Nearby Supernova Science in the Era of High Cadence, Deep Time Domain Surveys

The paper discusses science opportunities for nearby supernovae (SNe) with Rubin Observatory's Legacy Survey of Space and Time (LSST), focusing on the youngest phases of SN evolution and the value of contemporaneous high-cadence shadowing surveys. LSST's Wide Fast Deep survey will discover enormous numbers of SNe, but its ~3 day cadence will miss signatures evolving on hours-to-days timescales, so other programs must augment the cadence.

The authors present simple depth and cadence metrics for early SN signatures and use empirical nearby SN discovery rates to estimate the resulting science opportunities.

They estimate LSST will detect or set limits on precursor emission from hundreds of core-collapse SNe, including ≳50-100 Type IIn and normal Type II SNe annually, plus ≳5 Type Ibn. Within ~200 Mpc, roughly 250 Type Ia SNe are classified each year, offering the potential to identify hundreds of early light-curve excesses and to robustly measure the incidence of extreme high-velocity features (>25,000 km/s). A shadowing survey reaching ~22.5 mag could search for early light-curve features like the excess seen in SN2023ixf across dozens of nearby core-collapse SNe per year. Rapid spectroscopy of ≳150 Type II SNe per year within ~160 Mpc could constrain the incidence of short-lived flash features to ≲10% within a few years and tie it to the precursor-emission rate in normal Type II SNe.

The paper also discusses challenges from early classification ambiguity and faint nonterminal transients. It requests that the 80 hour embargo on LSST images be waived for nearby galaxy fields, and advocates for a Nearby Galaxy Transient Broker that integrates transient streams, archival data, forced photometry, and follow-up triggering in a single platform.