Discovery of ammonia (9,6) masers in two high-mass star-forming regions
  Molecular maser lines are signposts of high-mass star formation, probing
excitation and kinematics of very compact regions in the close environment of
young stellar objects and providing useful targets for trigonometric parallax
measurements. Only a few NH$_{3}$ (9,6) masers were known so far, and their
origin is still poorly understood. Here we aim to find new NH$_{3}$ (9,6)
masers to provide a better observational basis to study their role in high-mass
star-forming regions. We carried out NH$_{3}$ (9,6) observations toward Cepheus
A and G34.26$+$0.15 with the Effelsberg-100 m telescope and the Karl G. Janksy
Very Large Array. We discovered new NH$_{3}$ (9,6) masers in Cep A and
G34.26$+$0.15, which increases the number of high-mass star-forming regions
hosting NH$_{3}$ (9,6) masers from five to seven. Long term monitoring (20
months) at Effelsberg shows that the intensity of the (9,6) maser in
G34.26$+$0.15 is decreasing, while the Cep A maser remains stable. Compared to
the Effelsberg data and assuming linear variations between the epochs of
observation, the JVLA data indicate no missing flux. This suggests that the
NH$_3$ (9,6) emission arises from single compact emission regions that are not
resolved by the interferometric measurements. As JVLA imaging shows, the
NH$_{3}$ (9,6) emission in Cep A originates from a sub-arcsecond sized region,
slightly to the west of the peak position of the 1.36\,cm continuum object,
HW2. In G34.26$+$0.15, three NH$_{3}$ (9,6) maser spots are observed: one is
close to the head of the cometary ultracompact \h2 region C and the other two
are emitted from a compact region to the west of the hypercompact \h2 region A.
The newly found (9,6) masers appear to be related to outflows. Higher angular
resolution of JVLA and VLBI observations are needed to provide more accurate
positions and constraints for pumping scenarios.
