Confirmation that M31N 2026-04c is the fourth reported eruption of the recurrent nova 1960-12a

ATel #17788; K. Hornoch (Ondrejov), A. W. Shafter (SDSU), H. Kucakova (Ondrejov), M. Myslivec (HVBO, Czech Republic)
on 9 May 2026; 22:18 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)

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As reported in ATel #17765, M31N 2026-04c was deemed a very likely an outburst of the known recurrent nova M31N 1960-12a. To confirm it, we have carefully registered our co-added 5400-s R-band CMOS image taken on 2026 Apr. 24.042 UT with the 0.4-m telescope at Belec nad Orlici with a co-added 1080-s R-band CCD frame of M31N 2013-05b (the second recorded eruption of the known recurrent nova M31N 1960-12a (= 2013-05b = 2019-07a) taken on 2013 May 29.033 UT with the 0.65-m telescope at Ondrejov.

It reveals that the transients are spatially coincident to of order 0.5" (see the link to the comparison image below).

The probability of a chance positional coincidence of two unrelated novae with observed separation s ~ 0.5" at this position in M31 is p = 0.0054. We conclude that M31N 2026-04c is indeed the fourth reported eruption of the recurrent nova 1960-12a.

In addition to the initial photometry published in ATel #17764, we also report additional magnitudes obtained using the 0.65-m telescope at Ondrejov (D65) and the 0.4-m telescope at Belec nad Orlici (HVBO):

 
  Date [UT]    |  Mag   | Err  | Filter  | Telescope 
 
2026-04-26.066 |  16.3  | 0.15 | Ha      | HVBO 
2026-04-26.095 |  17.7  | 0.15 | R       | D65 
2026-04-29.091 |  19.0  | 0.3  | R       | D65 
2026-04-30.061 |  17.7  | 0.2  | Ha      | HVBO 
2026-05-01.094 |  19.4  | 0.3  | R       | D65 
2026-05-02.091 |  20.4  | 0.4  | R       | D65 
 

A linear least squares fit to the complete light curve (assuming maximum light at R = 16.2) yields t2 = 3.9 +/- 0.4 days, which is slightly shorter than the estimate of t2 = 4.7 days from Clark et al. (2024, ApJS, 272, 28). The latter determination did not include maximum light, and likely underestimated the initial rate of decline.

Comparison Image: M31N 2026-04c (white); M31N 2013-05b (black)