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Register a new userA systematic reclassification of type IIn supernovae
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Type IIn supernovae (SNe IIn) are a relatively infrequently observed subclass of SNe whose photometric and spectroscopic properties are varied. A common thread among SNe IIn are the complex multiple-component hydrogen Balmer lines. Owing to the heterogeneity of SNe IIn, online databases contain some outdated, erroneous, or even contradictory classifications. SN IIn classification is further complicated by SN impostors and contamination from underlying HII regions. We have compiled a catalogue of systematically classified nearby (redshift z < 0.02) SNe IIn using the Open Supernova Catalogue (OSC). We present spectral classifications for 115 objects previously classified as SNe IIn. Our classification is based upon results obtained by fitting multiple Gaussians to the H-alpha profiles. We compare classifications reported by the OSC and Transient Name Server (TNS) along with the best matched templates from SNID. We find that 28 objects have been misclassified as SNe IIn. TNS and OSC can be unreliable; they disagree on the classifications of 51 of the objects and contain a number of erroneous classifications. Furthermore, OSC and TNS hold misclassifications for 34 and twelve (respectively) of the transients we classify as SNe IIn. In total, we classify 87 SNe IIn. We highlight the importance of ensuring that online databases remain up to date when new or even contemporaneous data become available. Our work shows the great range of spectral properties and features that SNe IIn exhibit, which may be linked to multiple progenitor channels and environment diversity. We set out a classification sche me for SNe IIn based on the H-alpha profile which is not greatly affected by the inhomogeneity of SNe IIn.
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Type Ia supernovae are bright stellar explosions thought to occur when a thermonuclear runaway consumes roughly a solar mass of degenerate stellar material. These events produce and disseminate iron-peak elements, and properties of their light curves allow for standardization and subsequent use as cosmological distance indicators. The explosion mechanism of these events remains, however, only partially understood. Many models posit the explosion beginning with a deflagration born near the center of a white dwarf that has gained mass from a stellar companion. In order to match observations, models of this single-degenerate scenario typically invoke a subsequent transition of the (subsonic) deflagration to a (supersonic) detonation that rapidly consumes the star. We present an investigation into the systematics of thermonuclear supernovae assuming this paradigm. We utilize a statistical framework for a controlled study of two-dimensional simulations of these events from randomized initial conditions. We investigate the effect of the composition and thermal history of the progenitor on the radioactive yield, and thus brightness, of an event. Our results offer an explanation for some observed trends of mean brightness with properties of the host galaxy.
Observations suggest that some massive stars experience violent and eruptive mass loss associated with significant brightening that cannot be explained by hydrostatic stellar models. This event seemingly forms dense circumstellar matter (CSM). The mechanism of eruptive mass loss has not been fully explained. We focus on the fact that the timescale of nuclear burning gets shorter than the dynamical timescale of the envelope a few years before core collapse for some massive stars. To reveal the properties of the eruptive mass loss, we investigate its relation to the energy injection at the bottom of the envelope supplied by nuclear burning taking place inside the core. In this study, we do not specify the actual mechanism for transporting energy from the site of nuclear burning to the bottom of the envelope. Instead, we parameterize the amount of injected energy and the injection time and try to extract information on these parameters from comparisons with observations. We carried out 1-D radiation hydrodynamical simulations for progenitors of red, yellow, and blue supergiants, and Wolf-Rayet stars. We calculated the evolution of the progenitors with a public stellar evolution code. We obtain the light curve associated with the eruption, the amount of ejected mass, and the CSM distribution at the time of core-collapse. The energy injection at the bottom of the envelope of a massive star within a period shorter than the dynamical timescale of the envelope could reproduce some observed optical outbursts prior to the core-collapse and form the CSM, which can power an interaction supernova (SN) classified as type IIn.
