The Extraordinary Outburst in the Massive Protostellar System
  NGC6334I-MM1: Emergence of Strong 6.7 GHz Methanol Masers
  We report the first sub-arcsecond VLA imaging of 6 GHz continuum, methanol
maser, and excited-state hydroxyl maser emission toward the massive
protostellar cluster NGC6334I following the recent 2015 outburst in
(sub)millimeter continuum toward MM1, the strongest (sub)millimeter source in
the protocluster. In addition to detections toward the previously known 6.7 GHz
Class II methanol maser sites in the hot core MM2 and the UCHII region MM3
(NGC6334F), we find new maser features toward several components of MM1, along
with weaker features $\sim1''$ north, west, and southwest of MM1, and toward
the non-thermal radio continuum source CM2. None of these areas have heretofore
exhibited Class II methanol maser emission in three decades of observations.
The strongest MM1 masers trace a dust cavity, while no masers are seen toward
the strongest dust sources MM1A, 1B and 1D. The locations of the masers are
consistent with a combination of increased radiative pumping due to elevated
dust grain temperature following the outburst, the presence of infrared photon
propagation cavities, and the presence of high methanol column densities as
indicated by ALMA images of thermal transitions. The non-thermal radio emission
source CM2 ($2''$ north of MM1) also exhibits new maser emission from the
excited 6.035 and 6.030 GHz OH lines. Using the Zeeman effect, we measure a
line-of-sight magnetic field of +0.5 to +3.7 mG toward CM2. In agreement with
previous studies, we also detect numerous methanol and excited OH maser spots
toward the UCHII region MM3, with predominantly negative line-of-sight magnetic
field strengths of -2 to -5 mG and an intriguing south-north field reversal.
