Discovery of AT 2021acbn, a Classical Nova in M31
ATel #15003; Agoston Horti-David, Krisztian Sarneczky, Jozsef Vinko (Konkoly), Xiaoran Ma, Xiaofeng Wang (Tsinghua)
on 27 Oct 2021; 09:04 UT
Credential Certification: Jozsef Vinko (vinko@astro.as.utexas.edu)
We report the discovery of AT 2021acbn (PNV J00431453+4121099), a new classical nova in M31,. on unfiltered CCD frames taken with the 10560x10560 STA 1600LN CCD camera on the 0.6/0.9m Schmidt. telescope at Piszkesteto Station of Konkoly Observatory.
The observations started on 2021-10-23.80 UT, and 13 unfiltered frames were collected with exposure time of 60 seconds each. In order to reduce the contamination from the bright background flux of the M31 disk, a reference image taken previously with the same telescope and setup was subtracted from the spatially registered, median-combined CCD frames. The transient was found on the subtracted frame at. R.A. = 00:43:14.53, Dec. = +41:21:09.9 (J2000). No source was detected at this position on the frames taken on 2021-10-18.8 UT and before.
Aperture photometry of the transient was tied to r-band AB-magnitudes of local comparison stars taken from the Pan-STARRS (PS1) DR2 data release. We measure the following (unfiltered) magnitudes on the discovery frame and subsequent follow-up frames:
UT Date Magnitude (error)
2021-10-23.8 17.407 (0.026)
2021-10-24.8 17.119 (0.034)
2021-10-25.8 17.840 (0.035)
A classification spectrum was taken with the BFOSC spectrograph on the 2.16m telescope at Xinglong Observatory on 2021-10-25.67 UT. The exposure time was 1 hour. The spectrum, which covers the region
between 3900 and 8800 Angstrom with a resolution of 2.8 Angstrom/pixel, shows a blue continuum with prominent, narrow Balmer lines having P Cygni profiles, suggesting that the transient is indeed a classical nova in M31. We get v = 1700 km/s expansion velocity from the absorption minimum of the H-alpha feature, which is consistent with the classification.