Some massive stars experience episodic and intense mass loss phases with fluctuations in the luminosity. Ejected material forms circumstellar matter around the star, and the subsequent core collapse results in a Type IIn supernova that is characterized by interaction between supernova ejecta and circumstellar matter. The energy source that triggers these mass eruptions and dynamics of the outflow have not been clearly explained. Moreover, the mass eruption itself can alter the density structure of the envelope and affect the dynamics of the subsequent mass eruption if these events are repeated. A large amount of observational evidence suggests multiple mass eruptions prior to core collapse. We investigate the density structure of the envelope altered by the first mass eruption and the nature of the subsequent second mass eruption event in comparison with the first event. We deposited extra energy at the bottom of the hydrogen envelope of 15$M_odot$ stars twice and calculated the time evolution by radiation hydrodynamical simulation code. We did not deal with the origin of the energy source, but focused on the dynamics of repeated mass eruptions from a single massive star. There are significant differences between the first and second mass eruptions in terms of the luminosity and the color. The second eruption leads to a redder burst event in which the associated brightening phase lasts longer than the first. The amount of ejected matter is different even with the same deposited energy in the first and second event, but the difference depends on the density structure of the star. Upcoming high cadence and deep transient surveys will provide us a lot of pre-supernova activities, and some of which might show multi-peaked light curves. These should be interpreted taking the effect of density structure altered by the preceding outburst events into consideration.
Recent observations suggest that Type IIn supernovae (SNe IIn) may exhibit late-time (>100 days) infrared (IR) emission from warm dust more than other types of core-collapse SNe. Mid-IR observations, which span the peak of the thermal spectral energy distribution, provide useful constraints on the properties of the dust and, ultimately, the circumstellar environment, explosion mechanism, and progenitor system. Due to the low SN IIn rate (<10% of all core-collapse SNe), few IR observations exist for this subclass. The handful of isolated studies, however, show late-time IR emission from warm dust that, in some cases, extends for five or six years post-discovery. While previous Spitzer/IRAC surveys have searched for dust in SNe, none have targeted the Type IIn subclass. This article presents results from a warm Spitzer/IRAC survey of the positions of all 68 known SNe IIn within a distance of 250 Mpc between 1999 and 2008 that have remained unobserved by Spitzer more than 100 days post-discovery. The detection of late-time emission from ten targets (~15%) nearly doubles the database of existing mid-IR observations of SNe IIn. Although optical spectra show evidence for new dust formation in some cases, the data show that in most cases the likely origin of the mid-IR emission is pre-existing dust, which is continuously heated by optical emission generated by ongoing circumstellar interaction between the forward shock and circumstellar medium. Furthermore, an emerging trend suggests that these SNe decline at ~1000--2000 days post-discovery once the forward shock overruns the dust shell. The mass-loss rates associated with these dust shells are consistent with luminous blue variable (LBV) progenitors.
We present a systematic study of mid-infrared (mid-IR) emission from 141 nearby supernovae (SNe) observed with the InfraRed Array Camera (IRAC) on Spitzer.These SNe reside in one of the 190 galaxies within 20 Mpc drawn from the ongoing SPIRITS program. We detect 8 Type Ia SNe and 36 core-collapse SNe. All Type I SNe become undetectable within 3 years of explosion. About 22$pm$11% of Type II SNe continue to be detected at late-times. Dust luminosity, temperature, and a lower liit on mass are obtained by fitting the SED using photometry with IRAC bands 1 and 2. The mass estimate does not distinguish between pre-existing and newly produced dust. We observe warm dust masses between $10^{-2}$ and $10^{-6}$ $rm M_{odot}$ and dust temperatures from 200 K to 1280 K.We present detailed case studies of two extreme Type II-P SNe: SN 2011ja and 2014bi. SN 2011ja was over-luminous ([4.5] = -15.6 mag) at 900 days post-explosion accompanied by the growing dust mass. This suggests either an episode of dust formation or an intensifying CSM interactions heating up pre-existing dust. SN 2014bi showed a factor of 10 decrease in dust mass over one month suggesting either an episode of dust destruction or a fading source of dust heating. A rebrightening of the Type Ib SN 2014C is observed and attributed to CSM interactions. This observation adds to a small number of stripped-envelope SNe that have mid-IR excess. The observations suggest that the CSM shell around SN 2014C is originated from an LBV-like eruption roughly 100 years before the explosion. We also report detections of SN1974E, 1979C, 1980K, 1986J, and 1993J detected more than 20 years post-explosion. The number of outlying SNe identified in this work demonstrates the power of late time mid-IR observations of a large sample of SNe to identify events with unusual evolution.
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