Normal or transitional? The evolution and properties of two type Ia supernovae in the Virgo cluster
Abstract
Type Ia supernovae (SNe Ia) are among the most precise cosmological distance indicators used to study the expansion history of the Universe. The vast increase of SN Ia data due to large-scale astrophysical surveys has led to the discovery of a wide variety of SN Ia sub-classes, such as transitional and fast-declining SNe Ia. However, their distinct photometric and spectroscopic properties differentiate them from the population of normal SNe Ia such that their use as cosmological tools remains challenged. Here, we present a high-cadenced photometric and spectroscopic dataset of two SNe Ia, SNe 2020ue and 2020nlb, which were discovered in the nearby Virgo cluster of galaxies. Our study shows that SN 2020nlb is a normal SN Ia whose unusually red color is intrinsic, arising from a lower photospheric temperature rather than interstellar reddening, providing clear evidence that color diversity among normal SNe Ia can have a physical origin. In contrast, SN 2020ue has photometric properties, such as color evolution and light-curve decay rate, similar to those of transitional SNe, spectroscopically it is more aligned with normal SNe Ia. This is evident from spectroscopic indicators such as the pseudo-equivalent width of \ion{Si}{II} lines. Thus, such SNe Ia that are photometrically at the edge of the standard normal SNe Ia range may be missed in cosmological SNe Ia samples. Our results highlight that spectroscopic analysis of SNe Ia around peak brightness is crucial for identifying intrinsic color variations and constructing a more complete and physically homogeneous SN Ia sample for precision cosmology.
Keywords
Cite
@article{arxiv.2512.00555,
title = {Normal or transitional? The evolution and properties of two type Ia supernovae in the Virgo cluster},
author = {L. Izzo and C. Gall and N. Khetan and N. Earl and J. Hjorth and W. B. Hoogendam and Y. Q. Ni and A. Sedgewick and S. M. Ward and Y. Zenati and K. Auchettl and S. Bhattacharjee and S. Benetti and M. Branchesi and E. Cappellaro and A. Catapano and K. C. Chambers and D. A. Coulter and K. W. Davis and M. Della Valle and S. Dhawan and T. de Boer and G. Dimitriadis and R. J. Foley and M. Fulton and H. Gao and W. J. Hon and M. E. Huber and D. O. Jones and C. D. Kilpatrick and C. C. Lin and T. B. Lowe and E. A. Magnier and K. S. Mandel and R. Margutti and G. Narayan and P. Ochner and Y. C. Pan and A. Reguitti and C. Rojas-Bravo and M. Siebert and S. J. Smartt and K. W. Smith and S. Srivastav and J. J. Swift and K. Taggart and G. Terreran and S. Thorp and L. Tomasella and R. J. Wainscoat},
journal= {arXiv preprint arXiv:2512.00555},
year = {2026}
}
Comments
24 pages, 21 figures, 7 tables. Accepted for publication in A&A