SN 2012aw Research Articles

Spectropolarimetry of Type II supernovae

We investigate the polarization spectra of hydrogen-rich core-collapse supernovae (Type II SNe). The polarization signal from SNe contains two independent components: intrinsic SN polarization and interstellar polarization (ISP). From these components, we can study the SN explosion geometry and the dust properties in their host galaxies or in the Milky Way. In this first paper, we employ a newly improved method to investigate the properties of the ISP components of 11 well-observed Type II SNe. Our analyses revealed that 10 of these 11 SNe showed a steady ISP component with a polarization degree of ≲1.0%, while one SN was consistent with zero ISP. As for the wavelength dependence, SN 2001dh (and possibly SN 2012aw) showed a non-Milky-Way-like ISP likely originating from the interstellar dust in their respective host galaxies: their polarization maxima were located at short wavelengths (≲4000 Å). Similar results have been obtained previously for highly reddened SNe. The majority of the SNe in our sample had uncertainties in the wavelength dependence of their ISP components that were too large for further consideration. Our work demonstrates that further investigation of the ISP component of the SN polarization, by applying this method to a larger SN sample, can provide new opportunities to study interstellar dust properties in external galaxies.

Quantifying the dust in SN 2012aw and iPTF14hls with ORBYTS

ABSTRACT Core-collapse supernovae (CCSNe) are capable of producing large quantities of dust, with strong evidence that ejecta dust masses can grow significantly over extended periods of time. Red–blue asymmetries in the broad emission lines of CCSNe can be modelled using the Monte Carlo radiative transfer code damocles, to determine ejecta dust masses. To facilitate easier use of damocles, we present a Tkinter graphical user interface (GUI) running damocles. The GUI was tested by high school students through the Original Research By Young Twinkle Students programme, who used it to measure the dust masses formed at two epochs in Type IIP CCSNe, SN 2012aw and iPTF14hls, demonstrating that a wide range of people can contribute to scientific advancement. Bayesian methods quantified uncertainties on our model parameters. From the red scattering wing in the day 1863 Hα profile of SN 2012aw, we constrained the dust composition to large (radius >0.1 μm) silicate grains, with a dust mass of $6.0^{+21.9}_{-3.6}\times 10^{-4}~\mathrm{ M}_\odot$. From the day 1158 Hα profile of SN 2012aw, we found a dust mass of $3.0^{+14}_{-2.5}\times 10^{-4}$ M⊙. For iPTF14hls, we found a day 1170 dust mass of 8.1$^{+81}_{-7.6}\times 10^{-5}$ M⊙ for a dust composition consisting of 50 per cent amorphous carbon and 50 per cent astronomical silicate. At 1000 d post-explosion, SN 2012aw and iPTF14hls have formed less dust than the peculiar Type II SN 1987A, suggesting that SN 1987A may have formed a larger dust mass than typical Type IIP’s.

The explosion of 9–29M⊙stars as Type II supernovae: Results from radiative-transfer modeling at one year after explosion

We present a set of nonlocal thermodynamic equilibrium steady-state calculations of radiative transfer for one-year-old Type II supernovae (SNe) starting from state-of-the-art explosion models computed with detailed nucleosynthesis. This grid covers single-star progenitors with initial masses between 9 and 29M⊙, all evolved with the codeKEPLERat solar metallicity and ignoring rotation. The [O I]λλ6300, 6364 line flux generally grows with progenitor mass, and Hαexhibits an equally strong and opposite trend. The [Ca II]λλ7291, 7323 strength increases at low56Ni mass, at low explosion energy, or with clumping. This Ca IIdoublet, which forms primarily in the explosively produced Si/S zones, depends little on the progenitor mass but may strengthen if Ca+dominates in the H-rich emitting zones or if Ca is abundant in the O-rich zones. Indeed, Si–O shell merging prior to core collapse may boost the Ca IIdoublet at the expense of the O Idoublet, and may thus mimic the metal line strengths of a lower-mass progenitor. We find that the56Ni bubble effect has a weak impact, probably because it is too weak to induce much of an ionization shift in the various emitting zones. Our simulations compare favorably to observed SNe II, including SN 2008bk (e.g., the 9M⊙model), SN 2012aw (12M⊙model), SN 1987A (15M⊙model), or SN 2015bs (25M⊙model with no Si–O shell merging). SNe II with narrow lines and a low56Ni mass are well matched by the weak explosion of 9–11M⊙progenitors. The nebular-phase spectra of standard SNe II can be explained with progenitors in the mass range 12–15M⊙, with one notable exception for SN 2015bs. In the intermediate mass range, these mass estimates may increase by a fewM⊙, with allowance for clumping of the O-rich material or CO molecular cooling.

