SN 2008gz - most likely a normal Type IIP event

Abstract

We present BVRI photometric and low‐resolution spectroscopic investigation of the Type II core‐collapse supernova (SN) 2008gz, which occurred in a star‐forming arm and within a half‐light radius (solar metallicity region) of the nearby spiral galaxy NGC 3672. The SN event was detected late, and a detailed investigation of its light curves and spectra spanning 200 d suggest that it is an event of Type IIP similar to the archetypal SNe 2004et and 1999em. However, in contrast to other events of its class, SN 2008gz exhibits a rarely observed V magnitude drop of 1.5 over the period of a month during the plateau to nebular phase. Using an AV of 0.21 mag as a lower limit and a distance of 25.5 Mpc, we estimate a synthesized 56Ni mass of 0.05 ± 0.01 M⊙, a mid‐plateau MV of −16.6 ± 0.2 mag and a total radiant energy of ∼1049 erg. The photospheric velocity is observed to be higher than observed for SN 2004et at similar epochs, indicating that the explosion energy was comparable to or higher than that of SN 2004et. A similar trend was also seen for the expansion velocity of H envelopes. By comparing the properties of SN 2008gz with other well‐studied events, as well as by using a recent simulation of pre‐SN models by Dessart, Livne & Waldman, we infer an explosion energy range of 2–3 × 1051 erg, and this coupled with the observed width of the forbidden [O i] 6300–6364 Å line at 275 d after the explosion gives an upper limit for the main‐sequence (non‐rotating, solar metallicity) progenitor mass of 17 M⊙. Our narrow‐band Hα observation, taken nearly 560 d after the explosion, and the presence of an emission kink at zero velocity in the Doppler‐corrected spectra of SN indicate that the event took place in a low‐luminosity star‐forming H ii region.

Measuring expansion velocities in Type II-P supernovae

“…Recently, Roy et al (2011) published a study of velocity measurement for the Type II-P SN 2008gz. They applied a similar technique of using SYNOW to fit Fe II features around 5000 Å.…”

Discovery of a Red Quasar With Recurrent Activity

“…First we use the empirical relation, developed from the study of spectra of nearby supernovae (e.g. Barbon et al 1990;Turatto et al 2003;Roy et al 2011;Poznanski et al 2012), between the width of the Na I D absorption dip and the host reddening. This has been used widely to determine the host galaxy extinction directly from the observed spectrum.…”

SN 2008in—BRIDGING THE GAP BETWEEN NORMAL AND FAINT SUPERNOVAE OF TYPE IIP

“…To improve the S/N ratio and optimize the sampling, the observations were carried out in a binned mode of 2×2 pixel. 20 IRAF stands for Image Reduction and Analysis Facility distributed by the National Optical Astronomy Observatory which is operated by the Association of Universities for research in Astronomy, Inc. under co-operative agreement with the National Science Foundation 21 DAOPHOT stands for Dominion Astrophysical Observatory Photometry (Stetson 1987) by Roy et al (2011). Bias subtraction and flat fielding were performed on the raw frames and the cosmic removal was done using LACOSMIC routine (van Dokkum 2001).…”

“…As the SN lies in the outskirts of the galaxy on a relatively faint and smooth background, the photometry at the initial phases (mostly during the plateau phase when the SN is bright) is estimated using the profile fitting method. During nebular phases, when the SN becomes faint, the true SN flux is estimated using the galaxy template subtraction method following the procedures of Roy et al (2011). As a galaxy template, we used post-explosion (+600d) images observed on 2011 January 04 under good seeing conditions.…”

“…This contribution has been accounted for while measuring the net U V OIR flux. It has been assumed that contribution in the U band The black filled circle shows the estimated value of mid-plateau photospheric velocity, calculated using the relation mentioned in Roy et al (2011). The right panel shows a comparison of velocity derived from Hα with that of low-luminosity event like SN 2005cs (Pastorello et al 2009) and normal Type IIP SNe 1999em ) and 2004et (Sahu et al 2006).…”