AstroNote 2022-39

We observed the field of the AT 2022cmc/ZTF22aaajecp (AstroNote #2022-38, Andreoni et al.) as part of the Kinder (kilonova finder) survey (AstroNote #2021-92, Chen et al.). We used the 0.4m-SLT at Lulin Observatory, Taiwan, to obtain images in g, r, and i filters. 

Observations started at 19:15 UT on 14 of February 2022 (MJD = 59624.803), 3.36 days after the first detection with ZTF (2022-02-11). The images were taken under a various seeing conditions 2".5 and at an average airmass of 1.0. 

We used the AUTOmated Photometry Of Transients (AutoPhOT) pipeline (Brennan & Fraser, 2022) to measure the PSF photometry of AT 2022cmc without template subtraction. The  following are preliminary magnitudes (all in the AB system):

g = 20.303 +/- 0.56 mag  (SNR~2.5),
r > 20.04 mag (SNR~1.6), and
i = 19.83 +/- 0.38 mag (SNR~3.1) .

Given magnitudes are calibrated against SDSS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V) = 0.01 mag in the direction of the AT2022cmc (Schlafly & Finkbeiner 2011). 

Comparing with the ZTF observed peak on 2022-02-12 via the Lasair broker (Smith, Williams, Young et al. 2019), 2022cmc has declined roughly 0.4 and 0.3 mag per day in i and g band correspondingly, and more than 0.4 mag per day in r.