The Explosion in Orion-KL as Seen by Mosaicking the Magnetic Field with
  ALMA
  We present the first linear-polarization mosaicked observations performed by
the Atacama Large Millimeter/submillimeter Array (ALMA). We mapped the
Orion-KLeinmann-Low (Orion-KL) nebula using super-sampled mosaics at 3.1 and
1.3 mm as part of the ALMA Extension and Optimization of Capabilities (EOC)
program. We derive the magnetic field morphology in the plane of the sky by
assuming that dust grains are aligned with respect to the ambient magnetic
field. At the center of the nebula, we find a quasi-radial magnetic field
pattern that is aligned with the explosive CO outflow up to a radius of
approximately 12 arc-seconds (~ 5000 au), beyond which the pattern smoothly
transitions into a quasi-hourglass shape resembling the morphology seen in
larger-scale observations by the James-Clerk-Maxwell Telescope (JCMT). We
estimate an average magnetic field strength $\langle B\rangle = 9.4$ mG and a
total magnetic energy of 2 x 10^45 ergs, which is three orders of magnitude
less than the energy in the explosive CO outflow. We conclude that the field
has been overwhelmed by the outflow and that a shock is propagating from the
center of the nebula, where the shock front is seen in the magnetic field lines
at a distance of ~ 5000 au from the explosion center.
