SN 1999em Research Articles

HOLISMOKES

We investigate strongly gravitationally lensed type II supernovae (LSNe II) for time-delay cosmography, incorporating microlensing effects; this expands on previous microlensing studies of type Ia supernovae (SNe Ia). We use the radiative-transfer code TARDIS to recreate five spectra of the prototypical SN 1999em at different times within the plateau phase of the light curve. The microlensing-induced deformations of the spectra and light curves are calculated by placing the SN into magnification maps generated with the code GERLUMPH. We study the impact of microlensing on the color curves and find that there is no strong influence on them during the investigated time interval of the plateau phase. The color curves are only weakly affected by microlensing due to the almost achromatic behavior of the intensity profiles. However, the lack of nonlinear structure in the color curves during the plateau phase of type II-plateau supernovae makes time-delay measurements more challenging compared to SN Ia color curves, given the possible presence of differential dust extinction. Therefore, we further investigate SN phase inference through spectral absorption lines under the influence of microlensing and Gaussian noise. As the spectral features shift to longer wavelengths with progressing time after explosion, the measured wavelength of a specific absorption line provides information on the epoch of the SN. The comparison between retrieved epochs of two observed lensing images then gives the time delay of the images. We find that the phase retrieval method that uses spectral features yields accurate delays with uncertainties of ≲2 days, making it a promising approach.

Hydrodynamical Modeling of the Light Curves of Core-collapse Supernovae with HYPERION. I. The Mass Range 13–25 M⊙, the Metallicities −3 ≤ [Fe/H] ≤ 0, and the Case of SN 1999em

Abstract We present the last version of HYdrodynamic Ppm Explosion with Radiation diffusION (Hyperion), a hydrodynamic code designed to calculate the explosive nucleosynthesis, remnant mass, and light curve associated with the explosion of a massive star. By means of this code, we compute the explosion of a subset of red supergiant models taken from the database published by Limongi & Chieffi for various explosion energies in the range ∼0.20–2.00 × 1051 erg. The main outcomes of these simulations, i.e., remnant mass, synthesized 56Ni, luminosity, and length of the plateau of the bolometric light curve, are analyzed as a function of the initial parameters of the star (mass and metallicity) and the explosion energy. As a first application of Hyperion, we estimated the mass and metallicity of the progenitor star of SN 1999em, a well-studied Type IIP supernova, by means of the light-curve fitting. In particular, if the adopted distance to the host galaxy NGC 1637 is 7.83 Mpc, the properties of the light curve point toward a progenitor with an initial mass of 13 M ⊙ and a metallicity [Fe/H] = −1. If, on the contrary, the adopted distance modulus is 11.7 Mpc, all models with initial mass 13 ≤ M/M ⊙ ≤ 15 and metallicities −1 ≤ [Fe/H] ≤ 0 are compatible with the progenitor of SN 1999em.

A progenitor candidate for the type II-P supernova SN 2018aoq in NGC 4151

We present our findings based on pre- and post-explosion data of the type II-Plateau SN 2018aoq that exploded in NGC 4151. As distance estimates to NGC 4151 vary by an order of magnitude, we utilised the well-known correlation between ejecta velocity and plateau brightness, i.e. the standard candle method, to obtain a distance of 18.2 ± 1.2 Mpc, which is in very good agreement with measurements based on geometric methods. The above distance implies a mid-plateau absolute magnitude of MV50 = − 15.76 ± 0.14 suggesting that it is of intermediate brightness when compared to IIP SNe such as SN 2005cs at the faint end, and more typical events such as SN 1999em. This is further supported by relatively low expansion velocities (Fe IIλ5169 ∼ 3000 km s−1 at +42 d). Using archival HST/WFC3 imaging data, we find a point source coincident with the supernova position in the F350LP, F555W, F814W, and F160W filters. This source shows no significant variability over the ∼2 month time span of the data. From fits to the spectral energy distribution of the candidate progenitor, we find log(L/L⊙) ∼ 4.7 and Teff ∼ 3.5 kK, implying an M-type red supergiant progenitor. From comparisons to single and binary star models, we find that both favour the explosion of a star with a zero-age main sequence mass of ∼10 M⊙.

