  In recent years, many questions have arisen regarding the chemistry of
photochemical products in the carbon-rich winds of evolved stars. To address
them, it is imperative to constrain the distributions of such species through
high angular resolution interferometric observations covering multiple
rotational transitions. We used archival ALMA observations to map rotational
lines involving high energy levels of cyanoacetylene (HC$_3$N) toward the inner
envelope (radius <8"/1000 AU) of the carbon star IRC+10216. The observed lines
include the J=28-27, J=30-29, and J=38-37, transitions of HC$_3$N in its ground
vibrational state. In contrast to previous observations of linear carbon chains
toward this AGB star which show extended, hollow emission at 15"-20" radii
(e.g. C$_4$H, C$_6$H, HC$_5$N), the maps of the HC$_3$N lines here show compact
morphologies comprising various arcs and density enhancements, with significant
emission from gas clumps at an angular distance of ~3" (350 AU) from the
central AGB star. We compared visibility sampled non-LTE radiative transfer
models with the observed brightness distributions, and derive a fractional
abundance with respect to H$_2$ of $10^{-8}$ for HC$_3$N at the radii probed by
these lines. These results are consistent with enhanced photochemistry
occurring in warm (~200 K) regions of the circumstellar envelope. After
application of a specialized chemical model for IRC+10216, we find evidence
that the enhanced HC$_3$N abundances in the inner wind are most likely due to a
solar-type binary companion initiating photochemistry in this region.
