Water Masers Diagnosing Postshocked Conditions in W49N
  We present spectroscopic results of 146 water maser outbursts in W49 N, obtained with the Metsahovi radio telescope at 22 GHz. Combining this data with Gwinn's VLBI results, we were able to fix the free parameters in the shock model of Hollenbach and McKee and the maser model of Elitzur, Hollenbach, and McKee. This enabled a straightforward determination of some 20 shock and maser parameters, among others, the kinetic temperature, postshock density, water density, water abundance, preshock and postshock magnetic field strengths as well as the inclination of the mean field with respect to the line of sight. A step-by-step presentation of our diagnostic method is given and the relation between observations and model parameters is discussed. One uniquely powerful outburst feature, referred to as the "big flare feature", showed also the narrowest linewidth. Observations indicate that the velocity of this feature lies in the plane of the sky, whereas preshock and postshock magnetic fields are directed nearly along the line of sight. Consequently, Alfvenic wave fluctuations along the line of sight, and linewidth, are minimal, and a very high aspect ratio is achieved. Furthermore, the big flare feature stands out through its low space velocity, higher temperature (480 K), and larger preshock magnetic field strength (8.2 mG). 
T. Liljestrom and C. R. Gwinn