arXiv subjects

Mattias Ergon

Publications and source records attributed to Mattias Ergon.

12 recordsLinked to original sources

arXiv2025

Hydrodynamical modelling of Type IIb SNe

We present HYDE, a new one-dimensional hydrodynamical code, and use it to construct a grid of supernova (SN) models based on solar-metallicity bare helium-core models evolved to the verge of core-collapse with MESA STAR. This grid is suited to model Type IIb SNe, which progenitor stars are thought to have lost all but a tiny fraction of their hydrogen envelopes. Using an automated procedure we fit the bolometric lightcurves and photospheric velocities for a large sample of (17) Type IIb SNe to the grid of SN models. We find that the distribution of initial masses for the sample can be reasonably well described by a standard Salpeter IMF, although there is an under-population in the >25 M$_\odot$ range. The fractions of SNe with initial masses <15 M$_\odot$ and <20 M$_\odot$ are 56 and 81 percent, respectively, suggesting either the binary channel to dominate the production of Type IIb SNe or a flaw in our understanding of single-star mass-loss. We find correlations between the explosion energy, initial mass and mass of $^{56}$Ni; the explosion energy increases with initial mass and the mass of $^{56}$Ni increases with explosion energy. The method used allows us to determine the errors in the model parameters arising from the observed quantities and the degeneracy of the solution. We find that an error in the distance and extinction propagates mainly to the derived mass of $^{56}$Ni, whereas an error in the photospheric velocity propagates mainly to the derived helium-core mass and explosion energy. Fits using the bolometric lightcurve alone are completely degenerate along the M$_{\mathrm{ej}}^{2}$/E$_{\mathrm{ej}}$=const curve, whereas fits using also the photospheric velocities are quite robust for well-sampled SNe. Finally, we provide a description and tests of the HYDE code, and a discussion of the limitations of the method used.

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arXiv2023

Lightcurve and spectral modelling of the Type IIb SN 2020acat. Evidence for a strong Ni bubble effect on the diffusion time

We use the light curve and spectral synthesis code JEKYLL to calculate a set of macroscopically mixed Type IIb supernova (SN) models, which are compared to both previously published and new late-phase observations of SN 2020acat. The models differ in the initial mass, the radial mixing and expansion of the radioactive material, and the properties of the hydrogen envelope. The best match to the photospheric and nebular spectra and lightcurves of SN 2020acat is found for a model with an initial mass of 17 solar masses, strong radial mixing and expansion of the radioactive material, and a 0.1 solar mass hydrogen envelope with a low hydrogen mass-fraction of 0.27. The most interesting result is that strong expansion of the clumps containing radioactive material seems to be required to fit the observations of SN 2020acat both in the diffusion phase and the nebular phase. These "Ni bubbles" are expected to expand due to heating from radioactive decays, but the degree of expansion is poorly constrained. Without strong expansion there is a tension between the diffusion phase and the subsequent evolution, and models that fit the nebular phase produce a diffusion peak that is too broad. The diffusion phase lightcurve is sensitive to the expansion of the "Ni bubbles", as the resulting Swiss-cheese-like geometry decreases the effective opacity and therefore the diffusion time. This effect has not been taken into account in previous lightcurve modelling of stripped-envelope SNe, which may lead to a systematic underestimate of their ejecta masses. It should be emphasized, though, that JEKYLL is limited to a geometry that is spherically symmetric on average, and large-scale asymmetries may also play a role. The relatively high initial mass found for the progenitor of SN 2020acat places it at the upper end of the mass distribution of Type IIb SN progenitors, and a single star origin can not be excluded.

