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We analyze images of the CFHTLS Very Wide Survey to search for visible orphanafterglows from gamma-ray bursts (GRBs). We have searched 490 square degreesdown to magnitude r'=22.5 for visible transients similar to GRB afterglows. Wetranslate our observations into constraints on the number of GRB visibleafterglows in the sky, by measuring the detection efficiency of our search witha simulation reproducing the characteristics of our observational strategy andthe properties of on-axis GRB afterglows. We have found only three potentialcandidates, of which two are most probably variable stars, and one presentssimilarities to an orphan afterglow. We constrain the number of visibleafterglows to be less than 220 down to r'=22.5 in the whole sky at any time.Our observations are marginally consistent with the most optimistic model,which predicts orphan afterglows to be about 10 times more frequent than GRBs.This search has led to the detection of one possible GRB afterglow, andprovides the strongest constraints on the rate of GRB visible afterglows aswell as an estimation of the observing time required to detect a significantnumber of GRB afterglows.Comment: 4 pages, 3 figures, 2 tables. Accepted by A&A Lette

Constraining the rate of GRB visible afterglows with the CFHTLS very wide survey