Originally Posted by Patat et al.

A direct method for investigating the nature of the progenitor systems of Type Ia supernovae (hereafter SNe Ia) is to search for signatures of the material transferred to the accreting white dwarf in the circumstellar material (CSM). Previous attempts have aimed at detecting the radiation which would arise from the interaction between the fast moving SN ejecta and the slow moving CSM in the form of narrow emission lines, radio and X-ray emission. The most stringent upper limit to the mass loss rate set by radio observations is as low as 3x10^8 solar masses per year for an assumed wind velocity of 10 km s^-1.

Two remarkable exceptions are represented by two peculiar SNe Ia, SN 2002ic and SN 2005gj, which have shown extremely pronounced hydrogen emission lines, that have been interpreted as a sign of strong ejecta-CSM interaction. However, the classification of these supernovae as SNe Ia has recently been questioned, and even if they were SN Ia, they are unlikely to account for normal Type Ia explosions that, so far, lack any signature of mass transfer from a hypothetical donor. Here, we report direct evidence of CSM in a SN Ia that has shown a normal behavior at X-ray, optical and radio wavelengths.