Observational properties of a general relativistic instability supernova from a primordial supermassive star

Abstract

ABSTRACT We present the expected observational properties of a general relativistic instability supernova (GRSN) from the 55 500 M⊙ primordial (Population III) star. Supermassive stars exceeding $10^4\, \mathrm{M}_\odot$ may exist in the early Universe. They are generally considered to collapse through the general relativistic instability to be seed black holes to form supermassive ($\sim 10^9\, \mathrm{M}_\odot$) black holes observed as high-redshift quasars. Some of them, however, may explode as GRSNe if the explosive helium burning unbinds the supermassive stars following the collapse triggered by the general relativistic instability. We perform the radiation hydrodynamics simulation of the GRSN starting shortly before the shock breakout. We find that the GRSN is characterized by a long-lasting (550 d) luminous ($1.5\times 10^{44}\, \mathrm{erg\, s^{-1}}$) plateau phase with the photospheric temperature of around 5000 K in the rest frame. The plateau phase lasts for decades when it appears at high redshifts and it will likely be observed as a persistent source in the future deep near-infrared imaging surveys. Especially, the near-infrared images reaching 29 AB magnitude that can be obtained by Galaxy and Reionization EXplorer (G-REX) and James Webb Space Telescope (JWST) allow us to identify GRSNe up to z ≃ 15. Deeper images enable us to discover GRSNe at even higher redshifts. Having extremely red colour, they can be distinguished from other persistent sources such as high-redshift galaxies by using colour information. We conclude that the deep near-infrared images are able to constrain the existence of GRSNe from the primordial supermassive stars in the Universe even without the time domain information.