Pre-discovery detection of the M31 nova AT 2021ypn
ATel #14922; K. Sarneczky, A. Horti-David, J. Vinko, Cs. Kalup (Konkoly Observatory)
on 17 Sep 2021; 20:25 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)
We report pre-discovery detection of the M31 nova AT 2021ypn (PSP21H) discovered by the Xingming Observatory Sky Survey (XOSS) on 2021-09-11.602 UT and classified as a nova by Valcheva et al. (ATel #14913) and Vinokurov et al. (ATel #14919).
AT 2021ypn was first detected on the unfiltered, co-added frames (exposure time 15x60 sec) taken with the 10560x10560 STA 1600LN CCD on the 0.6/0.9m Schmidt telescope at Piszkesteto Station of Konkoly Observatory, Hungary, at 2021-09-10.968 UT, ~15.2 hours before discovery. Image subtraction using a template frame taken on 2020-10-22 has been applied before detection. The last non-detection with the same setup occurred at 2021-09-10.09 UT, ~21.07 hours before our first detection.
The nova appeared 0.6 (unfiltered) mag fainter at 2021-09-10.97 UT than 1 day later, at 2021-09-11.9 UT, close to the discovery date. Using the R-band photometry of Valcheva et al. (ATel #14913) we estimate the pre-discovery brightness of AT 2021ypn as R ~ 17.0 +/- 0.1 mag.
