A Type Ia Supernova Candidate at z about4.3: A Transient Interloper in the Search for z about14 Galaxies

The James Webb Space Telescope (JWST) is opening a new window into the distant Universe by discovering galaxies and transients in the early Universe. We investigate a high-redshift transient candidate, beacon 1420-5253 4770. This object was initially identified as a high-redshift galaxy candidate at z about14. However, the source was not detected in epochs before and after the detection epoch, suggesting that the object is a transient source rather than a persistent galaxy. We classify the source by comparing the colors, magnitudes, light curves, and spectral energy distribution with various spectral templates of transients. Our analysis shows that the observed properties are consistent with a Type Ia supernova at z about4.3. Strong absorption by Fe-group elements seen in Type Ia supernova spectra can mimic the Lyman break used to detect high-redshift galaxies. At z about 4.3, corresponding to a cosmic age of only about 1.5 Gyr, our detection provides a direct probe of the delay time between star formation and supernova explosion. Our estimate of the event rate implies a minimum delay time shorter than 1 Gyr. We also discuss the implications of transient contamination for searches of galaxies in the early Universe.