Alice Townsend

Hi! I'm Alice Townsend, a PhD student at the Humboldt University of Berlin in Germany. I started in November 2021, and I work with the Zwicky Transient Facility (ZTF) to discover and analyse explosive transients known as supernovae. My main research areas are strong gravitationally lensed supernovae and the photometric classification of supernovae. Prior to this, I obtained my master's in physics (MPhys) from the University of Manchester (Sept 2017 - Jul 2021), with a thesis on the study of transitional millisecond pulsars.

Strongly lensed supernovae

Strong gravitational lensing is a consequence of general relativity, where light from a bright background source is deflected and magnified by an intervening massive object. Strong lensed supernovae, in particlar Type Ia supernove, allow us to calculate cosmological parameters, distributions of dark matter, as well as the astrophysics of the supernovae and the intervening lensing galaxies themselves. My work involves searching for lensed supernovae in archival and live data from ground-based telescopes such as ZTF.

Photometric classification of supernoave with ML

We are in an era of astronomy where we have an unprecedented amount of photometric data (i.e. light curves) of transients, but not enough spectroscopic resources to follow up and classify every object. In this case, photometric classification with machine learning is neccessary to type each supernova we detect. This is important for improving statistics in Type Ia cosmology, as well as for rate studies of each class. My research is applying photometric classification methods to live and archival ZTF extragalactic transients.

SN Ia cosmology

Type Ia supernovae are bright, standardisable candles that are used to form a distance ladder in cosmological measurements. An exciting application of my photometric classification work is that we will soon be able to photometrically classify the entire ZTF extragalactic transient sample. This should provide us with more than 50,000 Type Ia supernovae, which will be an excellent dataset to use in cosmological analyses. This will allow us to measure, for example, the Hubble constant, the fraction of matter in the Universe (Ω_M), and the growth of fluctuations in the early universe (σ₈).

Candidate strongly lensed type Ia supernovae in the Zwicky Transient Facility archive

We conducted a systematic search through three and a half years of the ZTF archive and found two promising lensed Type Ia supernova candidates. This required an efficient analysis pipeline that removed possible contaminants (such as SLSNe), whilst retaining objects that displayed the characteristics of lensed supernovae.