Thursday, March 14, 2013

Dual-Shock Quark Nova

A super-luminous supernova (SLSN) is a class of supernova whose peak luminosity is several times larger than a typical supernova. Mechanisms that can give rise to a SLSN include the explosion of a very massive star in a pair-instability supernova, the interaction of supernova ejecta with circumstellar matter or a dual-shock quark nova (dsQN) event. SN 2006oz is currently the only SLSN known to exhibit a double-humped lightcurve that is consistant with a dsQN model. The lightcurve of SN 2006oz can be explained by a quark nova occurring 6.5 days after a core-collapse supernova explosion. A dsQN event like SN 2006oz is very rare since it is estimated to occur at a rate of 1 in every 10,000 core-collapse supernovae.

In a dsQN model, a massive star explodes in normal core-collapse supernova and leaves behind a rapidly-spinning, high-mass neutron star. As the neutron star spins down, its central density gradually increases. This eventually leads to a detonative phase transition known as a quark nova, where the neutron star violently converts into a quark star. During this process, the neutron star’s outer layer is ejected at ultra-relativistic velocities. An enormous amount of kinetic energy is carried away since the quark nova ejecta consists of ~100 Earth masses of material travelling close to the speed of light.

Although the quark nova occurs several days after the core-collapse supernova, ejecta from the quark nova travel many times faster than the supernova ejecta. The quark nova ejecta rapidly catch up and collide with ejecta from the preceding supernova. This re-shocks the supernova ejecta and leads to a rise in luminosity over an extended period of time. As a result, a SLSN consisting of a normal core-collapse supernova followed by a quark nova is characterised by a double-humped lightcurve. The fainter first hump corresponds to the core-collapse supernova while the brighter second hump corresponds to the re-shocked supernova ejecta.

A double-humped lightcurve indicative of a dsQN is only produced when the quark nova happens ~10 days after the core-collapse supernova. If the time interval between the supernova and quark nova is too long, the supernova ejecta would have dissipated so much that the quark nova basically occurs in isolation. In contrast, if the time interval is too short, the two lightcurves would overlap and prevent a distinct double-hump.

1. D. Leahy and R. Ouyed (2013), “Double-humped Super-luminous Supernovae”, arXiv:1303.2047 [astro-ph.HE]
2. Giorgos Leloudas et al. (2012), “SN 2006oz: rise of a super-luminous supernova observed by the SDSS-II SN Survey”, arXiv:1201.5393 [astro-ph.SR]