| dc.description.abstract | Type Ia Supernovae (SNe Ia) have played an important role in modern cosmology as distance indicators and have led to the discovery of the accelerated expansion of the universe. Such usage of SNe Ia hinges upon the precision photometry of SNe Ia and that their peak luminosities can be corrected onto a standard magnitude using empirical relationships like luminosity-decline relation. However, intrinsic scatter exists beyond errors and uncertainties introduced by photometry reductions and empirical corrections. The full details of the underlying explosion mechanism also remain unclear despite the commonly agreed thermonuclear explosion picture.
To better understand the systematics in using SNe Ia in cosmology, we developed our own photometry reduction pipeline that uses a novel image subtraction software (SFFT) developed by our collaborator for a cleaner subtraction of the underlying galaxy, and does point-spread-function (PSF) photometry simultaneously on multiple images while maintaining a common coordinates for field stars to improve the photometric precision.
Our photometry pipeline is applied to 16 luminous 91T/99aa-like SNe Ia observed by Las Cumbres Observatory. Additionally, we gathered 21 91T/99aa-like well observed SNe Ia from the literature to study the standardizability of 91T/99aa-like objects. We found that 91T/99aa-like SNe Ia are excellent distance indicators but have a brighter Hubble residual than normal SNe Ia after fully corrected. Moreover, we found that the pseudo-equivalent width (pEW) of Si II λλ 6355 near maximum light is correlated with Hubble residuals when pEW(Si II λλ 6355) is less than 55.6 Å. This new systematic needs to be taken care of to safely use SNe Ia in cosmology especially in the upcoming era of LSST, as luminous 91T/99aa-like SNe will be inevitably biased in flux-limited surveys and 91T/99aa-like SNe are hard to distinguish from normal SNe Ia without spectroscopic observations before maximum.
We also applied our photometry pipeline to the data taken by our DECam survey of Intermediate Redshift Transients (DESIRT). We found 923 transient candidates with 235 being off-nuclear ones. We discovered many SNe Ia at very early phase with decent light curves reduced. Besides normal SNe Ia, we also discovered some 91T/99aa-like SNe Ia, and even one extremely rare 00cx-like SN Ia. With this dataset, we will be able to study SNe Ia at infant phase, recalculate the rate of 91T/99aa-like SNe, and improve cosmology with SNe Ia as standard candles. | |