Light-curve Analysis of Ordinary Type IIP Supernovae Based on Neutrino-driven Explosion Simulations in Three Dimensions

Abstract Type II-plateau supernovae (SNe IIP) are the most numerous subclass of core-collapse SNe originating from massive stars. In the framework of the neutrino-driven explosion mechanism, we study the properties of the SN outburst for a red supergiant progenitor model and compare the corresponding light curves with observations of the ordinary Type IIP SN 1999em. Three-dimensional (3D) simulations of (parametrically triggered) neutrino-driven explosions are performed with the (explicit, finite-volume, Eulerian, multifluid hydrodynamics) code Prometheus, using a presupernova model of a 15 M ⊙ star as initial data. On approaching homologous expansion, the hydrodynamic and composition variables of the 3D models are mapped to a spherically symmetric configuration, and the simulations are continued with the (implicit, Lagrangian, radiation hydrodynamics) code Crab to follow the evolution of the blast wave during the SN outburst. Our 3D neutrino-driven explosion model with an explosion energy of about erg produces 56Ni in rough agreement with the amount deduced from fitting the radioactively powered light-curve tail of SN 1999em. The considered presupernova model, 3D explosion simulations, and light-curve calculations can explain the basic observational features of SN 1999em, except for those connected to the presupernova structure of the outer stellar layers. Our 3D simulations show that the distribution of 56Ni-rich matter in velocity space is asymmetric with a strong dipole component that is consistent with the observations of SN 1999em. The monotonic decline in luminosity from the plateau to the radioactive tail in ordinary SNe IIP is a manifestation of the intense turbulent mixing at the He/H composition interface.

SN 2013ej IN M74: A LUMINOUS AND FAST-DECLINING TYPE II-P SUPERNOVA

We present extensive ultraviolet, optical, and near-infrared observations of the Type IIP supernova (SN IIP) 2013ej in the nearby spiral galaxy M74. The multicolor light curves, spanning from similar to 8-185 days after explosion, show that it has a higher peak luminosity (i.e., M-V similar to -17.83 mag at maximum light), a faster post-peak decline, and a shorter plateau phase (i.e., similar to 50 days) compared to the normal Type IIP SN 1999em. The mass of Ni-56 is estimated as 0.02 +/- 0.01 M-circle dot from the radioactive tail of the bolometric light curve. The spectral evolution of SN 2013ej is similar to that of SN 2004et and SN 2007od, but shows a larger expansion velocity (i.e., v(Fe II) similar to 4600 km s(-1) at t similar to 50 days) and broader line profiles. In the nebular phase, the emission of the H alpha line displays a double-peak structure, perhaps due to the asymmetric distribution of Ni-56 produced in the explosion. With the constraints from the main observables such as bolometric light curve, expansion velocity, and photospheric temperature of SN 2013ej, we performed hydrodynamical simulations of the explosion parameters, yielding the. total explosion energy as similar to 0.7x 10(51) erg, the. radius of the progenitor as similar to 600 R-circle dot, and the ejected mass as similar to 10.6M(circle dot). These results suggest that SN 2013ej likely arose from a red supergiant with a mass of 12-13M(circle dot) immediately before the explosion.

Supernova 2012ec: identification of the progenitor and early monitoring with PESSTO

Abstract We present the identification of the progenitor of the Type IIP SN 2012ec in archival pre-explosion Hubble Space Telescope Wide Field Planetary Camera 2 (WFPC2) and Advanced Camera for Surveys Wide Field Channel F814W images. The properties of the progenitor are further constrained by non-detections in pre-explosion WFPC2 F450W and F606W images. We report a series of early photometric and spectroscopic observations of SN 2012ec. The r′-band light curve shows a plateau with $M_{r^{\prime }}=-17.0$. The early spectrum is similar to the Type IIP SN 1999em, with the expansion velocity measured at Hα absorption minimum of −11 700 km s−1 (at 1 d post-discovery). The photometric and spectroscopic evolution of SN 2012ec shows it to be a Type IIP SN, discovered only a few days post-explosion (<6 d). We derive a luminosity for the progenitor, in comparison with MARCS model spectral energy distributions, of $\log {L/\text{L}}_{\odot } = 5.15\pm 0.19$, from which we infer an initial mass range of 14–22 M⊙. This is the first SN with an identified progenitor to be followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO).

