  GRB 051103 is considered to be a candidate soft gamma repeater (SGR)
extragalactic giant magnetar flare by virtue of its proximity on the sky to
M81/M82, as well as its time history, localization, and energy spectrum. We
have derived a refined interplanetary network localization for this burst which
reduces the size of the error box by over a factor of two. We examine its time
history for evidence of a periodic component, which would be one signature of
an SGR giant flare, and conclude that this component is neither detected nor
detectable under reasonable assumptions. We analyze the time-resolved energy
spectra of this event with improved time- and energy resolution, and conclude
that although the spectrum is very hard, its temporal evolution at late times
cannot be determined, which further complicates the giant flare association. We
also present new optical observations reaching limiting magnitudes of R > 24.5,
about 4 magnitudes deeper than previously reported. In tandem with
serendipitous observations of M81 taken immediately before and one month after
the burst, these place strong constraints on any rapidly variable sources in
the region of the refined error ellipse proximate to M81. We do not find any
convincing afterglow candidates from either background galaxies or sources in
M81, although within the refined error region we do locate two UV bright star
forming regions which may host SGRs. A supernova remnant (SNR) within the error
ellipse could provide further support for an SGR giant flare association, but
we were unable to identify any SNR within the error ellipse. These data still
do not allow strong constraints on the nature of the GRB 051103 progenitor, and
suggest that candidate extragalactic SGR giant flares will be difficult,
although not impossible, to confirm.
