AstroNote 2021-132

We report the identification of a fast-evolving transient by the Zwicky Transient Facility. 

AT2021izg (ATLAS21lwz, ZTF21aatsawe) was reported to TNS by the ATLAS survey based on a c-band detection at 19.94 mag on April 10. The first ZTF detections were at r=19.80 +/- 0.17 and g=19.34+/-0.10 on 2021 April 9. The last upper limit was at g > 20.73 on 2021 April 8. On April 11, the light curve peaked at g=19.30 +/- 0.11 and r=19.18 +/- 0.22. AT2021izg stayed at  g ~ r ~ 19.4 on April 12 and 13. Since April 13, it has been fading gradually (~0.14 mag/day). By April 20, the source had faded to g = 20.36 +/- 0.19 and r = 20.61 +/- 0.25. The post-peak color is consistent with g-r ~ -0.2. The Galactic extinction towards AT2021izg is E(g-r) = 0.04. 

The total duration above half-max is 7 days in r-band and 10 days in g-band. AT2021izg therefore fulfills the criteria that have been used to identify fast-evolving transients (Drout et al. 2014, ApJ, 794, 23), and is significantly shorter than typical supernovae (Perley et al. 2020, ApJ, 904, 35).

There was no historical detection in PTF, ATLAS, and ZTF. Within 10 arcsec from the position of AT2021izg, there is no optical source in the SDSS, PS1, and Legacy Survey (LS) catalogs. The LS depth in this field is g>24.4, r>23.9, and i>23.2. We encourage spectroscopic follow-up and classification of this transient.