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.

Hydrogen recombination with multilevel atoms

Hydrogen recombination is one of the most important atomic processes in many astrophysical objects such as Type II supernova (SN~II) atmospheres, the high redshift universe during the cosmological recombination era, and H II regions in the interstellar medium. Accurate predictions of the ionization fraction can be quite different from those given by a simple solution if one takes into account many angular momentum sub-states, non-resonant processes, and calculates the rates of all atomic processes from the solution of the radiative transfer equation instead of using a Planck function under the assumption of thermal equilibrium. We use the general purpose model atmosphere code PHOENIX 1D to compare how the fundamental probabilities such as the photo-ionization probability, the escape probability, and the collisional de-excitation probability are affected by the presence of other metals in the environment, multiple angular momentum sub-states, and non-resonant processes. Our comparisons are based on a model of SN 1999em, a SNe Type II, 20 days after its explosion.

Optical and near-infrared coverage of SN 2004et: physical parameters and comparison with other Type IIP supernovae

We present new optical and near infrared (NIR) photometry and spectroscopy of the type IIP supernova, SN 2004et. In combination with already published data, this provides one of the most complete studies of optical and NIR data for any type IIP SN from just after explosion to +500 days. The contribution of the NIR flux to the bolometric light curve is estimated to increase from 15% at explosion to around 50% at the end of the plateau and then declines to 40% at 300 days. SN 2004et is one of the most luminous IIP SNe which has been well studied, and with a luminosity of log L = 42.3 erg/s, it is 2 times brighter than SN 1999em. We provide parametrised bolometric corrections as a function of time for SN 2004et and three other IIP SNe that have extensive optical and NIR data, which can be used as templates for future events. We compare the physical parameters of SN 2004et with those of other IIP SNe and find kinetic energies spanning the range of 10^50-10^51 ergs. We compare the ejected masses calculated from hydrodynamic models with the progenitor masses and limits derived from prediscovery images. Some of the ejected mass estimates are significantly higher than the progenitor mass estimates, with SN 2004et showing perhaps the most serious mass discrepancy. With current models, it appears difficult to reconcile 100 day plateau lengths and high expansion velocities with the low ejected masses of 5-6 Msun implied from 7-8 Msun progenitors. The nebular phase is studied using very late time HST photometry, along with optical and NIR spectroscopy. The light curve shows a clear flattening at 600 days in the optical and the NIR, which is likely due to the ejecta impacting on the CSM. We further show that the [Oi] 6300,6364 Angstrom line strengths of four type IIP SNe imply ejected oxygen masses of 0.5-1.5 Msun.

DO THE PHOTOMETRIC COLORS OF TYPE II-P SUPERNOVAE ALLOW ACCURATE DETERMINATION OF HOST GALAXY EXTINCTION?

We present infrared photometry of SN 1999em, plus optical photometry, infrared photometry, and optical spectroscopy of SN 2003hn. Both objects were Type II-P supernovae. The V-[RIJHK] color curves of these supernovae evolved in a very similar fashion until the end of plateau phase. This allows us to determine how much more extinction the light of SN 2003hn suffered compared to SN 1999em. Since we have an estimate of the total extinction suffered by SN 1999em from model fits of ground-based and space-based spectra as well as photometry of SN 1999em, we can estimate the total extinction and absolute magnitudes of SN 2003hn with reasonable accuracy. Since the host galaxy of SN 2003hn also produced the Type Ia SN 2001el, we can directly compare the absolute magnitudes of these two SNe of different types.