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arXiv2022

Spectral modelling of Type IIb Supernovae

We use the new NLTE lightcurve and spectral synthesis code JEKYLL to evolve a macroscopically mixed ejecta model of a type IIb Supernova (SN) originating from a star with an initial mass of 12 solar masses through the photospheric and nebular phase. We compare to SN 2011dh, and find that both the spectra and the lightcurves are well reproduced. Our work further strengthens the evidence that this SN originated from a star with an initial mass of about 12 solar masses that had lost all but tiny (<0.1 solar masses) fraction of its hydrogen envelope. We also investigate the effects of the macroscopic mixing by comparing macroscopically and microscopically mixed models, and by varying the clumping geometry. In the photospheric phase, we find strong effects on the effective opacity in the macroscopically mixed regions, which affects the model lightcurves. The diffusion peak is considerably narrower in the macroscopically mixed case, and differs strongly if the radioactive material in the helium envelope is allowed to expand more than in our standard model. The effect is mainly geometrical, and is driven by the expansion of the clumps containing radioactive material. These findings has implications for lightcurve modelling of stripped-envelope SNe in general, and the effect would increase the estimated ejecta masses. In the nebular phase, we find strong effects on the collisional cooling rates in the macroscopically mixed regions, which affects lines driven by collisional cooling, in particular the [Ca II] 7291, 7323 and [O I] 6300, 6364 lines. As these lines are often used for mass determinations, it highlights the importance of how the calcium- and oxygen-rich material is mixed. As shown in this and earlier work, both NLTE and macroscopic mixing are essential ingredients to accurately model the lightcurves and spectra of Type IIb SNe throughout their evolution.

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arXiv2020

A non-equipartition shockwave traveling in a dense circumstellar environment around SN2020oi

We report the discovery and panchromatic followup observations of the young Type Ic supernova, SN2020oi, in M100, a grand design spiral galaxy at a mere distance of $14$ Mpc. We followed up with observations at radio, X-ray and optical wavelengths from only a few days to several months after explosion. The optical behaviour of the supernova is similar to those of other normal Type Ic supernovae. The event was not detected in the X-ray band but our radio observation revealed a bright mJy source ($L_ν \approx 1.2 \times 10^{27} {\rm erg\,s}^{-1} {\rm Hz}^{-1}$). Given, the relatively small number of stripped envelope SNe for which radio emission is detectable, we used this opportunity to perform a detailed analysis of the comprehensive radio dataset we obtained. The radio emitting electrons initially experience a phase of inverse Compton cooling which leads to steepening of the spectral index of the radio emission. Our analysis of the cooling frequency points to a large deviation from equipartition at the level of $ε_e/ε_B \gtrsim 200$, similar to a few other cases of stripped envelope SNe. Our modeling of the radio data suggests that the shockwave driven by the SN ejecta into the circumstellar matter (CSM) is moving at $\sim 3\times 10^{4}\,{\rm km\,s}^{-1}$. Assuming a constant mass-loss from the stellar progenitor, we find that the mass-loss rate is $\dot{M} \approx 1.4\times 10^{-4}\,{M}_{\odot}\,{\rm yr}^{-1}$, for an assumed wind velocity of $1000\,{\rm km\,s}^{-1}$. The temporal evolution of the radio emission suggests a radial CSM density structure steeper than the standard $r^{-2}$.

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arXiv2019

Evidence for Late-stage Eruptive Mass-loss in the Progenitor to SN2018gep, a Broad-lined Ic Supernova: Pre-explosion Emission and a Rapidly Rising Luminous Transient

We present detailed observations of ZTF18abukavn (SN2018gep), discovered in high-cadence data from the Zwicky Transient Facility as a rapidly rising ($1.4\pm0.1$ mag/hr) and luminous ($M_{g,\mathrm{peak}}=-20$ mag) transient. It is spectroscopically classified as a broad-lined stripped-envelope supernova (Ic-BL SN). The high peak luminosity ($L_{\mathrm{bol}} \gtrsim 3 \times 10^{44}$ erg $\mathrm{sec}^{-1}$), the short rise time ($t_{\mathrm{rise}}= 3$ days in $g$-band), and the blue colors at peak ($g-r\sim-0.4$) all resemble the high-redshift Ic-BL iPTF16asu, as well as several other unclassified fast transients. The early discovery of SN2018gep (within an hour of shock breakout) enabled an intensive spectroscopic campaign, including the highest-temperature ($T_{\mathrm{eff}}\gtrsim40,000$ K) spectra of a stripped-envelope SN. A retrospective search revealed luminous ($M_g \sim M_r \approx -14\,$mag) emission in the days to weeks before explosion, the first definitive detection of precursor emission for a Ic-BL. We find a limit on the isotropic gamma-ray energy release $E_\mathrm{γ,iso}<4.9 \times 10^{48}$ erg, a limit on X-ray emission $L_{\mathrm{X}} < 10^{40}\,$erg sec$^{-1}$, and a limit on radio emission $νL_ν\lesssim 10^{37}\,$erg sec$^{-1}$. Taken together, we find that the early ($<10\,$days) data are best explained by shock breakout in a massive shell of dense circumstellar material ($0.02\,M_\odot$) at large radii ($3 \times 10^{14}\,$cm) that was ejected in eruptive pre-explosion mass-loss episodes. The late-time ($>10$ days) light curve requires an additional energy source, which could be the radioactive decay of Ni-56.

