WFST Supernovae in the First Year: I. Statistical Study of 16 Early-phase Type Ia Supernovae from the Pilot Survey

TL;DR

This study reports the discovery and analysis of 16 early-phase Type Ia supernovae from the WFST-PS survey, highlighting diverse early behaviors, the significance of early NUV observations, and the need for improved theoretical models.

Contribution

First comprehensive early-phase SNe Ia sample from WFST-PS, revealing diverse behaviors and emphasizing the importance of early NUV data for understanding explosion mechanisms.

Findings

16 early-phase SNe Ia discovered with faint magnitudes

Diverse early color indices indicating varied photometric behaviors

Early NUV observations are crucial for constraining explosion models

Abstract

In this paper we present 16 early-phase type Ia supernovae (SNe Ia) discovered during the pilot survey of the 2.5-meter Wide Field Survey Telescope (WFST-PS) from March 4 to July 10, 2024, including three SNe Ia with early-excess emission features (EExSNe Ia). The discovery magnitude of the 16 WFST-PS early-phase SNe is at least 3 mag fainter than their peak brightness. A large scatter of color indices is found in approximately the first 10 days of supernova explosions, indicating diverse photometric behaviors in the early phase. Three EExSNe Ia show relatively brighter peak luminosities and longer rise time compared to those of non-EExSNe Ia. The results indicate that current theoretical models require further refinement to fully capture the early photometric evolution of SNe Ia. Based on the initial high-cadence ugr-band data from the WFST-PS survey, we emphasize that early near-ultraviolet (NUV) observations are indispensable for placing tight constraints on the explosion mechanisms and progenitor systems of SNe Ia.