"Emission line models for the lowest mass core-collapse supernovae - I. Case study of a 9 M⊙ one-dimensional neutrino-driven explosion" (Jerkstrand+2018) The first paper coming out of my Marie Curie project at MPA Garching, these are the first models for neutrino-driven supernova simulations. The timing of progress in stellar evolution simulations in the 8-12 Msun range has come together with successful 1D neutrino simulations from this mass range to open up this important mass range (30-50% of all CCSNe) for analysis. In this paper we find that spectral models closely resemble observed spectra form the subluminous IIP class. We also discuss how one can distinguish low-mass iron core explosions from ONeMg-core explossions (electron capture supernovae).
"The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor" (Anderson+2018) A Type II SN with strong metal lines, possibly from the elusive 20-30 Msun range. If so, the fact that it had a very low metallicity has implications for solutions to the Red SuperGiant Problem. It makes it more plausible that the reason we dont see massive RSGs explode is related to metallicity-dependent mass loss, as most events in the local Universe have close to solar metallicity.
Using late-time optical and near-infrared spectra to constrain Type Ia supernova explosion properties (Maguire+2018) Observationally-focused paper on Ia spectra. One development here was to apply the semi-analytic Ni/Fe diagnostic of Jerkstrand+2015 also to thermonuclear explosions. This requires a NLTE correction factor, which we took from standard SUMO runs of W7. Although more detailed methods and more data are needed, the preliminary picture shows close to solar Ni/Fe production in Ia SNe. We now have exciting new results on this ratio both for thermonuclear and core-collapse SNe,and it tells us crucial information about the explosion.
Short-Lived Circumstellar Interaction in the Low-Luminosity Type IIP SN 2016bkv (Hosseinzade+2018) A narrow-lined IIP SN that shows two interesting properties: Strong but short-lived CSI, and a nebular spectrum that looks close to what we expect from electron capture SN models that I recently computed at MPA. Is this the first detected ECSN? We think they come from sAGB stars with heavy mass loss that would give strong CSI, so the puzzle pieces seem to fit.
"Long-duration superluminous supernovae at late times" (Jerkstrand+2017) A breakthrough in our understanding of superluminous SNe from two perspectives. 1) A strong similarity to GRB-SNe was revealed once galaxy contamination was recognized and carefully removed from both old a new data 2) Robustly inferred (largely model-independent) mass constraints on oxygen that points to very massive WR star progenitors. Combined with LIGO results last 2 years (black holes in mass range 15-40 exist and almost certainly imply failed SNe) we now seem faced to explain that massive WR stars sometimes make black holes but sometimes explode as SLSNe or GRB SNe.
SNe 2013K and 2013am: observed and physical properties of two slow, normal Type IIP events (Tomasella+2017) Study of two IIP SNe in the intermediate regime between subluminous and normal. Combining radiation hydrodynamic and nebular modelling gave quite consistent indications of low/intermediate mass progenitors. These new objects are important in highlighting what kind of continuum we expect in explosion properties, as there is a qualitative core structure change around 10-12 Msun that is expected to lead to two groups of properties. However these two objects sit between the two traditional groups questioning this paradigm.
Extremely late photometry of the nearby SN 2011fe (Kerzendorf+2017) With SUMO it was recently demonstrated how fluorescence of UV emissivity completely dominate the optical spectrum of Type Ia SNe at late times. The first main goal of late-time studies is to infer the 57Ni mass (it depends sensitively on the explosion physics), which becomes the power source after ~800d. here we present unique new data on 2011fe in this phase, and discuss how to model this to interpret the 57Ni mass. This is a big challenge as both NLTE, fluorescence, and gas time-dependence turn out to be all important, and we have yet to develop simulation capability that can treat all of these three simultaneously.
The multifaceted Type II-L supernova 2014G from pre-maximum to nebular phase(Terreran+2016) Another IIL SN that, as 2013ej, shows deviation from 56Co rate on the tail, which is still not understood. This SN shows stronger spectroscopic evidence for a high-mass origin than 2013ej. We employed the new Ni/Fe diagnosti method from Jerkstrand+2015, and this SN falls in the ~3 times supersolar regime that suggests burning and ejection of silicon layers have taken place.
