GRB 201015A: from seconds to months of optical monitoring and supernova discovery

We present full photometric coverage and spectroscopic data for soft gamma-ray burst GRB 201015A with a redshift z = 0.426. Our data span a time range of 85 d following the detection of GRB. These observations revealed an underlying supernova SN 201015A with a maximum at 8.54 +/- 1.48 d (rest frame) and an optical peak absolute magnitude -19.45(-0.47)(+0.85) mag. The SN stands out clearly, since the contribution of the afterglow at this time is not dominant, which made it possible to determine SN's parameters. A comparison of these parameters reveals that the SN 201015A is the earliest (the minimum T-max) known SN associated with GRBs. Spectroscopic observations during the SN decay stage showed broad lines, indicating a large photospheric velocity, and identified this SN as a Type Ic-BL. Thus, the SN 201015A associated with the GRB 201015A becomes the 27th SN/GRB confirmed by both photometric and spectroscopic observations. Using the results of spectral analysis based on the available data of Fermi-GBM experiment, the parameters E-p,E-i = 20.0 +/- 8.5 keV and E-iso = (1.1 +/- 0.2) x 10(50) erg were obtained. According to the position of the burst on the E-p,E-i-E-iso correlation, GRB 201015A was classified as a type II (long) GRB, which was also confirmed by the T-90,T-i-EH diagram.