transient’s location, however, our NUV NCR analysis would indicate the host, and the loca- tion of SN 2008ge has undergone moderately recent SF.
Two of the SN 2002cx-like transients show spectral evidence for helium. Taken together with the young environment found for these events,Foley et al. (2013) suggest this as possible evidence for their origin from a helium star accretion on to a WD. However, a helium layer may also form following hydrogen accretion and burning into helium on a WD (Cassisi et al.,
1998; and references therein). It is therefore concluded that although the existence of helium in even a small fraction of these events is a potentially important clue for their origin, its interpretation is still inconclusive.
3.10
Summary
The investigations presented here of the environments and host types of Ca-rich transients show a lack of association with recent SF (similar to that of SNe Ia), and thus point to old progenitor systems, consistent with helium-shell detonation on low mass C/O WDs, and inconsistent with a CCSN origin. Conversely, SN 2002cx-like transients are well matched by young progenitors (< 100 Myr lifetime and likely to be 30–50 Myr) through a close
association to NUV emission and an association to very recent SF that is similar to that displayed by SNe IIP. Such young progenitors are less favourable to failed detonations of Chandrasekhar mass C/O WDs, and more consistent with either the core-collapse of a 7- 9 M⊙ star, or a WD explosion following the accretion of helium star. While the failed
detonation model for these events appears to be consistent with the observable parameters of SN 2002cx-like events themselves, the latter two models currently lack an actual detailed study. Therefore, they can not yet be adequately compared with observations, beyond the generally consistent aspects of their expected environments as studied here.
Chapter 4
Creating and modelling the bolometric
light curve of SN 2012bz
Abstract
The bolometric light curve of a SN is a powerful tool to investigate the nature of the explosion since it contains the entire kinetic energy output of the SN (modulo non-electromagnetic sources, e.g. neutrinos, which can account for 99 per cent of the energy). As such bolometric light curves often form a tight constraint for any modelling of SNe.
In this chapter the gamma-ray-burst-SNe (GRB-SNe) phenomenon will be introduced and specifically the recent case of GRB120422A/SN 2012bz. The bolometric light curve of SN 2012bz is created through the integration of spectral energy distributions based on broad- band photometry with a correction for the missing near-infrared regime based on another GRB-SN, SN 2010bh. An analytical model for bolometric light curves of stripped-envelope SNe is briefly introduced and used to model SN 2012bz. Despite being an unremark- able GRB in cosmological terms, SN 2012bz was very luminous by SN standards (exclud- ing SLSNe), brighter than SN 1998bw and an inferred MNi amongst the largest for SNe (∼ 0.6 M⊙). A comparison of the results of this modelling is made against those found with
more involved spectral analysis performed by others, with generally good agreement found.
4.1. GRB-SNe and the case of GRB120422A/SN 2012bz 80
4.1
GRB-SNe and the case of GRB120422A/SN 2012bz
The link between long GRBs (LGRBs; i.e. those bursts with gamma ray emission>2 sec-
onds) and CCSNe is well established both theoretically and observationally. Proposed under the ‘collapsar’ model of Woosley(1993), the collapse of a massive star can create a stellar mass black hole with an accretion disc. The accretion onto the black hole (the central en- gine) powers a relativistic jet which penetrates the outer layers of the star, producing narrow, beamed emission of gamma rays, most likely due to colliding shells of differing Lorentz factor within the relativistic jet (the exact emission mechanism for the gamma rays is an area of ongoing study, for a recent review see M´esz´aros, 2013). The duration of this emission is intrinsically linked to the time-scale of the central engine and this is thought to depend somewhat on the size of the collapsing star, where a larger sized collapsing body will fuel the central engine for a longer duration.
Observational support arrived in the error box of the very low redshift GRB980425, where an emerging SN was seen to be brightening temporally coincident with this burst (Galama et al., 1998). The SN, SN 1998bw, was very luminous and classified as a SN Ic-BL, due to the very high photospheric velocity it exhibited (resulting in broad-line features in its spectra). The observational association has been cemented, withHjorth and Bloom (2012) counting 11 objects with good light curve, and at least some spectroscopic, evidence for a SN in the light curve of a GRB afterglow (not including the very recent examples SN 2012bz,
Melandri et al. 2012;Schulze et al. 2014; SN 2013cqXu et al. 2013and SN 2013dx Cenko et al., in prep). In each case that a classification is possible, the identified SN has been of type Ic-BL. Previous studies comparing GRBs that have an observed SN to ‘cosmological’ GRBs (i.e. those at high redshift, or where no SN was detected) appeared to show to a bias towards lower luminosity for GRBs that show a SN (Guetta and Della Valle,2007), with the notable exception of GRB030329/SN 2003dh (Stanek et al.,2003).
However, Xu et al. (2013) present GRB 130427A/SN 2013cq – with the GRB bring ex- tremely luminous even for cosmological GRBs, despite its moderate redshift ofz = 0.3399.
Coupled with GRB030329, this would suggest there is in fact a common progenitor system for GRB-SN to those GRB at high redshift, and high explosion energy events are capable of