2023MNRAS.521.5207T

We present optical photometric and spectroscopic studies of three supernovae (SNe): SN 2013bz, PSN J0910 + 5003, and ASASSN-16ex (SN 2016ccj). UV-optical photometric data of ASASSN-16ex obtained with the Swift Ultraviolet/Optical Telescope (UVOT) are also analysed. These objects were initially classified as 09dc-like type Ia SNe. The decline-rate parameters (Δm₁₅(B)_true) are derived as 0.92 ± 0.04 (SN 2013bz), 0.70 ± 0.05 (PSN J0910 + 5003), and 0.73 ± 0.03 (ASASSN-16ex). The estimated B-band absolute magnitudes at maximum, -19.61 ± 0.20 mag for SN 2013bz, -19.44 ± 0.20 mag for PSN J0910 + 5003, and -19.78 ± 0.20 mag for ASASSN-16ex, indicate that all three objects are relatively bright. The peak bolometric luminosities for these objects are derived as $\log L_\text{bol}^\text{max} =$ 43.38 ± 0.07, 43.26 ± 0.07, and 43.40 ± 0.06 erg s^–1, respectively. The spectral and velocity evolution of SN 2013bz is similar to that of a normal SN Ia, hence it appears to be a luminous, normal type Ia supernova. On the other hand, the light curves of PSN J0910 + 5003 and ASASSN-16ex are broad and exhibit properties similar to 09dc-like SNe Ia. Their spectroscopic evolution shows similarity with 09dc-like SNe: strong C II lines are seen in the pre-maximum spectra of these two events. Their photospheric velocity evolution is similar to SN 2006gz. Further, in the UV bands, ASASSN-16ex is very blue, like other 09dc-like SNe Ia.