We report observations of a Type Ia supernova (SN Ia) 2021hem that was discovered within 48 hours of last nondetection and is located in an apparently hostless environment. With a peak absolute B-band magnitude of M_ ***The English in this work is already good and did not require full language editing. I have corrected the Abstract, Introduction, Conclusion and the first sentences of the figure captions in detail and added notes that are to be applied throughout the paper. Please review these notes below and apply the corrections to the whole paper. For more details, see: https: //www. aanda. org/ images/stories/author/EnglishGuide-2021. pdf Convention - I have edited to US English*** B, = -19. 96 ± 0. 29, mag, lies at the luminous end of the ***please introduce all your abbreviations and acronyms at first occurrence in the Abstract and again in the main text (because the Abstract is considered a stand-alone item) and then use them throughout without reintroduction, including all figure captions and tables. Please check this throughout and amend as required*** SNe Ia distribution. Its near-infrared and i-band light curves lack the secondary maximum, which is otherwise ubiquitous to normal and 1991T-like SNe Ia. Instead, these properties cause (B) = 1. 02 ± 0. 02 mag; s_ to closely resemble 2003fg-like events. The slowly evolving light curves (characterized by Δ m_ 15 BV = 0. 94 ± 0. 05) and the earliest spectrum showing łd6580 and łd7235 absorption lines further support this classification. Other spectroscopic features, including = -16. 43^ C ii line diagnostics, resemble those of normal SNe Ia. A fit of a fireball model to the early-time light curves yields a time of first light of t_ ***your quotes here and throughout are redundant. Please remove them throughout*** ̊m first +0. 45 _ -0. 38, days relative to B-band maximum. The first photometric detection occurs 1. 51^ +0. 45 _ -0. 38, days before the onset of fireball-like flux rise. This early emission, together with the intrinsic (g - r) ₀ color, is inconsistent with circumstellar or companion interaction. Instead, shallow ∋ckel mixing or an asymmetric ∋ckel distribution offers a plausible explanation for the delayed onset of the fireball flux rise, while a double-detonation scenario with a thin helium shell remains a less likely alternative. Notably, represents the fifth known 2003fg-like SN that has early-time activity or excess flux emission. The estimated mass of radioactive ∋ckel synthesized in is 1. 00 ± 0. 09, = 24. 4, mag and a surface-brightness limit of μ_ Deep GTC imaging obtained 2. 5, years after the explosion, with an estimated limiting magnitude of m_ lim, r lim, r = 26. 3,. A faint diffuse feature approx6̨pc from the SN site has also been detected in the GTC image, and its surface brightness is within the limits of UDGs. It is unclear whether it is a galaxy and is associated with revealed no coincident host. Most faint dwarf and ultradiffuse galaxies (UDGs) are therefore ruled out. Alternatively, if the nearest plausible AGN host galaxy located at a projected distance of 104, ̨pc is assumed, the progenitor would need to be a hypervelocity star ejected at approx2200, ̨ms from the host by AGN interaction ***you use the single and double tilde to signify "approximately". Please decide which way you wish to write this and then stick to it throughout for consistency (either is fine, but just one in a given paper*** however. Based on its large normalized directional light distance (approx3-4) from the SN and its unusual elongation, the probability that this is the candidate host galaxy of is low. These results identify as one of the strongest candidates for a hostless SN Ia and underscore the diversity of luminous slowly evolving 2003fg-like explosions and the wide range of environments in which they may occur.
Bose et al. (Wed,) studied this question.