One year of monitoring of the Type IIb supernova SN 2011dh

Optical $UBVRI$ photometry and low resolution spectroscopy of the type IIb supernova SN 2011dh in M51 are presented, covering the first year after the explosion. The light curve and spectral evolution are discussed. The early phase light curve evolution of SN 2011dh is very similar to SN 1993J and SN 2008ax. In the late phase, however, SN 2011dh declines faster than SN 1993J. The late phase decline in the $B$-band is steeper than in the $R$ and $I$ bands, indicating the possibility of dust formation. With a peak $V$-band absolute magnitude of $M_V = -17.123\pm0.18$ mag, SN 2011dh is a marginally faint type IIb event. The reddening corrected colour curves of SN 2011dh are found to be redder than other well studied type IIb supernovae. The bolometric light curve indicates $\sim$ 0.09 M$_\odot$ of $^{56}$Ni is synthesized during the explosion. The HeI lines were detected in the spectra during the rise to maximum. The nebular spectra of SN 2011dh show a box shaped emission in the red wing of the [OI] 6300-6363 \AA\ feature, that is attributed to H$\alpha$ emission from a shock excited circumstellar material. The analysis of nebular spectra indicates that $\sim 0.2$ M$_\odot$ of oxygen was ejected during the explosion. Further, the [CaII]/[OI] line ratio in the nebular phase is $\sim$ 0.7, indicating a progenitor with a main sequence mass of 10-15 M$_\odot$.Comment: Accepted for publication in MNRA

Supernova SN 2012dn: A spectroscopic clone of SN 2006gz

We present optical and UV analysis of the luminous type Ia supernova SN 2012dn covering the period $\sim -$11 to +109 days with respect to the $B$ band maximum, that occurred on JD 2456132.89 $\pm$ 0.19, with an apparent magnitude of $m_{B}^\text{max}$ = 14.38 $\pm$ 0.02. The absolute magnitudes at maximum in $B$ and $V$ bands are $M_{B}^\text{max} = -19.52 \pm 0.15$ and $M_{V}^\text{max} = -19.42 \pm 0.15$, respectively. SN 2012dn is marginally luminous compared to normal type Ia supernovae. The peak bolometric luminosity of $\log L_\text{bol}^\text{max} = 43.27 \pm 0.06$ erg s$^{-1}$ suggests that $0.82 \pm 0.12$ M$_\odot$ of $^{56}$Ni was synthesized in the explosion. The decline rate $\Delta m_{15}(B)_\text{true}= 0.92 \pm 0.04$ mag is lower than that of normal type Ia supernovae, and similar to the luminous SN 1991T. However, the photometric and spectroscopic behaviour of SN 2012dn is different from that of SN 1991T. Early phase light curves in $R$ and $I$ bands are very broad. The $I$ band peak has a plateau-like appearance similar to the super-Chandra SN 2009dc. Pre-maximum spectra show clear evidence of C\,{\sc ii} 6580 \AA\, line, indicating the presence of unburned materials. The velocity evolution of C\,{\ sc ii} line is peculiar. Except for the very early phase ($\sim-$13 d), the C\,{\sc ii} line velocity is lower than the velocity estimated using the Si\,{\sc ii} line. During the pre-maximum and close to maximum phase, to reproduce observed shape of the spectra, the synthetic spectrum code {\sc syn++} needs significantly higher blackbody temperature than those required for normal type Ia events. The photospheric velocity evolution and other spectral properties are similar to those of the carbon-rich SN 2006gz.Comment: Accepted for publication in MNRAS, 19 pages, 20 figure

Optical studies of Type IIb SN 2011dh

UBVRI photometry and low resolution optical spectroscopy of the type IIb SN 2011dh in M51 are presented, covering the first year after the explosion. The peak absolute magnitude in V-band of −17.12±0.18 mag indicates SN 2011dh to be a normal bright type IIb event. The peak quasi-bolometric luminosity indicates that ~ 0.06 M☉ of 56Ni was synthesized in the explosion. The He I lines were detected in the spectra much before the maximum light in B-band. The nebular spectra of SN 2011dh show a box shaped emission in the red wing of [OI] 6300, 6363 line due to Hα emission excited because of shock-wave interaction. The analysis of the nebular spectra indicates a progenitor with a main sequence mass of 10-15 M☉

Photometric and spectroscopic evolution of type II-P supernova SN 2004A

We present optical photometry and spectroscopy of the normal type IIP supernova SN2004A, which was discovered in the galaxy NGC 6207 on 2004 January 9.84UT. Early observations indicated that the supernova was discovered at about two weeks since explosion. We estimate the distance to NGC 6207 to be 20.35 ± 4.5 Mpc using the Standard Candle method. Using this distance, we estimate the ejected nickel mass in the explosion to be 0.032 ± 0.02 M☉. The plateau luminosity, its duration (about 80 days) and the expansion velocity of the supernova ejecta at the middle of the plateau indicate an explosion energy of 4.7 ± 2.7 × 1050 ergs and an ejected envelope mass of 7.2 ± 2.2 M☉. The ejected envelope mass implies a main sequence mass of 10 ± 2.5M☉ for the progenitor

Type Ia supernovae SN 2013bz, PSN J0910+5003 and ASASSN-16ex: similar to 09dc-like?

We present optical photometric and spectroscopic studies of three supernovae (SNe) SN 2013bz, PSN J0910+5003 and ASASSN-16ex. UV-optical photometric data of ASASSN-16ex obtained with Swift-UVOT are also analyzed. These objects were initially classified as 09dc-like type Ia SNe. The decline rate parameters ($\Delta m_{15}(B)_{true}$) are derived as 0.92 $\pm$ 0.04 (SN 2013bz), 0.70 $\pm$ 0.05 (PSN J0910+5003) and 0.73 $\pm$ 0.03 (ASASSN-16ex). The estimated $B$ band absolute magnitudes at maximum: $-$19.61 $\pm$ 0.20 mag for SN 2013bz, $-$19.44 $\pm$ 0.20 mag for PSN J0910+5003 and $-$19.78 $\pm$ 0.20 mag for ASASSN-16ex indicate that all the three objects are relatively bright. The peak bolometric luminosities for these objects are derived as $\log L_\text{bol}^\text{max} =$ 43.38 $\pm$ 0.07 erg s$^{-1}$, 43.26 $\pm$ 0.07 erg s$^{-1}$ and 43.40 $\pm$ 0.06 erg s$^{-1}$, respectively. The spectral and velocity evolution of SN 2013bz is similar to 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 CII 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.Comment: 19 pages, 20 figures, accepted for publication in MNRA