AstroNote 2025-173

We observed the field of SN 2025mvn (ATLAS25fwv; Smith et al., AstroNote 2025-171), classified as a Type II SN (Andrews et al., TNS Classification Report No. 21220), as part of the Kinder collaboration (Chen, Yang et al. 2025, ApJ, 983, 86). Observations were carried out using the 1-meter telescopes in Altay, Xinjiang (Longitude: 88°43′35″, Latitude: +47°35′24″, Altitude: 1025 m) in the g, r, i, and z filters.

Our imaging began at 16:41 UT on 2025 June 3 (MJD = 60829.69), 8.88 hours after the ATLAS discovery. Images were obtained under seeing conditions (FWHM ~ 1.6″), with an average airmass of 1.1. 

We processed the data using the dedicated Kinder pipeline (Yang et al. 2021, A&A, 646, A22), which includes image calibration, subtraction using SDSS templates, and PSF photometry at the source location. The measured AB magnitudes are as follows:
g = 18.34 ± 0.10 mag,
r = 17.49 ± 0.17 mag,
i = 17.24 ± 0.13 mag, and
z = 17.15 ± 0.15 mag.

These magnitudes were calibrated against SDSS field stars and are not corrected for Galactic extinction, which corresponds to a foreground reddening of A_g = 0.04 mag in the direction of the source (Schlafly & Finkbeiner 2011). The observed colour is notably red, likely due to internal extinction in the host galaxy. 

Comparing with the ATLAS o-band discovery magnitude of 18.22 ± 0.14 on MJD 60829.32, our r-band measurement shows a brightening of approximately 0.7 mag within 9 hours, consistent with the expected rapid rise of a young Type II supernova.