Parameters of the type-IIP supernova SN 2012aw

ABSTRACT We present the results the photometric observations of the Type IIP supernova SN 2012aw obtained for the time interval from 7 to 371 d after the explosion. Using the previously published values of the photospheric velocities, we have computed the hydrodynamic model which simultaneously reproduced the photometry observations and velocity measurements. We found the parameters of the pre-supernova: radius R = 500 R⊙, nickel mass M(56Ni$)\, \sim 0.06\, \rm M_\odot$, pre-supernova mass 25 M⊙, mass of ejected envelope 23.6 M⊙, explosion energy E ∼ 2 × 1051 erg. The model progenitor mass M = 25 M⊙ significantly exceeds the upper limit mass M = 17 M⊙, obtained from analysis the pre-SNe observations. This result confirms once more that the ’Red Supergiant Problem’ must be resolved by stellar evolution and supernova explosion theories in interaction with observations.

Mass discrepancy analysis for a select sample of Type II-Plateau supernovae

The detailed study of supernovae (SNe) and their progenitors allows a better understanding of the evolution of massive stars and how these end their lives. Despite its importance, the range of physical parameters for the most common type of explosion, the type II supernovae (SNe II), is still unknown. In particular, previous studies of type II-Plateau supernovae (SNe II-P) showed a discrepancy between the progenitor masses inferred from hydrodynamic models and those determined from the analysis of direct detections in archival images. Our goal is to derive physical parameters (progenitor mass, radius, explosion energy and total mass of nickel) through hydrodynamical modelling of light curves and expansion velocity evolution for a select group of six SNe II-P (SN 2004A, SN 2004et, SN 2005cs, SN 2008bk, SN 2012aw, and SN 2012ec) that fulfilled the following three criteria: (1) enough photometric and spectroscopic monitoring is available to allow for a reliable hydrodynamical modelling; (2) a direct progenitor detection has been achieved; and (3) there exists confirmation of the progenitor identification via its disappearance in post-explosion images. We then compare the masses obtained by our hydrodynamic models with those obtained by direct detections of the progenitors to test the existence of such a discrepancy. As opposed to some previous works, we find good agreement between both methods. We obtain a wide range in the physical parameters for our SN sample. We infer presupernova masses between 10 and 23 M⊙, progenitor radii between 400 and 1250 R⊙, explosion energies between 0.2 and 1.4 foe, and 56Ni masses between 0.0015 and 0.085 M⊙. An analysis of possible correlations between different explosion parameters is presented. The clearest relation found is that between the mass and the explosion energy, in the sense that more-massive objects produce higher-energy explosions, in agreement with previous studies. Finally, we also compare our results with previous physical–observed parameter relations widely used in the literature. We find significant differences between both methods, which indicates that caution should be exercised when using these relations.

The disappearance of the progenitor of SN 2012aw in late-time imaging

Abstract We present new late-time near-infrared imaging of the site of the nearby core-collapse supernova SN 2012aw, confirming the disappearance of the point source identified by Fraser et al. and Van Dyk et al. as a candidate progenitor in both J and Ks filters. We remeasure the progenitor photometry, and find that both the J and Ks magnitudes of the source are consistent with those quoted in the literature. We also recover a marginal detection of the progenitor in H-band, for which we measure H = 19.67 ± 0.40 mag. Comparing the luminosity of the progenitor to stellar evolutionary models, SN 2012aw appears to have resulted from the explosion of a 12.5 ± 1.5 M⊙ red supergiant.

