  M31N 2015-01a (or M31LRN 2015) is a red nova that erupted in January 2015 --
the first event of this kind observed in M31 since 1988. Very few similar
events have been confirmed as of 2015. Most of them are considered to be
products of stellar mergers. Results of an extensive optical monitoring of the
transient in the period January-March 2015 are presented. Eight optical
telescopes were used for imaging. Spectra were obtained on BTA, GTC and the
Rozhen 2m telescope. We present a highly accurate 70 d lightcurve and
astrometry with a 0.05" uncertainty. The color indices reached a minimum 2-3 d
before peak brightness and rapidly increased afterwards. The spectral type
changed from F5I to F0I in 6 d before the maximum and then to K3I in the next
30 d. The luminosity of the transient was estimated to
$8.7^{+3.3}_{-2.2}\times10^{5}L_{\odot}$ during the optical maximum. Both the
photometric and the spectroscopic results confirm that the object is a red
nova, similar to V838 Monocerotis.
