A multi-transition methanol maser study of the accretion burst source
  G358.93-0.03-MM1
  We present the most complete to date interferometric study of the centimeter
wavelength methanol masers detected in G358.93-0.03 at the burst and post-burst
epochs. A unique, NIR/(sub)mm-dark and FIR-loud MYSO accretion burst was
recently discovered in G358.93-0.03. The event was accompanied by flares of an
unprecedented number of rare methanol maser transitions. The first images of
three of the newly-discovered methanol masers at 6.18, 12.23, and 20.97 GHz are
presented in this work. The spatial structure evolution of the methanol masers
at 6.67, 12.18, and 23.12 GHz is studied at two epochs. The maser emission in
all detected transitions resides in a region of $\sim$0.2$^{\prime\prime}$
around the bursting source and shows a clear velocity gradient in the
north-south direction, with red-shifted features to the north and blue-shifted
features to the south. A drastic change in the spatial morphology of the masing
region is found: a dense and compact "spiral" cluster detected at epoch I
evolved into a disperse, "round" structure at epoch II. During the transition
from the first epoch to the second, the region traced by masers expanded. The
comparison of our results with the complementary VLA, VLBI, SMA, and ALMA maser
data is conducted. The obtained methanol maser data support the hypothesis of
the presence of spiral-arm structures within the accretion disk, which was
suggested in previous studies of the source.
