New Maser Emission from Nonmetastable Ammonia in NGC 7538. IV.
  Coincident Masers in Adjacent States of Para-ammonia
  We present the first detection of para-ammonia masers in NGC 7538: multiple
epochs of observation of the 14NH3 (J,K) = (10,8) and (9,8) lines. We detect
both thermal absorption and nonthermal emission in the (10,8) and (9,8)
transitions and the absence of a maser in the (11,8) transition. The (9,8)
maser is observed to increase in intensity by 40% over six months. Using
interferometric observations with a synthesized beam of 0.25", we find that the
(10,8) and (9,8) masers originate at the same sky position near IRS1. With
strong evidence that the (10,8) and (9,8) masers arise in the same volume, we
discuss the application of pumping models for the simultaneous excitation of
nonmetastable (J > K) para-ammonia states having the same value of K and
consecutive values of J. We also present detections of thermal absorption in
rotational states ranging in energy from E/k_B ~ 200 K to 2000 K, and several
non-detections in higher-energy states. In particular, we describe the
populations in eight adjacent rotational states with K=6, including two maser
transitions, along with the implications for ortho-ammonia pumping models. An
existing torus model for molecular gas in the environment of IRS1 has been
applied to the masers; a variety of maser species are shown to agree with the
model. Historical and new interferometric observations of 15NH3 (3,3) masers in
the region indicate a precession of the rotating torus at a rate comparable to
continuum-emission-based models of the region. We discuss the general necessity
of interferometric observations for diagnosing the excitation state of the
masers and for determining the geometry of the molecular environment.
