Optical spectra of type Ia SN 2015bq

This SN reaches a B-band absolute magnitude at M_B_=-19.68+/-0.41mag and a peak bolometric luminosity at L=(1.75+/-0.37)x10^43^erg/s, with a relatively small post-maximum decline rate [{Delta}m_15_(B)=0.82+/-0.05mag]. The flux excess observed in the light curves of SN 2015bq a few days after the explosion, especially seen in the UV bands, might be due to the radioactive decay of ^56^Ni mixed into the surface.

The radiation from the decay of the surface ^56^Ni heats the outer layer of this SN. It produces blue U-B color followed by monotonically reddening in the early phase, dominated iron-group lines, and weak intermediate-mass element absorption features in the early spectra. The scenario of enhanced ^56^Ni in the surface is consistent with a large amount of ^56^Ni (M_56Ni_=0.97+/-0.20M_{sun}_) synthesized during the explosion.