Discovery of synchronized periodic variability of methanol maser features in G26.598–0.024

¹ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun, Poland
² Department of Mathematical Sciences, University of South Africa, Cnr Christian de Wet Rd and Pioneer Avenue, Florida Park, 1709 Roodepoort, South Africa
³ Department of Physics and Astronomy, Faculty of Physical Sciences, University of Nigeria, Carver Building, 1 University Road, Nsukka 410001, Nigeria
⁴ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany

^★ Corresponding author: wolak@astro.umk.pl

Received: 16 June 2025
Accepted: 18 July 2025

Abstract

Aims. We report the discovery of periodic maser variability of an unusual pattern in the high-mass young stellar object G26.598–0.024.

Methods. A ten-year monitoring of the 6.7 GHz methanol maser was carried out with the Torun 32 m radio telescope. The archival data collected so far were also used to characterize the target with high angular resolution and examine its infrared variability.

Results. We found anticorrelated flux variations of the opposite blueshifted and redshifted emission features with a period of 70.1±2.2 d and the relative amplitude of 1.3 and 0.6, respectively. The light curves are best fit with a sinusoidal function modulated by mild changes in the average flux density on 3–5 yr timescales. The emission of the middle parts of the spectrum shows only long-term variability. High-angular-resolution data indicate that the maser is associated with one of the two 1.3 mm dust emission cores, while the periodic emission comes from two extended regions ~1500 au apart. We discuss several possible causes of the peculiar variability.