According to a new scientific paper published in Science, the mystery behind the supra luminous supernova is a galaxy sitting in front, which amplifies its light, like a natural magnifying glass.
As reported in their abstract:
Recently, a supernova was found to shine much brighter than normal for its distance, which resulted in a debate: Was it a new type of superluminous supernova or a normal SNIa magnified by a hidden gravitational lens? Here, we report that a spectrum obtained after the supernova faded away shows the presence of a foreground galaxy—the first found to strongly magnify a SNIa. We discuss how more lensed SNIa can be found than previously predicted.
This galaxy lay hidden between Earth and the supernova – and has now been detected with a telescope in Hawaii.