"450d of Type II SNe 2013ej in optical and near-infrared (Yuan+2016) Study of a Type IIL SN, a class for which several basic properties remain to be understood. Often hypothesized to come from more massive stars than IIP, which would lead to more mass loss and faster declining LC, here we found that emission lines from nucleosynthesis products were moderately strong and more indicated a medium-mass progenitor.
"The Diversity of Type II Supernova vs. The Similarity in Their Progenitors" (Valenti+2016) First quantitative study of late-time spectra of Type IIL SNe. We find similar oxygen line strengths as in the Type IIP class, and thus no suggestion that Type IIL SNe would come from a higher-mass population.
PTF12os and iPTF13bvn. Two stripped-envelope supernovae from low-mass progenitors in NGC 5806 (Fremling+2016) Type IIb SNe have rapidly gone from being considered an obscure and rare subclass to now being assessed as quite common (>~10%)and perhaps best understood SN class. These SNe have traces of hydrogen. A few years ago the first model grids were developed for them, and strongly indicated an origin in low-mass stars, implying the mass loss must be due to Roche lobe overflow. Here this hypothesis was further strengthened by modelling of more data. It also highlight issues with understanding what truly distinguishes Type IIB from Type Ib supernovae.
"Reconciling the Infrared Catastrophe and Observations of SN 2011fe" (Fransson & Jerkstrand, ApJL 2015) The first spectral models of a Type Ia SN at very late times (1000d) are compared with observations of SN 2011fe. Type Ia SNe have highly complex behaviour at very late times (>~600d). They get so cold that all thermal emission shifts into the IR. At the same time, they get more neutral which leads to more non-thermal excitation and UV emission. This UV emission in turn fluoresces into the optical, replacing the thermal emission. Thus, the mechanism for forming the optical spectrum completely changes. Modeling this properly is crucial to infer the 57Ni mass. This particular application illustrates an interesting point about modelling; adding more effects is not a mono-tonic path to improved predictions. In fact, models a few years ago added non-thermal excitation, but had no fluorescence. This gave worse UV and optical predictions than models without either effect. One needs both of these to make the model actually improve.
"SN 2015bn: a detailed multi-wavelength view of a nearby super luminous supernova" (Nicholl+2016, ApJ). Observations of only the third superluminous supernova at late times. The red part of the +250d spectrum shows quite good agreement with PISN models, but the blue part is strongly discrepant. Later-time data of this SN is presented and modelled here.
"Discovery of molecular hydrogen on SN 1987A (Fransson+ 2016, ApJL)" The first discovery of molecular hydrogen in a supernova. The identification was facilitated by comparison with models for the atomic emission.
"Nebular spectra of pair-instability supernovae"(Jerkstrand, Smartt & Heger MNRAS 2015) Pair-instability supernovae are the theorised explosions of very massive stars, M > 100 Msun. In this paper we compute model spectra for three PISN models at low end, middle, and upper end of the mass range (He cores from 80-130 Msun). The physical conditions and emergent spectra between 400-1000d post-explosion are analysed. Comparison with the few suggested candidates so far (SN 2007bi and PTF12dam) shows poor agreement with the models. An important point is, however,that if He cores of mass 70-130 Msun can form and roughly follow a typical IMF at lower mass, most of them will be dim SN explosions. We analyse the low-mass model (He80) to predict spectral signatures to search for among low-luminosity events.
"SN 2009ip at late times - an interacting transient at +2 years" (Fraser+2015) Late-time observations of the unique transient SN 2009ip, which we are not sure whether its a CCSN or a massive non-terminal eruption. Some metal emission lines are seen but we show by comparing with models of solar-abundance gas that this is not necessarily due to newly synthesised material.
Spitzer observations of SN 2014J and properties of mid-IR emission in Type Ia Supernovae Observations of SN 2014J are compared to spectral predictions for the MIR range based on W7 calculations at 130d with SUMO.
"SN 2011fu: a type IIb supernova with a luminous double-peaked light curve"(Morales-Garoffolo+ MNRAS 2015) Study of another IIb SN, with comparison of mass estimates obtained both from light curves modelling (with M. Berstens code) and from nebular modelling. We find reasonable agreement - its yet another low-mass object that must have been stripped by binary interaction.
Constraints on Explosive Silicon Burning in Core-collapse Supernovae from Measured Ni/Fe Ratios Follow-up paper on ''Supersolar Ni/Fe production in the Type IIP SN 2012ec" where we applied nucleosynthesis network simulations to study under what burning conditions the Ni/Fe ratio could be reproduced.
