Shock-heated NH3 in a molecular jet associated with a high-mass young star

We present the discovery of shock-excited NH3 in a well-collimated jet asso ciated with the extremely young high-mass star IRAS 20126+4104. The NH3 (3, 3) and (4, 4) emission is dominated by three clumps along the SiO jet. At the end of the jet, there exists strong and broad (+/-10 km s(-1)) NH3 (3, 3) emission. With typical brightness temperatures greater than 500 K, the o verall emission indicates a weakly inverted population and appears in an ar e, consistent with the excitation by bow shocks. There are two bright spots in the NH3 (3, 3) emission with brightness temperatures of approximately 2 000 K. The narrow line width (1.5 km s(-1) FWHM), the small sizes (<0 ".3), and the unusually high brightness temperature of the features are indicati ve of maser emission. Our observations provide clear evidence that NH3 (3, 3) masers are excited in shack regions in molecular outflows.