations were carried out with the Torun 32 m radio telescope between June 2009 and April 2014. Flux density variations with period of 120 to 245 d were detected for some or all spectral features. A variability pattern with a fast rise and relatively slow fall on time-scale of 30−60 d dominated. A reverse pattern was observed for some features of G22.357+0.066, while sinusoidal-like variations were detected in G25.411+0.105. A weak burst lasting ∼520 d with the velocity drift of 0.24 km s −1 yr −1 occurred in G22.357+0.066. For three sources for which high resolution maps are available, we found that the features with periodic behaviour are separated by more than 500 au from those without any periodicity. This suggests that the maser flares are not triggered by large-scale homogeneous variations in either the background seed photon flux or the luminosity of the exciting source and a mechanism which is able to produce local changes in the pumping conditions is required.

Discovery of periodic class II methanol masers associated with G339.986−0.425 region

“…The discovery of periodic variability in the 6.7-and 12.2-GHz methanol masers reported by Goedhart et al (2003Goedhart et al ( , 2004Goedhart et al ( , 2009Goedhart et al ( , 2013) was unexpected as it had not been previously reported in any maser transitions associated with high-mass star formation regions. Further monitoring programmes have been conducted independently and confirmed the existence of periodic variations in eight more methanol masers (Araya et al 2010;Szymczak et al 2011Szymczak et al , 2015Fujiswa et al 2014;Maswanganye et al 2015), bringing the total number of periodic masers to 15.…”

The 6-GHz methanol multibeam maser catalogue – V. Galactic longitudes 20°–60°

“…Wu et al (2014) Szymczak et al (2015) have recently shown that spectral feature at 59.6 km s −1 exhibits a periodicity of 195.7 d, finding that it has a stable flux density state of 1.3-1.4 Jy and a flare flux density of 3.6-8.6 Jy. In our observations, this spectral feature has a flux density of 1.3 Jy, indicating that the source was in the quiescent state at the time.…”

“…Moscadelli et al (2007) present a thorough study of this star formation region, with observations of the 1665-MHz OH, 22-GHz water, 44-and G 25.411+0.105. Using monitoring data from the Torun telescope, Szymczak et al (2015) found that this source exhibits periodic fluctuations in flux density. EVN observations of this maser have revealed a ring-like morphology of maser spots (Bartkiewicz et al 2009).…”

Periodic methanol masers in G9.62+0.20E

“…On the other hand, based on the results of a high-resolution astrometric study of CH 3 OH, H 2 O, and OH masers, as well as 7 mm continuum emission of G9.62+0.20E, Sanna et al (2015) suggest that the periodic masers in this source can be accounted for by the presence of an independent pulsating young massive star within the context as proposed by Inayoshi et al (2013). In addition to these two papers, Szymczak et al (2015) recently presented the discovery of four new periodic masers and an updated light curve for G22.357+0.066 which is strikingly similar to that of the 12.2 GHz masers in G9.62+0.20E. These authors argue that although the colliding-wind binary (CWB) model of van der Walt (2011) can explain the flare profile of G22.357+0.066, models in which the maser flares are related to changes in the maser optical depths and excitation temperatures -such as that of Inayoshi et al (2013) and Parfenov & Sobolev (2014) -are preferred to the CWB explanation.…”