‘Superluminous’ supernova grows extremely slowly
Researchers have observed the longest-ever rise time for in a superluminous supernova to date, according to a new report.
A superluminous supernova, or hypernova, releases substantially more energy than the standard supernova, and the one recently reported on, dubbed PS1-14bj, captured astronomers’ attention when they saw that its rise in brightness to maximum light occurred much more slowly than normal.
The phenomenon was originally detected by the Pan-STARRS telescope (PS1) on Mount Haleakala in Hawaii, and through follow-up observations, the team was able to obtain spectra and more optical data of PS1-14bj. As it turns out, the supernova advanced very slowly, with a rise time to optimum that took greater than 120 days. The hypernova also faded away very slowly, over the course of around 250 days.
Standard supernovae take just a few weeks to rise to peak brightness, and hypernovae take around 30 to 50 days.
The study team said this lazy development is what might be expected for a unique kind of explosion system known as a pair-instability supernova, and PS1-14bj matches some of the theoretical expectations of how this kind of explosion might appear.
However, it also had some attributes that are very difficult to explain in a pair-instability situation. What baffles the researchers is a strange color progression, with the color temperature increasing prior to maximum, and remaining constant through the peak and decrease. The team said the hypernova stayed blue, suggesting high temperatures, as it fades away, as opposed to cooling.
“This means that there is some energy source heating the supernova ejecta at very late times, and it’s unclear what that energy source is,” study author Ragnhild Lunnan, of the California Institute of Technology, told Phys.org. One possibility is that there is material around the star, a shell of gas that got ejected from the star before it exploded, and as the supernova explosion runs into this the gas is heated by the collision.”
Another potential explanation is that the supernova might be powered by a magnetar, a quickly spinning neutron star with a strong magnetic field . The study team said the magnetar could also be heating material released by the supernova for very long times.
“Every time we discover something we haven’t seen before, it adds to our understanding,” Lunnan said. “For example, PS1-14bj shows us that there exist superluminous supernovae that have the kind of broad, slow light curves that are predicted by pair-instability supernova models. Of course, discovering new things also tends to add to the list of things we don’t yet understand, but that is part of the fun of doing science.”
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Image credit: Lunnan et al., 2016.
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