GALEX Spectroscopy of SN 2005ay Suggests Ultraviolet Spectral Uniformity among Type II-P Supernovae

We present the first results from our GALEX program designed to obtain ultraviolet (UV) spectroscopy of nearby core-collapse supernovae (SNe). Our first target, SN 2005ay in the nearby galaxy NGC 3938, is a typical member of the II-P SN subclass. Our spectra show remarkable similarity to those of the prototypical type II-P event SN 1999em, and resemble also Swift observations of the recent type II-P event SN 2005cs. Taken together, the observations of these three events trace the UV spectral evolution of SNe II-P during the first month after explosion, as required in order to interpret optical observations of high-redshift SNe II-P, and to derive cross-filter K-corrections. While still highly preliminary, the apparent UV homogeneity of SNe II-P bodes well for the use of these events as cosmological probes at high redshift.

Circumstellar Na I and Ca II lines in type IIP supernovae and SN 1998S

We investigate the possibility of detecting the circumstellar Na I D1,2 and Ca II H, K absorption lines in the spectra of type IIP supernovae at the photospheric phase. Our modeling shows that the Na I doublet lines will not be seen in the spectra of type IIP supernovae at moderate stellar wind densities, for example, characteristic of SN 1999em, while the rather intense Ca II lines with P Cyg profiles should be detectable. The same model is used to describe the circumstellar Na I and Ca II lines in the spectrum of SN 1998S, a type IIL supernova with a dense wind. We show that the circumstellar line intensities in this supernova are reproduced only if there is an ultraviolet excess that is mainly attributable to the Comptonization of supernova radiation in the shock wave.

Using Quantitative Spectroscopic Analysis to Determine the Properties and Distances of Type II Plateau Supernovae: SN 2005cs and SN 2006bp

We analyze the Type II plateau supernovae (SNe IIP) SN 2005cs and SN 2006bp with the non-LTE model atmosphere code CMFGEN. We fit 13 spectra in the first month for SN 2005cs and 18 for SN 2006bp. Swift ultraviolet photometry and ground-based optical photometry calibrate each spectrum. Our analysis shows that both objects were discovered less than 3 days after they exploded, making these the earliest SN IIP spectra ever studied. They reveal broad and very weak lines from highly ionized fast ejecta with an extremely steep density profile. We identify He II λ4686 emission in the SN 2006bp ejecta. Days later, the spectra resemble the prototypical Type IIP SN 1999em, which had a supergiant-like photospheric composition. Despite the association of SN 2005cs with possible X-ray emission, the emergent UV and optical light comes from the photosphere, not from circumstellar emission. We surmise that the very steep density falloff we infer at early times may be a fossil of the combined actions of the shock wave passage and radiation driving at shock breakout. Based on tailored CMFGEN models, the direct fitting technique and the expanding photosphere method both yield distances and explosion times that agree within a few percent. We derive a distance to NGC 5194, the host of SN 2005cs, of 8.9 ± 0.5 Mpc and 17.5 ± 0.8 Mpc for SN 2006bp in NGC 3953. The luminosity of SN 2006bp is 1.5 times that of SN 1999em and 6 times that of SN 2005cs. Reliable distances to SNe IIP that do not depend on a small range in luminosity provide an independent route to the Hubble constant and improved constraints on other cosmological parameters.

Time-dependent effects in photospheric-phase Type II supernova spectra

Spectroscopic modelling of Type II supernovae (SNe) generally assumes steady state. Following the recent suggestion of Utrobin & Chugai, but using the 1D non-local thermodynamic equilibrium line-blanketed model atmosphere code cmfgen, we investigate the effects of including time-dependent terms, which are generally neglected, that appear in the statistical and radiative equilibrium equations. We base our discussion on the ejecta properties and the spectroscopic signatures obtained from time-dependent simulations, investigating different ejecta configurations (slow, standard and fast), and covering their evolution from one day to six weeks after shock breakout. Compared to equivalent steady-state models, our time-dependent models produce SN ejecta that are systematically overionized, affecting helium at one week after explosion, but ultimately affecting all ions after a few weeks. While the continuum remains essentially unchanged, time-dependence effects on observed spectral lines are large. At the recombination epoch, H i lines and Na i D are considerably stronger and broader than in equivalent steady-state models, while Ca ii 8500 A is weakened. If time dependence is allowed for, the He i lines at 5875 and 10 830 A appear approximately three times stronger at one week, and He i 10 830 A persists as a blueshifted absorption feature even at six weeks after explosion. Time dependence operates through the energy gain from changes in ionization and excitation and, perhaps more universally across SN types, from the competition between recombination and expansion which, in turn, can be affected by optical depth effects. Our time-dependent models compare well with observations of the low-luminosity low-velocity SN 1999br and the more standard SN 1999em, reproducing the Hα line strength at the recombination epoch, and without the need for setting unphysical requirements on the magnitude of nickel mixing.