Revisiting the red supergiant progenitors of core-collapse supernovae

AbstractI will present a reanalysis of the properties of the red supergiant (RSG) progenitors of several extragalactic core-collapse, Type II-Plateau supernovae, including SN 2012aw, SN 2013ej, SN 2004et, and SN 2008bk. The observed spectral energy distributions (SEDs) for these stars, from the optical to the infrared, are compared with model SEDs for Galactic RSGs, as well as with the observed SEDs of analogous RSGs in Local Group galaxies. As a result, new estimates of the stellar temperatures and luminosities for the progenitors are obtained, and through comparison with recent massive stellar evolutionary tracks, new inferences are made for the progenitors initial masses. I will place these in the context of the RSG SN progenitor mass spectrum and of the so-called “red supergiant problem.”

SN 2013ej: A TYPE IIL SUPERNOVA WITH WEAK SIGNS OF INTERACTION

We present optical photometric and spectroscopic observations of SN 2013ej. It is one of the brightest Type II supernovae (SNe II) exploded in a nearby (∼10 Mpc) galaxy, NGC 628. The light-curve characteristics are similar to SNe II, but with a relatively shorter (∼85 days) and steeper (∼1.7 mag (100 days)−1 in V) plateau phase. The SN shows a large drop of 2.4 mag in V-band brightness during the plateau-to-nebular transition. The absolute ultraviolet (UV) light curves are identical to SN 2012aw, showing a similar UV-plateau trend extending up to 85 days. The radioactive 56Ni mass estimated from the tail luminosity is 0.02 , which is significantly lower than typical SNe IIP. The characteristics of spectral features and evolution of line velocities indicate that SN 2013ej is a Type II event. However, light-curve characteristics and some spectroscopic features provide strong support in classifying it as a Type IIL event. A detailed synow modeling of spectra indicates the presence of some high-velocity components in Hα and Hβ profiles, implying a possible ejecta–circumstellar medium interaction. The nebular phase spectrum shows an unusual notch in the Hα emission, which may indicate bipolar distribution of 56Ni. Modeling of the bolometric light curve yields a progenitor mass of ∼14 and a radius of ∼450 , with a total explosion energy of erg.

Broad-band polarimetric follow-up of Type IIP SN 2012aw

We present the results based on R-band polarimetric follow-up observations of the nearby (~10 Mpc) Type II-plateau SN 2012aw. Starting from ~10 days after the SN explosion, these polarimetric observations cover ~90 days (during the plateau phase) and are distributed over 9 epochs. To characterize the Milky Way interstellar polarization (ISP_MW ), we have observed 14 field stars lying in a radius of 10 degree around the SN. We have also tried to subtract the host galaxy dust polarization component assuming that the dust properties in the host galaxy are similar to that observed for Galactic dust and the general magnetic field follow the large scale structure of the spiral arms of a galaxy. After correcting the IS_PMW , our analysis infer that SN 2012aw has maximum polarization of 0.85% +- 0.08% but polarization angle does not show much variation with a weighted mean value of ~138 degree. However, if both ISP_MW and host galaxy polarization (ISP_HG ) components are subtracted from the observed polarization values of SN, maximum polarization of the SN becomes 0.68% +- 0.08%. The distribution of Q and U parameters appears to follow a loop like structure. The evolution of polarimetric light curve (PLC) properties of this event is also compared with other well studied core-collapse supernovae of similar type.

THE TYPE IIP SUPERNOVA 2012aw IN M95: HYDRODYNAMICAL MODELING OF THE PHOTOSPHERIC PHASE FROM ACCURATE SPECTROPHOTOMETRIC MONITORING

