The brightest OH maser in the sky: a flare of emission in W75 N

Abstract

A flare of maser radio emission in the OH-line 1665 MHz has been discovered in the star forming region W75 N in 2003, with the flux density of about 1000 Jy. At the time it was the strongest OH maser detected during the whole history of observations since the discovery of cosmic masers in 1965. The flare emission is linearly polarized with a degree of polarization near 100%. A weaker flare with a flux of 145 Jy was observed in this source in 2000 - 2001, which was probably a precursor of the powerful flare. Intensity of two other spectral features has decreased after beginning of the flare. Such variation of the intensity of maser condensation emission (increasing of one and decreasing of the other) can be explained by passing of the magneto hydrodynamic shock across regions of enhanced gas concentration.