  Since the advent of the Swift satellite it has been possible to obtain
precise localisations of GRB positions of sub-arcsec accuracy within seconds,
facilitating ground-based robotic telescopes to automatically slew to the
target within seconds. This has yielded a plethora of observational data for
the afterglow phase of the GRB, but the quantity of data (<2 keV) covering the
initial prompt emission still remains small. Only in a handful of cases has it
been possible obtain simultaneous coverage of the prompt emission in a
multi-wavelength regime (gamma-ray to optical), as a result of: observing the
field by chance prior to the GRB (e.g. 080319B/naked-eye burst), long-prompt
emission (e.g., 080928, 110205A) or triggered on a pre-cursor (e.g., 041219A,
050820A, 061121). This small selection of bursts have shown both correlated and
uncorrelated gamma-ray and optical light curve behaviour, and the
multi-wavelength emission mechanism remains far from resolved (i.e. single
population synchrotron self-Component, electron distributions, additional
neutron components or residual collisions). Such multi-wavelength observations
during the GRB prompt phase are pivotal in providing further insight on the
poorly understood prompt emission mechanism. We add to this small sample the
Swift burst 121217A that had two distinct periods of prompt emission separated
by ~700 s, observed by Swift/BAT, Swift/XRT and Fermi/GBM. As a result of the
time delay of the second emission, it enabled optical imaging (from 3 to 7
bands) to be taken with the GROND instrument to a resolution as fine as 10s.
This multi-wavelength data will hopefully allow us to shed more light on the
current picture of prompt emission physics.
