In a paper led by Yi Cao, we have a new exciting result! An early glimpse of ultraviolet light from a Type Ia supernova, iPTF14atg, reveals what appears to be a shocked neighboring star.
Type Ia supernovae, are produced when white dwarfs, faint stars that have run out of fuel, explode with ferocious intensity. They were used as accurate distance estimators to measure the accelerated rate of expansion of the Universe, awarded the Nobel Prize in 2011. Although thousands of Type Ia supernovae were found in the last decades, the process by which a white dwarf turns explosive has been unclear. This lack of understanding has often been raised as a source of distrust in the use of Type Ia supernovae for high precision cosmology in the future.
However, there are two main hypothesized avenues for how explosions could arise from white dwarfs. A thermonuclear runaway explosion could ignite from either a merger of two white dwarfs or, by transfer of mass from a large neighboring star until the total accreted mass approaches the Chandrasekhar instability limit.
It has been theorized that the telltale signature of the presence of a large donor star would be an ultraviolet pulse preceding the main rise of the supernova light curve. This added flux is thought to be the result of collision of the supernova ejecta with its companion star. The energy released from this shock peaks at short wavelengths, X-rays and UV.
It appears that is what we see in iPTF14atg for the first time, using the Swift satellite triggered soon after the SN was discovered by iPTF. Although very exciting, it is not yet clear if this detection solves the mystery of the SN Ia progenitors, especially since iPTF14atg turned out to be less luminous at optical wavelengths than what expected for a “standard candle” supernova.
The work was led by Caltech PhD student Yi Cao, with contributions from Oskar Klein Centre researchers Joel Johansson, Rahman Amanullah and Ariel Goobar (Fysikum) and Jesper Sollerman and Francesco Taddia (Astronomy).