Detection of the longest periodic variability in 6.7 GHz methanol masers G5.900-0.430

TL;DR

This study reports the detection of two distinct periodic variabilities in 6.7 GHz methanol masers associated with G5.900-0.430, including the longest known period, and discusses possible mechanisms behind these variations.

Contribution

It is the first to identify two different periods in the same source, including the longest known period for 6.7 GHz methanol masers, and links variability patterns to specific physical models.

Findings

Detected ~1260-day period in maser features

Identified a secondary 130.6-day period in a different feature

Proposed pulsation instability and shock models as explanations

Abstract

Long term monitoring observations with the Hitachi 32-m radio telescope of the 6.7 GHz methanol masers associated with the high mass star-forming region G5.900-0.430 is presented. A period of flux variability at approximately 1260 days, is detected in the features at VLSR = 9.77 and 10.84 km/s while a secondary shorter period, 130.6 days, is determined for the 0.66 km/s feature. This is only the second source which has two different periods. The period of ~1260 days is approximately twice as long as the longest known period of 6.7 GHz methanol masers. The variability pattern of the symmetric sine curves and the consistency with the expected period-luminosity relation suggest that the mechanism of maser flux variability of 9.77 and 10.84 km/s features in this source can be explained by protostellar pulsation instability. On the other hand, because the 0.66 km/s feature has an intermittent and asymmetric variability profile, we propose this feature is explained by the CWB or spiral shock models. Obtaining the spatial distribution of the 0.66 km/s feature using an VLBI will lead to a better understanding of this source.