Optical Signatures of Circumstellar Interaction in Type IIP Supernovae

We propose new diagnostics for circumstellar interaction in Type IIP supernovae by the detection of high velocity (HV) absorption features in Halpha and He I 10830 A lines during the photospheric stage. To demonstrate the method, we compute the ionization and excitation of H and He in supernova ejecta taking into account time-dependent effects and X-ray irradiation. We find that the interaction with a typical red supergiant wind should result in the enhanced excitation of the outer layers of unshocked ejecta and the emergence of corresponding HV absorption, i.e. a depression in the blue absorption wing of Halpha and a pronounced absorption of He I 10830 A at a radial velocity of about -10,000 km/s. We identify HV absorption in Halpha and He I 10830 A lines of SN 1999em and in Halpha of SN 2004dj as being due to this effect. The derived mass loss rate is close to 10^{-6} Msun/yr for both supernovae, assuming a wind velocity 10 km/s. We argue that, in addition to the HV absorption formed in the unshocked ejecta, spectra of SN 2004dj and SN 1999em show a HV notch feature that is formed in the cool dense shell (CDS) modified by the Rayleigh-Taylor instability. The CDS results from both shock breakout and radiative cooling of gas that has passed through the reverse shock wave. The notch becomes dominant in the HV absorption during the late photospheric phase, ~60 d. The wind density deduced from the velocity of the CDS is consistent with the wind density found from the HV absorption produced by unshocked ejecta.

An optimal hydrodynamic model for the normal type IIP supernova 1999em

There is still no consensus about progenitor masses of Type IIP supernovae. We study a normal Type IIP SN 1999em in detail and compare it to a peculiar Type IIP SN 1987A. We computed the hydrodynamic and time-dependent atmosphere models interpreting simultaneously both the photometric and spectroscopic observations. The bolometric light curve of SN 1999em and the spectral evolution of its H-alpha line are consistent with a presupernova radius of 500 Rsun, an ejecta mass of 19.0 Msun, an explosion energy of 1.3x10^51 erg, and a radioactive 56Ni mass of 0.036 Msun. A mutual mixing of hydrogen-rich and helium-rich matter in the inner layers of the ejecta guarantees a good fit of the calculated light curve to that observed. Based on the hydrodynamic models in the vicinity of the optimal model, we derive the approximate relationships between the basic physical and observed parameters. We find that the hydrogen recombination in the atmosphere of a normal Type IIP SN 1999em, as well as most likely other Type IIP supernovae at the photospheric epoch, is essentially a time-dependent phenomenon. It is also shown that in normal Type IIP supernovae the homologous expansion of the ejecta in its atmosphere takes place starting from nearly the third day after the supernova explosion. A comparison of SN 1999em with SN 1987A reveals two very important results for supernova theory. First, the comparability of the helium core masses and the explosion energies implies a unique explosion mechanism for these core collapse supernovae. Second, the optimal model for SN 1999em is characterized by a weaker 56Ni mixing up to 660 km/s compared to a moderate 56Ni mixing up to 3000 km/s in SN 1987A, hydrogen being mixed deeply downward to 650 km/s.