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arXiv2019

Evolution of the progenitors of SNe 1993J and 2011dh revealed through late time radio and X-ray studies

We perform hydrodynamical simulations of the interaction between supernova (SN) ejecta and circumstellar medium (CSM) for SN 1993J and SN 2011dh, and calculate the radio and X-ray emissions expected from the shocked gas at late epochs ($t$). Considering the ejecta structure from multi-group radiation hydrodynamics simulation, we find that the observed rapid drop in radio and X-ray light curves of SN 1993J at $t>$3000 days can be due to a change in the mass-loss rate ($\dot M$) around $\sim$6500 years prior to the explosion of the SN. The exact epoch scales inversely with the assumed wind velocity of $v_{\rm w}=10~ km~s^{-1}$. The progenitor of this SN very likely belonged to a binary system, where, during its evolution, the primary had transferred material to the secondary. It is argued in the paper that the change in $\dot M$ can happen because of a change in the mass accretion efficiency ($η$) of the companion star. It is possible that before $\sim6500~(v_{\rm w}/10~km~s^{-1})^{-1}$years prior to the explosion, $η$ was high, thus the CSM was tenuous, which causes the late time downturn in fluxes. In the case of SN 2011dh, the late time evolution is found to be consistent with a wind medium with $\dot M/v_{\rm w}=4\times10^{-6 }~M_{\odot}~ yr^{-1}/10 ~{km ~s^{-1}}$. It is difficult from our analysis to predict whether the progenitor of this SN had a binary companion, however, if future observations show similar decrease in radio and X-ray fluxes, then that would give strong support to a scenario where both SNe had undergone similar kind of binary evolution before explosion.

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arXiv2015

On the nature of rapidly fading Type II supernovae

It has been suggested that Type II supernovae with rapidly fading light curves (a.k.a. Type IIL supernovae) are explosions of progenitors with low-mass hydrogen-rich envelopes which are of the order of 1 Msun. We investigate light-curve properties of supernovae from such progenitors. We confirm that such progenitors lead to rapidly fading Type II supernovae. We find that the luminosity of supernovae from such progenitors with the canonical explosion energy of 1e51 erg and 56Ni mass of 0.05 Msun can increase temporarily shortly before all the hydrogen in the envelope recombines. As a result, a bump appears in their light curves. The bump appears because the heating from the nuclear decay of 56Ni can keep the bottom of hydrogen-rich layers in the ejecta ionized, and thus the photosphere can stay there for a while. We find that the light-curve bump becomes less significant when we make explosion energy larger (>~ 2e51 erg), 56Ni mass smaller (<~ 0.01 Msun), 56Ni mixed in the ejecta, or the progenitor radius larger. Helium mixing in hydrogen-rich layers makes the light-curve decline rates large but does not help reducing the light-curve bump. Because the light-curve bump we found in our light-curve models has not been observed in rapidly fading Type II supernovae, they may be characterized by not only low-mass hydrogen-rich envelopes but also higher explosion energy, larger degrees of 56Ni mixing, and/or larger progenitor radii than slowly fading Type II supernovae, so that the light-curve bump does not become significant.

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arXiv2014

High Density Circumstellar Interaction in the Luminous Type IIn SN 2010jl: The first 1100 days

