  We observed the J=9-8 and 10-9 rotational lines of three13C isotopologues of
HC3N in L1527 and G28.28-0.36 with the 45-m radio telescope of the Nobeyama
Radio Observatory in order to constrain the main formation mechanisms of HC3N
in each source. The abundance ratios of the three 13C isotopologues of HC3N are
found to be 0.9 (0.2) : 1.00 : 1.29 (0.19) (1sigma) and 1.0 (0.2) : 1.00 : 1.47
(0.17) (1sigma) for [H13CCCN]: [HC13CCN]: [HCC13CN] in L1527 and G28.28-0.36,
respectively. We recognize a similar 13C isotopic fractionation pattern that
the abundances of H13CCCN and HC13CCN are comparable, and HCC13CN is more
abundant than the others. Based on the results, we discuss the main formation
pathway of HC3N. The 13C isotopic fractionation pattern derived from our
observations can be explained by the neutral-neutral reaction between C2H2 and
CN in both the low-mass (L1527) and high-mass (28.28-0.36) star forming
regions.