We present an extensive optical and near-infrared photometric and spectroscopic campaign of the type IIP supernova SN 2012aw. The dataset densely covers the evolution of SN 2012aw shortly after the explosion up to the end of the photospheric phase, with two additional photometric observations collected during the nebular phase, to fit the radioactive tail and estimate the $^{56}$Ni mass. Also included in our analysis is the already published \textit{Swift} UV data, therefore providing a complete view of the ultraviolet-optical-infrared evolution of the photospheric phase. On the basis of our dataset, we estimate all the relevant physical parameters of SN 2012aw with our radiation-hydrodynamics code: envelope mass $M_{env} \sim 20 M_\odot$, progenitor radius $R \sim 3 \times 10^{13}$ cm ($ \sim 430 R_\odot$), explosion energy $E \sim 1.5$ foe, and initial $^{56}$Ni mass $\sim 0.06$ $M_\odot$. These mass and radius values are reasonably well supported by independent evolutionary models of the progenitor, and may suggest a progenitor mass higher than the observational limit of $16.5 \pm 1.5 M_\odot$ of the Type IIP events.

The nebular spectra of SN 2012aw and constraints on stellar nucleosynthesis from oxygen emission lines

We present nebular phase optical and near-infrared spectroscopy of the Type IIP supernova SN 2012aw combined with NLTE radiative transfer calculations applied to ejecta from stellar evolution/explosion models. Our spectral synthesis models generally show good agreement with the ejecta from a MZAMS = 15 Msun progenitor star. The emission lines of oxygen, sodium, and magnesium are all consistent with the nucleosynthesis in a progenitor in the 14 - 18 Msun range. We also demonstrate how the evolution of the oxygen cooling lines of [O I] 5577 A, [O I] 6300 A, and [O I] 6364 A can be used to constrain the mass of oxygen in the non-molecularly cooled ashes to < 1 Msun, independent of the mixing in the ejecta. This constraint implies that any progenitor model of initial mass greater than 20 Msun would be difficult to reconcile with the observed line strengths. A stellar progenitor of around MZAMS = 15 Msun can consistently explain the directly measured luminosity of the progenitor star, the observed nebular spectra, and the inferred pre-supernova mass-loss rate. We conclude that there is still no convincing example of a Type IIP explosion showing the nucleosynthesis expected from a MZAMS > 20 Msun progenitor.

Supernova 2012aw – a high-energy clone of archetypal Type IIP SN 1999em

We present densely-sampled UBVRI/griz photometric and low-resolution (6-10A) optical spectroscopic observations from 4 to 270 days after explosion of a newly discovered type II SN 2012aw in a nearby (~9.9 Mpc) galaxy M95. The light-curve characteristics of apparent magnitudes, colors, bolometric luminosity and the presence and evolution of prominent spectral features are found to have striking similarity with the archetypal IIP SNe 1999em, 1999gi and 2004et. The early time observations of SN 2012aw clearly detect minima in the light-curve of V, R and I bands near 37 days after explosion and this we suggest to be an observational evidence for emergence of recombination phase. The mid-plateau MV magnitude (-16.67 $\pm$ 0.04) lies in between the bright (~ -18) and subluminous (~ -15) IIP SNe. The mass of nickel is 0.06$\pm$0.01 M_sun. The SYNOW modelling of spectra indicate that the value and evolution of photospheric velocity is similar to SN 2004et, but about ~600 km/s higher than that of SNe 1999em and 1999gi at comparable epochs. This trend is more apparent in the line velocities of H alpha and H beta. A comparison of ejecta velocity properties with that of existing radiation-hydrodynamical simulations indicate that the energy of explosion lies in the range 1-2x10^51 ergs; a further comparison of nebular phase [Oi] doublet luminosity with SNe 2004et and 1987A indicate that the mass of progenitor star is about 14-15 M_sun. The presence of high-velocity absorption features in the mid-to-late plateau and possibly in early phase spectra show signs of interaction between ejecta and the circumstellar matter; being consistent with its early-time detection at X-ray and radio wavebands.

Optical observations of supernova 2012aw

AbstractWe present optical UBVRI photometric and low-resolution spectroscopic follow-up observations of a type II SN 2012aw in a nearby (~10 Mpc) galaxy M95 during 4 to 270 days post-explosion. The evolution characteristics of optical brightness and color are found to have striking similarity with the archetypal type IIP SN 1999em. The mid-plateau MV is −16.7 mag and the ejected nickel mass is ~0.06 M⊙. The presence and evolution of optical spectral features during 7d to 104d are also similar to SN 1999em as well as other normal type IIP events. The mid-plateau photospheric velocity is around 4200 km s−1 which is same as that of SN 2004et at similar phases, indicating similar energy of explosion i.e. 2 × 1051 erg s−1.

