Supernovae and the transient sky with the Legacy Survey of Space and Time and spectroscopy from ESO facilities

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will start in January 2025 and is expected to completely revolutionise transient astronomy and, in particular, cosmological measurements using Type Ia supernovae.

Rubin and LSST involve a wide network of international scientists, and our team is leading the preparation for the beginning of the survey and will be heavily involved in the analysis of the first transient data. We work on a wide range of projects (both observations oriented and simulations oriented) that will have a high impact on LSST science. These projects revolve around the development and testing of transient discovery and classification pipelines, design and optimisation of LSST spectroscopic follow-up programs, and the design of new strategies to use and compile cosmological samples using LSST supernova data.

We are also leading various analyses of recently concluded supernova surveys like the Dark Energy Survey supernova sample (the largest and deepest supernova survey from a single telescope in the pre-LSST era) and current/upcoming SN surveys with the space telescopes Euclid (an ESA led facility, now working) and Nancy Grace Roman (a future NASA mission). These surveys will provide tremendous datasets to tackle some of the most pressing questions in supernova cosmology and astrophysics.

The DPhil project can focus on either the astrophysics of the explosions or the application to cosmology. On the astrophysics side, we aim to answer the question of how do white dwarfs explode to give type Ia supernovae and how many possible stellar evolutionary channels lead to this end point. How they are affected by dust extinction and their host galaxy properties critically affect their use as cosmological probes.

Over the last number of years a number of explosive transients have been discovered with uncertain physical nature. These include fast x-ray transients, luminous fast blue optical transients and infrared transients associated with long gamma ray bursts. They may be tidal disruption events from intermediate mass black holes, black hole forming supernovae, and kilonovae from merging neutron stars.

The Rubin Observatory will begin operations in late 2025, providing the deepest time domain survey of the sky ever undertaken. Combing the optical discoveries with high energy and radio surveys has the potential to unveil the nature of these source and may reveal new populations. We use machine learning methods to discover and classify these transients in ongoing sky surveys.

The Rubin Observatory will provide the largest sample of type Ia supernovae for cosmology and understanding the physics of the explosions. The unprecedented precision of the lightcurves and large statistical samples will mean that uncertainties in the cosmological parameters becomes limited by the systematics within the supernova analysis.

By combining the nightly data flow from LSST with high energy (gamma to x-ray) emission and fast spectroscopic classification from the new spectrometer at the European Southern Observatory (SOXS), and the extensive 4MOST multi-fibre spectrometer (within the TiDES survey) we will discover hundreds of thousands of transients, take spectra of tens of thousands, along with host galaxy data.

This will allow us to understand the physics of stellar explosions, the demographics of the population, and ultimately the constraints on the cosmological analysis.