6.7 GHz methanol maser variability in Cepheus A

Abstract

6.7 GHz methanol maser emission from the well-studied star-forming region Cepheus A was monitored with the Torun 32 m radio telescope. We found synchronized and anticorrelated changes of the flux density of the two blueshifted and one redshifted maser features for ∼30 per cent of 1340 d of our observations. Two of those features exhibited high amplitude flux density variations with periods of 84−87 d over the last 290 d interval of the monitoring. We also report on two flares of emission at two different redshifted velocities completely covered during the whole outburst. These flare events lasted 510−670 d and showed a very rapid linear rise and slow exponential decline, which may be caused by variability of the seed flux density. The flux density of the two strongest features dropped by a factor of 2−5 on a time-scale ∼22 yr, while other features have not changed significantly during this period, but showed strong variability on time-scales 5 yr.

On the Class II methanol maser periodic variability due to the rotating spiral shocks in the gaps of discs around young binary stars

“…However, number of indications on that increases. For example, periodic variability was recently found in Cepheus A by Szymczak et al (2014). The Class II methanol masers in this source most probably reside in the ring that is perpendicular to the jet associated with the radio continuum source HW2 (Torstensson et al 2011).…”

New evidence for Dicke’s superradiance in the 6.7 GHz methanol spectral line in the interstellar medium

“…Menten (1991 first reported the detection of the 6.7 GHz line in this source with a flux density of 1420 Jy at −6 km s −1 < v lsr < −1 km s −1 . The strongest feature at v lsr = −2.1 km s −1 subsequently dropped in flux density from 1420 Jy to 815 Jy over a timespan of 8.1 year (Szymczak, Wolak & Bartkiewicz 2014). Followup observations by Sugiyama et al (2008b) identified five spectral features, where the redshifted components at -1.9 and −2.7 km s −1 showed 50% decrease in flux over 81 days.…”

“…The molecular outflow associated with HW2 shows a complex morphology with high-velocity (v > 500 km s −1 ) ionized jet and a slow (v = 10−70 km s −1 ) wide-angle outflow (Torrelles et al 2011). Szymczak et al (2014) monitored 6.7 GHz methanol masers in Cep A HW2 with the Torun 32 m telescope for a period of 1340 days. They also found synchronized and anticorrelated flux density variations between two blueshifted and one redshifted features over 30% of their observation period.…”

Long-term multi-frequency maser observations of the intermediate-mass young stellar object G107.298+5.639

“…For methanol the system temperature ranged from 25 K to 30 K. The HPBW was 5 and the pointing accuracy was better than ∼25 before mid-2016 and ∼10 afterwards. The data were calibrated by regular scans on the continuum source 3C123 and daily observations of the methanol maser G32.744−0.076, in which some features are non-variable within 5% (Szymczak et al 2014). The typical r.m.s noise level in the final methanol spectra of 0.09 km s −1 resolution was about 0.3 Jy.…”