M31N 2026-08a is the third reported eruption of the recurrent nova M31N 2006-11c

ATel #17941; K. Hornoch (Ondrejov), F. Castellani (Monte Baldo Observatory, Italy), A. W. Shafter (SDSU), P. Zasche (Charles U.)
on 4 Aug 2026; 23:27 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)

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F. Castellani et al. reported the discovery of a probable nova in M31. The nova, designated as AT 2026wvv, was detected on a co-added 3600-s unfiltered CCD image taken with a 0.40-m f/7 Dall-Kirkham telescope at Monte Baldo Observatory, Ferrara di Monte Baldo, Verona, Italy. F. Castellani et al. pointed out that the object is located only 0.68" from the position of the recurrent nova M31N 2006-11c (see ATel #7113, ATel #7116, ATel #7142, and ATel #7158) and that it is likely another eruption of the known recurrent nova.

Following the standard CBAT designation scheme we designate the object AT 2026wvv as M31N 2026-08a.

To confirm a spatial coincidence of M31N 2026-08a with M31N 2006-11c = 2015-02b, we carefully registered a co-added 780-s R-band CMOS image of M31N 2026-08a taken on 2026 Aug. 3.867 UT with the 0.65-m telescope at Ondrejov with a co-added 600-s R-band CCD image of M31N 2015-02b taken on 2015 Feb. 19.733 UT with the same telescope. The comparison image (see the link to the image below) clearly demonstrates the spatial coincidence of both objects to of order 0.5".

The probability of a chance positional coincidence of two unrelated novae with observed separation s ~ 0.5" at this position in M31 (semi-major axis of a=19.8' from the nucleus) is p=0.0003. We conclude that M31N 2026-08a is indeed the third reported eruption of the recurrent nova M31N 2006-11c.

The interval between the first two observed eruptions was ~8.2 yr and that between the second and the third observed eruption is ~11.5 yr. Assuming that we did not miss any eruptions since 2006, the mean recurrence period is ~9.9 ± 2.3 yrs.

We also report photometry of the current eruption obtained using the 0.40-m telescope at Monte Baldo (MBO) and the 0.65-m telescope at Ondrejov (D65):

 
  Date [UT]    |  Mag   | Err  | Filter     | Telescope 
 
 
2026-08-02.891 |  17.1  | 0.2  | Unfiltered | MBO 
2026-08-03.867 |  18.15 | 0.1  | R          | D65 
2026-08-03.888 |  18.6  | 0.3  | Unfiltered | MBO 
2026-08-04.870 |  18.9  | 0.3  | Unfiltered | MBO 
2026-08-04.898 |  18.8  | 0.15 | R          | D65 
 

Comparison Image: M31N 2015-02b (white); M31N 2026-08a (black)