RED AND DEAD: THE PROGENITOR OF SN 2012aw IN M95

Core-collapse supernovae (SNe) are the spectacular finale to massive stellar evolution. In this Letter, we identify a progenitor for the nearby core-collapse SN 2012aw in both ground based near-infrared, and space based optical pre-explosion imaging. The SN itself appears to be a normal Type II Plateau event, reaching a bolometric luminosity of 10$^{42}$ erg s$^{-1}$ and photospheric velocities of $\sim$11,000 \kms\ from the position of the H$\beta$ P-Cygni minimum in the early SN spectra. We use an adaptive optics image to show that the SN is coincident to within 27 mas with a faint, red source in pre-explosion HST+WFPC2, VLT+ISAAC and NTT+SOFI images. The source has magnitudes $F555W$=26.70$\pm$0.06, $F814W$=23.39$\pm$0.02, $J$=21.1$\pm$0.2, $K$=19.1$\pm$0.4, which when compared to a grid of stellar models best matches a red supergiant. Interestingly, the spectral energy distribution of the progenitor also implies an extinction of $A_V>$1.2 mag, whereas the SN itself does not appear to be significantly extinguished. We interpret this as evidence for the destruction of dust in the SN explosion. The progenitor candidate has a luminosity between 5.0 and 5.6 log L/\lsun, corresponding to a ZAMS mass between 14 and 26 \msun\ (depending on $A_V$), which would make this one of the most massive progenitors found for a core-collapse SN to date.

ON ABSORPTION BY CIRCUMSTELLAR DUST, WITH THE PROGENITOR OF SN 2012aw AS A CASE STUDY

ABSTRACT We use the progenitor of SN 2012aw to illustrate the consequences of modeling circumstellar dust using Galactic (interstellar) extinction laws that (1) ignore dust emission in the near-IR and beyond, (2) average over dust compositions, and (3) mischaracterize the optical/UV absorption by assuming that scattered photons are lost to the observer. The primary consequences for the progenitor of SN 2012aw are that both the luminosity and the absorption are significantly overestimated. In particular, the stellar luminosity is most likely in the range 104.8 &lt; L */L ☉ &lt; 105.0 and the star was not extremely massive for a Type IIP progenitor, with M * &lt; 15 M ☉. Given the properties of the circumstellar dust and the early X-ray/radio detections of SN 2012aw, the star was probably obscured by an ongoing wind with to 10−5.0 M ☉ yr−1 at the time of the explosion, roughly consistent with the expected mass-loss rates for a star of its temperature (T * ≃ 3600+300 − 200 K) and luminosity. In the spirit of Galactic extinction laws, we supply simple interpolation formulae for circumstellar extinction by dusty graphitic and silicate shells as a function of wavelength (λ ⩾ 0.3 μm) and total (absorption plus scattering) V-band optical depth (τ V ⩽ 20). These do not include the contributions of dust emission, but provide a simple, physical alternative to incorrectly using interstellar extinction laws.

BVRI lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95, and SN 2012cg in NGC 4424

Accurate and densely populated BVRCIC lightcurves of supernovae SN 2011fe in M101, SN 2012aw in M95 and SN 2012cg in NGC 4424 are presented and discussed. The SN 2011fe lightcurves span a total range of 342days, from 17days pre- to 325days post-maximum. The observations of both SN 2012aw and SN 2012cg were stopped by solar conjunction, when the objects were still bright. The lightcurve for SN 2012aw covers 92days, that of SN 2012cg spans 44days. Time and brightness of maxima are measured, and from the lightcurve shapes and decline rates the absolute magnitudes are obtained, and the derived distances are compared to that of the parent galaxies. The color evolution and the bolometric lightcurves are evaluated in comparison with those of other well observed supernovae, showing no significant deviations.