HST and ground based observations of the Type IIn SN 2010jl are analyzed, including photometry, spectroscopy in the ultraviolet, optical and NIR bands, 26-1128 days after first detection. At maximum the bolometric luminosity was $\sim 3\times10^{43}$ erg/s and even at 850 days exceeds $10^{42}$ erg/s. A NIR excess, dominating after 400 days, probably originates in dust in the circumstellar medium (CSM). The total radiated energy is $> 6.5\times10^{50}$ ergs, excluding the dust component. The spectral lines can be separated into one broad component due to electron scattering, and one narrow with expansion velocity $\sim 100$ km/s from the CSM. The broad component is initially symmetric around zero velocity but becomes blueshifted after $\sim 50$ days, while remaining symmetric about a shifted centroid velocity. Dust absorption in the ejecta is unlikely to explain the line shifts, and we attribute the shift instead to acceleration by the SN radiation. From the optical lines and the X-ray and dust properties, there is strong evidence for large scale asymmetries in the CSM. The ultraviolet lines indicate CNO processing in the progenitor, while the optical shows a number of narrow coronal lines excited by the X-rays. The bolometric light curve is consistent with a radiative shock in an $r^{-2}$ CSM with a mass loss rate of $\sim 0.1$ M_sun/yr. The total mass lost is $> 3$ M_sun. These properties are consistent with the SN expanding into a CSM characteristic of an LBV progenitor with a bipolar geometry. The apparent absence of nuclear processing is attributed to a CSM still opaque to electron scattering.

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arXiv2013

The Disappearance of the Red Supergiant Progenitor of Supernova 2008bk

Massive stars end their lives in spectacular supernova explosions. Identifying the progenitor star is a test of stellar evolution and explosion models. Here we show that the progenitor star of the supernova SN 2008bk has now disappeared, which provides conclusive evidence that this was the death of a red supergiant star.

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arXiv2012

The progenitor mass of the Type IIP supernova SN 2004et from late-time spectral modeling

SN 2004et is one of the nearest and best-observed Type IIP supernovae, with a progenitor detection as well as good photometric and spectroscopic observational coverage well into the nebular phase. Based on nucleosynthesis from stellar evolution/explosion models we apply spectral modeling to analyze its 140-700 day evolution from ultraviolet to mid-infrared. We find a M_ZAMS= 15 Msun progenitor star (with an oxygen mass of 0.8 Msun) to satisfactorily reproduce [O I] 6300, 6364 Å and other emission lines of carbon, sodium, magnesium, and silicon, while 12 Msun and 19 Msun models under- and overproduce most of these lines, respectively. This result is in fair agreement with the mass derived from the progenitor detection, but in disagreement with hydrodynamical modeling of the early-time light curve. From modeling of the mid-infrared iron-group emission lines, we determine the density of the "Ni-bubble" to rho(t) = 7E-14*(t/100d)^-3 g cm^-3, corresponding to a filling factor of f = 0.15 in the metal core region (V = 1800 km/s). We also confirm that silicate dust, CO, and SiO emission are all present in the spectra.

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arXiv2012

The Type IIb Supernova 2011dh from a Supergiant Progenitor

A set of hydrodynamical models based on stellar evolutionary progenitors is used to study the nature of SN 2011dh. Our modeling suggests that a large progenitor star ---with R ~200 Rsun---, is needed to reproduce the early light curve of SN 2011dh. This is consistent with the suggestion that the yellow super-giant star detected at the location of the SN in deep pre-explosion images is the progenitor star. From the main peak of the bolometric light curve and expansion velocities we constrain the mass of the ejecta to be ~2 Msun, the explosion energy to be E= 6-10 x 10^50 erg, and the 56Ni mass to be approximately 0.06 Msun. The progenitor star was composed of a helium core of 3 to 4 Msun and a thin hydrogen-rich envelope of ~0.1 M_sun with a main sequence mass estimated to be in the range of 12--15 Msun. Our models rule out progenitors with helium-core masses larger than 8 Msun, which correspond to M_ZAMS > 25 Msun. This suggests that a single star evolutionary scenario for SN 2011dh is unlikely.

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arXiv2012

A spectroscopically normal type Ic supernova from a very massive progenitor

We present observations of the Type Ic supernova (SN Ic) 2011bm spanning a period of about one year. The data establish that SN 2011bm is a spectroscopically normal SN Ic with moderately low ejecta velocities and with a very slow spectroscopic and photometric evolution (more than twice as slow as SN 1998bw). The Pan-STARRS1 retrospective detection shows that the rise time from explosion to peak was 40 days in the R band. Through an analysis of the light curve and the spectral sequence, we estimate a kinetic energy of 7-17 foe and a total ejected mass of 7-17 Mo, 5-10 Mo of which is oxygen and 0.6-0.7 Mo is 56Ni. The physical parameters obtained for SN 2011bm suggest that its progenitor was a massive star of initial mass 30-50 Mo. The profile of the forbidden oxygen lines in the nebular spectra show no evidence of a bi-polar geometry in the ejected material.

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