SN 2004A: another Type II-P supernova with a red supergiant progenitor

We present a monitoring study of SN 2004A and probable discovery of a progenitor star in pre-explosion Hubble Space Telescope (HST) images. The photometric and spectroscopic monitoring of SN 2004A show that it was a normal Type II-P which was discovered in NGC 6207 about two weeks after explosion. We compare SN 2004A to the similar Type II-P SN 1999em and estimate an explosion epoch of 2004 January 6. We also calculate three new distances to NGC 6207 of 21.0 ± 4.3,-21.4 ± 3.5 and 25.1 ± 1.7-Mpc. The former was calculated using the Standard Candle Method (SCM) for SNe-II-P, and the latter two from the brightest supergiants method (BSM). We combine these three distances with existing kinematic distances, to derive a mean value of 20.3 ± 3.4-Mpc. Using this distance, we estimate that the ejected nickel mass in the explosion is 0.046+0.031−0.017-M⊙. The progenitor of SN 2004A is identified in pre-explosion WFPC2 F814W images with a magnitude of mF814W= 24.3 ± 0.3, but is below the detection limit of the F606W images. We show that this was likely a red supergiant (RSG) with a mass of 9+3−2-M⊙. The object is detected at 4.7σ above the background noise. Even if this detection is spurious, the 5σ upper limit would give a robust upper mass limit of 12-M⊙ for a RSG progenitor. These initial masses are very similar to those of two previously identified RSG progenitors of the Type II-P SNe 2004gd (8+4−2-M⊙) and 2005cs (9+3−2-M⊙).

Optical observations of type-IIP supernova 2004dj: Evidence for asymmetry of the 56Ni ejecta

Photometric and spectroscopic observations of the nearby type-IIP supernova 2004dj are presented. The 56Ni mass in the envelope of SN 2004dj was estimated from the light curve to be ≈0.02M⊙. This estimate is confirmed by modeling the Hα luminosity. The Hα emission line exhibits a strong asymmetry characterized by the presence of a blue component in the line with a shift of −1600 km s−1 at the early nebular phase. A similar asymmetry was found in the Hβ, [O I], and [Ca II] lines. The line asymmetry is interpreted as being the result of asymmetric 56Ni ejecta. The Hα profile and its evolution are reproduced in the model of an asymmetric bipolar 56Ni structure for a spherical hydrogen distribution. The mass of the front 56Ni jet is comparable to that of the central component and twice that of the rear 56Ni jet. We point out that the asymmetric bipolar structure of 56Ni ejecta is also present in SN 1999em, a normal type-IIP supernova.

Parameters of the classical type-IIP supernova SN 1999em

Based on observations of SN 1999em, we determined the physical parameters of this supernova using hydrodynamic calculations including nonequilibrium radiative transfer. Taking the distance to SN 1999em estimated by the expanding photosphere method (EPM) to be D = 7.5 Mpc, we found the parameters of the presupernova: radius R = 450R⊙, mass M = 15M⊙, and explosion energy E = 7 × 1050 erg. For the distance D = 12 Mpc determined from Cepheids, R, M, and E must be increased to the following values: R = 1000R⊙, M = 18M⊙, and E = 1051 erg. We show that one cannot restrict oneself to using the simple analytical formulas relating the supernova and presupernova parameters to obtain reliable parameters for type-IIP presupernovae.

A study of the Type II-P supernova 2003gd in M74

We present photometric and spectroscopic data of the type II-P supernova 2003gd, which was discovered in M74 close to the end of its plateau phase. SN 2003gd is the first type II supernova to have a directly confirmed red supergiant progenitor. We compare SN 2003gd with SN 1999em, a similar type II-P supernova, and estimate an explosion date of 18th March 2003. We determine a reddening towards the supernova of E(B-V) = 0.14+/-0.06, using three different methods. We also calculate three new distances to M74 of 9.6+/-2.8 Mpc, 7.7+/-1.7 Mpc and 9.6+/-2.2 Mpc. The former was estimated using the Standardised Candle Method (SCM), for type II supernovae, and the latter two using the Brightest Supergiants Method (BSM). When combined with existing kinematic and BSM distance estimates, we derive a mean value of 9.3+/-1.8 Mpc. SN 2003gd was found to have a lower tail luminosity compared to other ``normal'' type II-P SNe bringing into question the nature of this supernova. We present a discussion concluding that this is a ``normal'' type II-P supernova which is consistent with the observed progenitor mass of 8(+4/-2) Mo.