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

Weiyu Wu, Ji-an Jiang, Zelin Xu, Dezheng Meng, Keiichi Maeda, Hanindyo Kuncarayakti, Lluís Galbany, Saurabh W. Jha, Željko Ivezić, Peter Yoachim, Zhengyan Liu, Junhan Zhao, Tinggui Wang, Xu Kong, Andrew J. Connolly, Ziqing Jia, Lei Hu, Lulu Fan, Ning Jiang, Feng Li, Ming Liang, Jinlong Tang, Zhen Wan, Hairen Wang, Jian Wang, Yongquan Xue, Hongfei Zhang, Wen Zhao, Xianzhong Zheng, Qingfeng Zhu

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.

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

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.
Paper Structure (16 sections, 2 equations, 14 figures, 3 tables)

This paper contains 16 sections, 2 equations, 14 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Observations and Sample Overview
  3. SN Ia Classification
  4. WFST-PS SNe Ia
  5. Light Curve
  6. WFST-PS EExSNe Ia
  7. Host Galaxies
  8. Results
  9. The Luminosity-Decline Relation
  10. Rise Time
  11. Color
  12. Discussion
  13. Ejecta-companion Interaction
  14. Surface $^{56}$Ni Decay
  15. Double-detonation Scenario
  16. ...and 1 more sections

Figures (14)

  • Figure 1: The redshift distribution of WFST-PS early-phase SNe Ia. Photometric redshifts of two host galaxies are used due to the missing of spectroscopic redshifts of both SNe and hosts.
  • Figure 2: Spectra and SNID classification results for four early-phase SNe Ia. From top to bottom: WFST-PS240407h, WFST-PS240410d, WFST-PS240504x, and WFST-PS240513c. The colored lines and their corresponding labels represent the matched template spectra, while the gray lines show the observed spectra of each early-phase SNe Ia. The probability matches with $rlap \geq 5$ are presented to ensure reliable classification.
  • Figure 3: Light curves of 16 WFST-PS early-phase SNe Ia in the $u$, $g$, and $r$ bands with their SALT2 best-fit models. The $u$, $g$, and $r$ bands are represented by purple, blue, and green colors, respectively.
  • Figure 4: Top: Early light-curves of WFST-PS240315d, WFST-PS240407h, and WFST-PS240513c. The single power-law fits (dashed lines) and power-law + Gaussian fits (solid lines) are shown for each object. $g$-band and $r$-band data with their respective fits are plotted in blue and green. For comparison, the EExSN Ia SN 2017cbv is plotted in red ($U$-band: solid diamonds; $g$-band: open diamonds), while the non-EExSN Ia SN 2011fe is shown in black ($U$-band: solid squares; $g$-band: open squares). Middle: residuals relative to a single power-law fit. Bottom panels: the excess as flux subtracted by the power-law component in the power-law + Gaussian fit, and the corresponding residuals.
  • Figure 5: Color images of WFST-PS early-phase SN Ia hosts. The position of each supernova within its host galaxy is marked by a red pentagram. The images were obtained from the DESI DR1 data releases 2025arXiv250314745D.
  • ...and 9 more figures