A radio source that faded over six days , with a redshift of z \approx 0.5 host , has been identified by Keane et al .
( 15 ) as the transient afterglow to a fast radio burst ( FRB 150418 ) .
We report follow-up radio and optical observations of the afterglow candidate and find a source that is consistent with an active galactic nucleus .
If the afterglow candidate is nonetheless a prototypical FRB afterglow , existing slow-transient surveys limit the fraction of FRBs that produce afterglows to 0.25 for afterglows with fractional variation , m = 2 |S _ { 1 } - S _ { 2 } | / ( S _ { 1 } + S _ { 2 } ) \geq 0.7 , and 0.07 for m \geq 1 , at 95 % confidence .
In anticipation of a barrage of bursts expected from future FRB surveys , we provide a simple framework for statistical association of FRBs with afterglows .
Our framework properly accounts for statistical uncertainties , and ensures consistency with limits set by slow-transient surveys .