The bright Type IIP SN 2009bw, showing signs of interaction★

Abstract

We present photometry and spectroscopy of the Type IIP supernova (SN IIP) 2009bw in UGC 2890 from a few days after the outburst to 241 d. The light curve of SN 2009bw during the photospheric phase is similar to that of normal SNe IIP but with a brighter peak and plateau ( mag, mag). The luminosity drop from the photospheric to the nebular phase is one of the fastest ever observed, ∼2.2 mag in about 13 d. The radioactive tail of the bolometric light curve indicates that the amount of ejected 56Ni is ≈0.022 M⊙. The photospheric spectra reveal high‐velocity lines of Hα and Hβ until about 105 d after the shock breakout, suggesting a possible early interaction between the SN ejecta and pre‐existent circumstellar material, and the presence of CNO elements. By modelling the bolometric light curve, ejecta expansion velocity and photospheric temperature, we estimate a total ejected mass of ∼8–12 M⊙, a kinetic energy of ∼0.3 foe and an initial radius of ∼3.6–7 × 1013 cm.

Supersolar Ni/Fe production in the Type IIP SN 2012ec

“…Subtracting this artificial B-template from the measured B magnitudes gave estimates for the SN of B = 19.36 mag at 187d and B = 19.50 mag at 202d. The resulting B − V colours of the SN are similar to other Type IIP SNe (Maguire et al 2010;Inserra et al 2012Inserra et al , 2013Tomasella et al 2013).…”

Moderately luminous Type II supernovae

“…This line was also identified in other type II SNe (e.g. SN 1992H, SN 2007od, SN 2009bw;Inserra et al 2011Inserra et al , 2012a, and references therein). The middle feature is probably Fe ii λ6456 but the line strength would indicate a much higher optical depth than usual for metal lines at this stage.…”

“…At this stage also SN 2009bw andSN 1999em show HV Hα at ∼7300 km s −1 (Inserra et al 2012a) and ∼8200 km s −1 (Chugai et al 2007), respectively. The weak HV Hα components of SN 2009dd and SN 1996W appear at velocity ∼13800 and ∼11500 km s −1 , respectively, remaining steady during the early phases.…”

“…To our knowledge, similar features have not been seen in other type II SNe (at least with this strength). The bluest component was identified with Si ii λ6355 as in SN 2007od (Inserra et al 2011(Inserra et al , 2012b and SN 2009bw (Inserra et al 2012a). The central component might be a HV feature of Hα with v = 13800 km s −1 or, alternatively, Fe ii λ6456 with an unusually high optical depth.…”

“…Recently also a few SNe with overall normal spectral features have shown weak but unequivocal evidence of ejecta-CSM interaction from early times, reviving the interest for the studies of interacting SNe. Among them we recall the type IIP SNe 1999em and 2004dj (Chugai et al 2007) or the atypical type II SN 2007od (Inserra et al 2011) and SN 2009bw (Inserra et al 2012a), the last two belonging to the bright tail of the type IIP SN luminosity distribution.…”