We present observations of the possible short GRB 180418A in \gamma -rays , X-rays , and in the optical .
Early optical photometry with the TAROT and RATIR instruments show a bright peak ( \approx 14.2 AB mag ) between T + 28 and T + 90 seconds that we interpret as the signature of a reverse shock .
Later observations can be modeled by a standard forward shock model and show no evidence of a jet break , allowing us to constrain the jet collimation to \theta _ { j } > 7 ^ { \circ } .
Using deep late-time optical observations we place an upper limit of r > 24 AB mag on any underlying host galaxy .
The detection of the afterglow in the Swift UV filters constrains the GRB redshift to z < 1.3 and places an upper bound on the \gamma -ray isotropic equivalent energy E _ { \gamma,iso } < 3 \times 10 ^ { 51 } erg .

The properties of this GRB ( e.g .
duration , hardness ratio , energetic , and environment ) lie at the intersection between short and long bursts , and we can not conclusively identify its type .
We estimate that the probability that it is drawn from the population of short GRBs is 10 % -30 % .