Old supernovae, new insights!

It’s been a long time since my last post (changing jobs/continents is time-consuming!) but I have two almost-new papers I’ve been meaning to share: one recently published in ApJ letters, and the other just accepted in ApJ. The two are linked by the theme of very late-time observations of superluminous supernovae.

hst
Hubble Space Telescope images of SN 2015bn up to 3 years after explosion. The supernova is still clearly detected on top of a faint galaxy!

The first paper focuses on new Hubble Space Telescope observations of my old friend, SN 2015bn. The HST data show that this event was much brighter than expect at 700-1100 days after peak luminosity, indicating a very slowly-evolving power source. After testing out a lot of models, the most consistent explanation seems to be a central engine such as a millisecond magnetar, the same scenario that best explained earlier data!

The second paper focuses on long-term spectroscopy of a sample of 12 superluminous supernovae at about 100 to 500 days after explosion. We applied statistical techniques and machine learning algorithms to calculate their average observable properties and diversity, and investigated their physical properties using the velocities and ratios of important spectral lines. This allowed us to construct a picture of the explosion from the inside out, which can be used in future as the input for more detailed simulations.

schematic
Our physical picture of the material ejected by superluminous supernovae, showing the layers and clumps with different chemical compositions and velocities

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