"Supersolar Ni/Fe production in the Type IIP SN 2012ec"(Jerkstrand+ MNRAS 2015) Third paper in the Type IIP series, studying SN 2012ec. While the original aim was to study the oxygen lines, the paper took another turn as SN 2012ec turned out to have highly unusual nickel lines ([Ni II] 7378 and [Ni II] 1.939 mum). These lines may be used to show that a high production of stable nickel has occurred (mass 6E-3 Msun). The paper also presents a simple analytical technique one may use to determine the Ni/Fe ratio from luminosities in [Ni II] 7378 and [Fe II] 7378. SN 2012ec has a Ni/Fe ratio of over 3 times the solar value.
"The Type IIb SN 2011dh - 2 years of observations and modelling of the light curves" (Ergon, Jerkstrand+,A&A 2015) Companion paper to the one above, some of the model output and analysis presented here, in particular dust discussions.
"Late-time spectral line formation in Type IIb supernovae" (Jerkstrand+, A&A 2015) Modelling of Type IIb SNe, with particular focus on SN 2011dh. The [O I] 6300, 6364 lines constrain the progenitors of SN 1993J, SN 2008ax, and SN 2011dh to the 12-16 Msun range. The paper also studies magnesium line formation, and derives semi-analytical methods to use the Mg I 1.5 mu luminosity combined with the oxygen recombination line luminosities to determine the magnesium mass (0.02 - 0.14 Msun for SN 2011dh). The paper also studies radiative transfer effects; the line blocking of the metal core comes out as a very plausible explanation for the line blue shifts seen on most stripped envelope SNe.
"The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines" (Jerkstrand+, MNRAS 2014) Second paper in Type IIP series. Improvements in the code, addition of a MZAMS = 25 Msun model, and application to SN 2012aw, which we also find to match models close to MZAMS = 15 Msun. An additional technique raised here is the possibility of using [O I] 5577 to constrain the temperature.
"The progenitor mass of the Type IIP SN 2004et from late-time spectral modelling" (Jerkstrand+, A&A 2012) The first paper in a series aimed at analysing the oxygen yields in Type IIP SNe, and from that progenitor masses. Here we study SN 2004et, favouring a progenitor around 15 Msun. We also made detailed modelling of the unique set of MIR spectra available for SN 2004et. We could use the fact that many iron-group MIR lines are in LTE and optically thick to determine the fraction of the core occupied by the 56Ni bubble. This is the only SN apart from SN 1987A for which this has been done. This paper also contains the code developments that lead to the complete coupling of NLTE, radiation transport, and non-thermal effects (see appendices).
"Constraining the physical properties of Type II-Plateau supernovae using nebular phase spectra" (Maguire, Jerkstrand+, MNRAS 2012) Here we looked at a sample of Type IIP SNe in terms of line ratios. This paper also points out that significant fraction of flux in the metal lines often comes from the hydrogen envelope.
"NERO - a post-maximum supernova radiation transport code" (Maurer, Jerkstrand+, MNRAS 2012) In this paper the code developed during my PhD was compared against a similar code called NERO that developed by I. Maurer at MPA around the same time. We found that the codes gave very similar outputs which was an important test.
"The 44Ti-powered spectrum of SN 1987A" (Jerkstrand, Fransson & Kozma, A&A 2011) Code description and application to analyse HST spectrum of SN 1987A at an age of 8 years. Inclusion of radiative transfer in the modelling turns out to be important even at these late epochs. The non-thermal processes produce a lot of UV/blue emissivity that is transported to the optical and NIR by scattering and fluorescence. Indeed a significant part of the spectrum is formed by fluorescence. We also attempted to determine the 44Ti mass, finding a best value of 1.5E-4 Msun. This result was recently (quite spectacularly) confirmed to the exact same estimate by (model-indepedent) observations of the Xray decay lines, a very important validity test for SUMO.
"The 3-D structure of SN 1987A's inner ejecta" (Kjaer+, A&A 2010) Integral Field Spectroscopy of SN 1987A at an age of 20 years, combined with spectral modelling to interpret the line emission. An important find here was the models predict the 3D 1.6 micron map to trace silicon (through [Si I] 1.64 mu) rather than iron (through [Fe II] 1.64 mu)