A Water-Vapor Maser Flare in a High-Velocity Line toward W49N

Abstract

Powerful flares in Galactic kilomasers are closely associated with regions of intense star formation. They contribute to the elucidation of physical processes occurring in these structures. We have recorded a superpowerful flare in the high-velocity -81 km/s line in the Galactic maser source W49N. As a result of our monitoring at the RT-22 (Simeiz), RT-32 (Torun), RT-100 (Effelsberg), and RT-32 (Medicina) radio telescopes in the period from September 2017 to November 2018, we have obtained the shape of the spectral flux density variations in the source with time. At the peak the flux density reached P≈5 ×10^4 Jy. The flare has a double pattern and different durations of its components. The pattern of spectral flux density variations for the first flare with a considerably shorter duration is apparently related to a sharp increase in the density of the medium and the photon flux and to a significant rise in the temperature to hundreds of kelvins. We propose a mechanism of primary energy release related to the existence of close massive multiple systems in star-forming regions. A powerful gravitational perturbation at the system's periastron can lead to a partial ejection of the envelope of the central massive star in a direction close to the major axis of the ellipse of the companion's orbit. This explains the significant asymmetry of high-velocity lines in W49N. The ejected envelope is an energy source more significant than the stellar wind and can explain the giant flares in the object. Further comprehensive studies in this direction, including monitoring VLBI studies, are needed to confirm this assumption.