Optical light curve parameters of the M31 recurrent nova M31N 2006-11c during its 2015 outburst

ATel #7142; K. Hornoch (Astronomical Institute, Ondrejov, Czech Republic), H. Kucakova, J. Vrastil (Astronomical Institute, Charles U., Prague, Czech Republic), M. Henze (ESAC/ESA), A. F. Valeev, S. Fabrika (Special Astrophysical Observatory, Nizhnij Arkhyz), A. W. Shafter (SDSU), G. Sala, J. Jose, J. Figueira (UPC-IEEC), M. Hernanz (CSIC-IEEC), W. Pietsch (MPE)
on 25 Feb 2015; 18:29 UT
Credential Certification: Allen W. Shafter (aws@nova.sdsu.edu)

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We obtained photometric observations of the recent M31 nova candidate PNV J00413317+4110124 (tentative name: M31N 2015-02b; ATel #7113). The object was subsequently identified as a likely recurrent nova (previous outburst: M31N 2006-11c; see ATel #7116). A comparison image of the aligned (and scaled) discovery images of M31N 2006-11c and M31N 2015-02b (both taken with the 0.65-m telescope at Ondrejov) clearly demonstrates the spatial coincidence of both objects.

We used the 0.65-m telescope at Ondrejov on three nights and obtained the following magnitudes: 2015 Feb. 19.838 UT, R = 16.54 ± 0.05; Feb. 20.733, R = 17.90 ± 0.07; Feb. 20.742, V = 18.56 ± 0.08; Feb. 20.751, I = 17.51 ± 0.10; Feb. 20.818, R = 17.97 ± 0.08; Feb. 20.879, R = 18.00 ± 0.08; Feb. 21.732, R = 18.55 ± 0.09.

To cover the light curve decay we used the Russian 6-m BTA telescope equipped with the SCORPIO spectrograph during two nights yielding the following magnitudes: Feb. 21.641, V = 19.2 ± 0.15; Feb. 21.643, R = 18.45 ± 0.06; Feb. 21.644, B = 19.8 ± 0.15; Feb. 22.690, R = 19.4 ± 0.15.

The field around the nova was also observed with two 4x200s stacked R-band CCD images that were obtained with a Finger Lakes PL4240-1-BI CCD Camera on the 80 cm Ritchey-Chretien F/9.6 Joan Oro telescope at Observatori Astronomic del Montsec, which is owned by the Catalan Government and operated by the Institut d'Estudis Espacials de Catalunya, Spain. The observations were part of an ongoing monitoring campaign for novae in the disk of M31. Nothing was detected at the nova position on 2015 Feb. 18.81 UT with an upper limit of R > 20 mag. This constrains the outburst date significantly better than previous upper limits (ATel #7113). Observations during the subsequent night (2015 Feb. 19.81 UT) showed the object at a magnitude of R = 16.6 ± 0.1 mag.

Photometry from all three telescopes is based on magnitudes of comparison stars taken from the Local Group Galaxies Survey (LGGS, Massey et al. 2006, AJ, 131, 2478).

Using all available R-band photometry from the current eruption we derive the light curve linked below. From the light curve we find t_2(R) = 1.9 ± 0.2 days and t_3(R) = 3.0 ± 0.4 days, assuming Rmax = 16.54 mag on Feb. 19.838 UT. If the nova reached an even higher maximum brightness slightly later, t_2(R) would be even shorter, but values < 1.2 days look unlikely. These decay times classify the 2015 outburst of M31N 2006-11c as "very fast", which is consistent with the t_2(R) of 3-7 days estimated for the 2006 outburst (ATel #7116).

R-band Light Curve