  We use the HST ACS imaging of the two GOODS fields during Cycles 11, 12, and
13 to derive the Type Ia supernova rate in four redshift intervals in the range
0.2<z<1.8. Compared to our previous results based on Cycle 11 observations
only, we have increased the coverage of the search by a factor 2.7, making the
total area searched equivalent to one square degree. The sample now consists of
56 Type Ia supernovae. The rates we derive are consistent with our results
based on the Cycle 11 observations. In particular, the few detected supernovae
at z>1.4 supports our previous result that there is a drop in the Type Ia
supernova rate at high redshift, suggesting a long time delay between the
formation of the progenitor star and the explosion of the supernova. If
described by a simple one-parameter model, we find a characteristic delay time
of 2-3 Gyr. However, a number of recent results based on e.g., low redshift
supernova samples and supernova host galaxy properties suggest that the
supernova delay time distribution is bimodal. In this model, a major fraction
of the Type Ia supernova rate is 'prompt' and follows the star formation rate,
while a smaller fraction of the rate has a long delay time, making this channel
proportional to mass. While our results are fully consistent with the bimodal
model at low redshifts, the low rate we find at z>1.4 appears to contradict
these results. Models that corrects for star formation hidden by dust may
explain at least part of the differences. Here we discuss this possibility
together with other ways to reconcile data and models.
