AT2020xyv (PNV J00423733+4120519, M31N 2020-10e) is Not a Recurrence of M31N 1998-10b
ATel #14143; K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), A. W. Shafter (SDSU), T. A. Rector (U. of Alaska, Anchorage), H. Kucakova (Ondrejov), M. Wolf (Astronomical Institute, Charles U., Prague, Czech Republic)
on 3 Nov 2020; 19:35 UT
Credential Certification: Allen W. Shafter (ashafter@sdsu.edu)
Subjects: Optical, Nova, Transient
In Atel #14117 we made a case that AT2020xyv (PNV J00423733+4120519, M31N 2020-10e) was a likely recurrence of M31N 1998-10b based on the proximity of their positions, the location of the objects in M31, and the rapid rise time and spectroscopic classification of AT2020xyv.
As described in Atel #14117, confirmation of the recurrent nova nature of the object awaited a precise astrometric comparison between images of the two novae. We have now located discovery images of M31N 1998-10b: specifically, three H-alpha images from 1998 Oct. 15th, 31st, and Nov. 11th taken by T. A. Rector et al. using the 0.91-m telescope at KPNO during the RBSE.
Because the image from 1998 Oct. 31st has relatively poor S/N ratio, we compared position of the M31N 1998-10b in the two images from 1998 Oct. 15th and Nov. 11th with position of M31N 2020-10e in co-added images taken on 2020 Oct. 22nd and 24th with the 0.65-m telescope at Ondrejov. The result is seen in an
aligned image
constructed from 1998 Nov. 11th (M31N 1998-10b) and 2020 Oct. 22nd (M31N 2020-10e) images. Very similar results were obtained from the other three combinations of the images.
Although very close, it is apparent that the two objects are not, in fact, spatially coincident
(their images are separated by ~1 arcsec), and thus they are two distinct novae. This surprising result has caused us to go back and re-examine the extremely low probability of a chance positional coincidence reported in Atel #14117. Indeed, we found a numerical error in our earlier calculation, with the correct calculation resulting in a value of 4%, which although still quite small, is more easy to reconcile with our current findings.
Finally, we would like to make two additional updates regarding M31N 2020-10e: (1) Based on R-band photometry (partly unpublished) obtained with the 0.65-m telescope at Ondrejov, we have been able to determine a t2 parameter of 4.3 ± 0.5d (assuming Mmax of 16.45 mag on Oct. 22.7 UT), placing M31N 2020-10e among the fastest novae. (2) We would like to note that the M31N 2020-10e was independently discovered by A. Catapano et al., see here.
