Tentative detection of the gravitational magnification of type Ia supernovae

The flux from distant type Ia supernovae (SN) is likely to be amplified or de-amplified by gravitational lensing due to matter distributions along the line-of-sight. A gravitationally lensed SN would appear brighter or fainter than the average SN at a particular redshift. We estimate the magnification of 26 SNe in the GOODS fields and search for a correlation with the residual magnitudes of the SNe. The residual magnitude, i.e. the difference between observed and average magnitude predicted by the “concordance model” of the Universe, indicates the deviation in flux from the average SN. The linear correlation coefficient for this sample is r = 0.29. For a similar, but uncorrelated sample, the probability of obtaining a correlation coefficient equal to or higher than this value is ∼ 10%, i.e. a tentative detection of lensing at ∼ 90% confidence level. Although the evidence for a correlation is weak, our result is in accordance with what could be expected given the small size of the sample.