New Periodic 6.7 GHz Class II Methanol Maser Associated with G358.460-0.391

TL;DR

This study reports the discovery of a new periodic 6.7 GHz class II methanol maser associated with G358.460-0.391, exhibiting a stable 220-day cycle, based on three years of multi-frequency radio observations.

Contribution

First detection of a periodic 6.7 GHz methanol maser in G358.460-0.391, with detailed analysis confirming its 220-day cycle using multiple statistical methods.

Findings

Discovered a 220-day periodicity in the maser emission.

Monitored maser variability over three years.

Identified the source as a new periodic methanol maser.

Abstract

Eight new class II methanol masers selected from the 6.7 GHz Methanol Multibeam survey catalogues I and II were monitored at 6.7 GHz with the 26m Hartebeesthoek Radio Astronomy Observatory (HartRAO) radio telescope for three years and seven months, from February 2011 to September 2014. The sources were also observed at 12.2 GHz and two were sufficiently bright to permit monitoring. One of the eight sources, namely G358.460-0.391, was found to show periodic variations at 6.7 GHz. The period was determined and tested for significance using the Lomb-Scargle, epoch-folding and Jurkevich methods, and by fitting a simple analytic function. The best estimate for the period of the 6.7 GHz class II methanol maser line associated with G358.460-0.391 is 220.0 $\pm$ 0.2 day.