Variability of Water Masers in W49N: Results from Effelsberg Long-term Monitoring Programme

We present the results from an ongoing long-term monitoring of the 22 GHz H₂O maser in W49N with the 100-m Effelsberg radio telescope from February 2014 to September 2017. The unique Effelsbergs spectral line observation capability provides a broad velocity range coverage from -500 to +500 km s^-1 with a spectral resolution better than 0.1 km/s. Following the strong major outburst in W49N in late 2013, we have started a long-term monitoring programme at Effelsberg. The major outburst feature (up to 80,000 Jy at V_LSR - 98 km s^-1) faded away by June 2014. However, we found that the site is still active with several high velocity outbursts (both blue and redshifted). Some features appear at extremely high velocities (up to +/-280 km s^-1) and show rapid flux variations within a 1-2 month period. This sub-year scale variability implies that the water masers could be excited by episodic shock propagation caused by a high-velocity protostellar jet.