AstroNote 2023-268

We report the discovery of a rapidly rising and blue transient AT2023ufx (ATLAS23tsa). AT2023ufx was discovered by ATLAS on MJD 60223.58 (2023-10-06.58) at an o-band magnitude of 17.55 +/- 0.09. 4 days later on MJD 60227.58, the transient had risen to an o-band magnitude of 15.91 +/- 0.03. Subsequently, the transient was detected by ZTF (ZTF23abjjqxf) on MJD 60229.44 in the g and r bands with a blue colour, g-r ~ -0.13 (after accounting for Galactic extinction). The transient is likely associated with a faint, blue galaxy SDSS J082451.42+211743.4 with a photometric redshift of z ~ 0.04. At this redshift, the absolute magnitude from the latest ZTF detection is Mg ~ -20.7 +/- 0.2. There was no detection by ZTF on MJD 60222.49 to a limiting magnitude of r > 19.34, ~1 day prior to the ATLAS discovery. This suggest a 4-5 day rise to its current luminosity. 

The combined ATLAS+ZTF photometry of AT2023ufx suggests a rapid rise, blue color and high luminosity. Together, this indicates that AT2023ufx is a candidate luminous fast blue optical transient or LFBOT like AT2018cow. Spectroscopic classification and multi-wavelength observations are encouraged.

The Asteroid Terrestrial-impact Last Alert System [ATLAS] project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile.