My research revolves around understanding exotic transients – events whose properties differ from those of ‘normal’ supernovae, which often require extreme physical scenarios to explain. I use observational data to study the most extreme transients in the Universe, so that I can unveil their physical origins. Some of the types of transients I am interested in are:
Fast Rising Tidal Disruption Events
Tidal Disruption Events (TDEs) are the luminous flares produced when a star strays close to a black hole (BH), and is shredded by the strong gravitational field then partially accreted onto the BH. Studying these events is important, as they provide insights into the physics behind accretion processes in BHs.
Using data from the Young Supernova Experiment, we identified AT2020neh, a TDE, which reached peak luminosity in just 13 days. The exceptionally fast rise of AT2020neh is due to the mass of the BH which disrupted the star, which is an Intermediate Mass Black Hole (IMBH). IMBHs are an elusive population of BHs, which are very difficult to identify. If we can find more fast-rising TDEs like AT2020neh, we may be able to use them to identify populations of IMBHs. As IMBHs are believed to be the initial seeds from which more massive black holes grow, this may help us to understand the growth and evolution of the massive BHs we see at the hearts of galaxies.
Superluminous Supernovae
Superluminous Supernovae (SLSNe) are an exceptionally bright subclass of supernovae. At peak, they’re typically 10 times brighter type Ia supernovae, and more than 100 times brighter than “normal” core collapse ones. They’re also very long lived events, remaining bright at optical wavelengths for ~100’s of days. Such events have the potential to be seen out to very large cosmic distances, which makes them an appealing candidate class of events to use as distance measures in cosmology.
However, before we can do this, we have to really understand how SLSNe are produced. This is a topic is still currently under debate. Their longevity and high luminosities of SLSNe makes the difficult to describe with normal core collapse physics, requiring large amounts of 56Ni to be produced during the explosion in order to produce the main peak of the lightcurve, whilst their declines rates are much swifter than would be expected if driven by radioactive decay.
My research involves the study of these events, particularly the sample found within the Dark Energy Survey. Through study of their lightcurves (see below for an example ), we may begin to understand the physics behind these explosions. Within SLSNe, we see lots of diversity within their lightcurve behaviours – a wide range of evolutionary timescales and peak brightnesses. Some events even show re-brightening at late times.
Bumpy SLSNe
One feature of SLSNe I’m particularly interested in are pre-peak bumps – these are small peaks which occur a few days prior to the start of the main supernova. It’s thought that these occur due to a process called shock breakout – a burst of high energy radiation which is visible when the shock from the supernova explosion first “breaks out” of the stellar surface. In SLSNe, we think this shock breakout can interact with a dense shell of surrounding material, which we see as a bump!
Some of my work with the DES SLSN sample has involved studying the properties of these bumps, (which are as diverse as the SLSN sample!), and in some cases, we can completely rule out their presence!
The arms help.
Host Galaxies
A complementary route to understanding the progenitors of different kinds of transients is to look at the environments in which they occur. From the properties of the environment in which a star explodes, we can make general assumptions about the underlying population of stars within the galaxy, and therefore the most likely progenitor type to have produced the transient.
Dr Charlotte Angus 