M31N 2019-09d and M31N 2022-03d are Confirmed as the Second and Third Observed Eruptions of the Recurrent Nova M31N 2017-01e

ATel #15729; A. W. Shafter (SDSU), K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), Jingyuan Zhao, Tianyu Tu, Jianlin Xu, Mi Zhang, Jiangao Ruan, Guoyou Sun, Yi Ding, Xing Gao (Xingming Observatory)
on 29 Oct 2022; 18:13 UT
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)

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The M31 novae M31N 2019-09d and M31N 2022-03d were discovered through a citizen science program called the Popular Supernova Project (PSP), and announced here and here.

The positions of these novae led the PSP group to conclude that they were both recurrences of the known nova M31N 2017-01e discovered by K. Itagaki in 2017.

Here, we report a careful registration of images of M31N 2019-09d and 2022-03d taken on 2019 Sep 22.645 UT and 2022 Mar 05.592 UT, respectively, with each other, and with an image of the 2017 eruption, M31N 2017-01e, obtained by K. Itagaki on 2017 Jan 31.395 UT. The comparison images reveal that the eruptions are spatially coincident to better than 0.8" for the 2017-2019 pair, and 1.2" for the 2019-2022 pair (see the link to the comparison image below). Given the location of the novae at a distance of 41.5' from the center of M31 (where the observed nova rate is low), the probability of a chance positional coincidence of unrelated novae is negligible. Thus, we confirm that M31N 2019-09d and 2022-03d are indeed the second and third reported eruptions of the recurrent nova M31N 2017-01e. We note that spectroscopic observations of M31N 2017-01e during its 2017 eruption (ATel #10042) revealed it to be a member of the He/N spectroscopic class (see Williams 1992, AJ, 104, 725), which is also consistent with its identification as a recurrent nova.

Timings of the three known outbursts indicate likely recurrence time of 930±20 days (2.55±0.05 yr), which is the second shortest known after M31N 2008-12a. The next eruption of M31N 2017-01e is predicted to occur around September 2024.

Here, we also report additional magnitudes and limits for M31N 2019-09d and M31N 2022-03d obtained using the PSP Celestron 36-cm f/6.9 Schmidt-Cassegrain telescope and the Half-Meter Telescope (HMT), respectively, at Xingming Observatory:

 
     Nova     |    Date [UT]    |   Mag    |    Filter 
 
M31N 2019-09d   2019 09 21.5718   <18.0           CV 
M31N 2019-09d   2019 09 22.6446   17.7±0.1        CV 
M31N 2019-09d   2019 09 24.6424   18.7±0.3        CV 
M31N 2019-09d   2019 09 25.5960   <18.0           CV 
M31N 2019-09d   2019 09 27.6624   <19.0           CV 
 
M31N 2022-03d   2022 03 02.6107   <18.5           CV 
M31N 2022-03d   2022 03 05.5924   17.9±0.1        CV 
 

Further observations of the extremely short recurrence time nova during its anticipated eruption in the latter half of 2024 are strongly encouraged.

Comparison image