Most powerful maser in the Galaxy is source G25.65+1.05 and the most powerful emitter in the Universe AGN S 0528+134.

Several powerful flare events have been recorded because of long-term monitoring on the RT-22 radio telescope (Simeiz) of the galactic source G25.65 + 1.05 from 2000 to 2024. The amplitude of the most powerful flare increased rapidly and reached a record level for this source of 130 kJy. The orbital (7.5 years) and precessional (60 years) periods in the binary system of massive O5 class stars responsible for the occurrence of flares based on monitoring data have been presumably determined. Individual short flares, lasting no more than a month, presumably belonged to a maser in an unsaturated state. The shape of the central part of the maser line, near the maximum phase, suggests a single-component source responsible for the bulk of the increase in flux density. Thus, the most powerful kilomaser G25.65 + 1.05 in the water vapor line at frequency 22.2 GHz has been registered in the Galaxy. The possibility of detecting gravitational waves (GWs) coming from the massive stellar binary system is considered. The active galactic nucleus S 0528 + 134 was discovered in a search survey at a frequency of 8550 MHz in 1969 using the radio telescope RT-22 (Simeiz) at the Crimean Astrophysical Observatory—the study aimed to search for new active galactic nuclei (AGN). In this article, the goal was to determine the physical characteristics of the close binary system S 0528 + 134 for the subsequent assessment of the level of gravitational radiation coming from it. During long-term monitoring of the object at a frequency of 8 GHz, some powerful flares of flux density occurred, which made it possible to consider the source the most powerful emitter in the Universe. The presence of selected harmonic components in the flux density variations of S 0528 + 134 allowed obtaining the main physical characteristics of a binary system of supermassive black holes (SMBHs), which placed S 0528 + 134 in the rank of one of the most massive SMBHs. This AGN can also be considered the most powerful source for detecting GWs by using International Pulsar Timing Array gravitational wave detectors. [ABSTRACT FROM AUTHOR]