AstroNote 2023-338

We observed the field of the AT 2023zaw (ZTF23absbqun; Sollerman et al., 2023TNSTR3158....1S; Karambelkar et al., AstroNote 2023-335) as part of the Kinder project (Chen et al., AstroNote 2021-92). We used the 40cm-SLT at Lulin Observatory, Taiwan to obtain images in u, g, r, i, and z filters for 4 epochs with a daily candence, exposure time 300 seconds for single frame in griz and 300 second times two frames for u band. The first image was taken at 17:00 UT on 08 of December 2023 (MJD = 60286.716), 11.62 hours after the ZTF discovery and our last epoch was taken on 11 Decmeber 2023 (MJD = 60289.695).

We used the Kinder pipeline (Yang & Sollerman 2023) to measure the PSF photometry of AT 2023zaw without template subtraction, with a caution that there maybe some host background comtamination for our photometry measurements. The preliminary magnitudes are calibrated against PanSTARRS1 field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.22 mag in the direction of the counterpart (Schlafly & Finkbeiner 2011). 

We observe a clear and significant fading in g-band and slowly fading in redder bands espacially in z band over the 4 nights from 2023-12-08 to 2023-12-11:
delta-g = 0.8 +/- 0.2, and
delta-z = 0.2 +/- 0.1. 

The g-band magnitude at MJD = 60289.684 is g = 19.8 +/- 0.2 mag. This observation supports the rapid fading of AT 2023zaw, confirming the fast fading and red nature reported by Karambelkar et al. (AstroNote 2023-335). We also note that the decline rate is strongly colour dependent, which may indicate rapid cooling or line opacity in the blue.