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Register a new userExtraordinary Late-Time Infrared Emission of Type IIn Supernovae
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Added by
Christopher L. Gerardy
Publication date
2002
fields
Physics
and research's language is
English
Authors
C. L. Gerardy
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Near-Infrared (NIR) observations are presented for five Type IIn supernovae (SN 1995N, SN 1997ab, SN 1998S, SN 1999Z, and SN 1999el) that exhibit strong infrared excesses at late times (t >= 100 d). H- and K-band emission from these objects is dominated by a continuum that rises toward longer wavelengths. The data are interpreted as thermal emission from dust, probably situated in a pre-existing circumstellar nebula. The IR luminosities implied by single temperature blackbody fits are quite large,> 10^(41 - 42) erg s^-1, and the emission evolves slowly, lasting for years after maximum light. For SN 1995N, the integrated energy release via IR dust emission was 0.5 -- 1 * 10^50 erg. A number of dust heating scenarios are considered, the most likely being an infrared echo poweredby X-ray and UV emissions from the shock interaction with a dense circumstellar medium.
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The Type IIn supernovae (SNe IIn) have been found to be associated with significant amounts of dust. These core-collapse events are generally expected to be the final stage in the evolution of highly-massive stars, either while in an extreme red supergiant phase or during a luminous blue variable phase. Both evolutionary scenarios involve substantial pre-supernova mass loss. I have analyzed the SN IIn 1995N in MCG -02-38-017 (Arp 261), for which mid-infrared archival data obtained with the Spitzer Space Telescope in 2009 (~14.7 yr after explosion) and with the Wide-field Infrared Survey Explorer (WISE) in 2010 (~15.6--16.0 yr after explosion) reveal a luminous (~2e7 L_sun) source detected from 3.4 to 24 micron. These observations probe the circumstellar material, set up by pre-SN mass loss, around the progenitor star and indicate the presence of ~0.05--0.12 M_sun of pre-existing, cool dust at ~240 K. This is at least a factor ~10 lower than the dust mass required to be produced from SNe at high redshift, but the case of SN 1995N lends further evidence that highly massive stars could themselves be important sources of dust.
We study iPTF14hls, a luminous and extraordinary long-lived Type II supernova, which lately has attracted much attention and disparate interpretation. We present new optical photometry that extends the light curves until more than 3 yr past discovery. We also obtained optical spectroscopy over this period, and furthermore present additional space-based observations using Swift and HST. After an almost constant luminosity for hundreds of days, the later light curve of iPTF14hls finally fades and then displays a dramatic drop after about 1000 d, but the supernova is still visible at the latest epochs presented. The spectra have finally turned nebular, and the very last optical spectrum likely displays signatures from the deep and dense interior of the explosion. The high-resolution HST image highlights the complex environment of the explosion in this low-luminosity galaxy. We provide a large number of additional late-time observations of iPTF14hls, which are (and will continue to be) used to assess the many different interpretations for this intriguing object. In particular, the very late (+1000 d) steep decline of the optical light curve, the lack of very strong X-ray emission, and the emergence of intermediate-width emission lines including of [S II] that likely originate from dense, processed material in the core of the supernova ejecta, are all key observational tests for existing and future models.
We examine the late-time (t > 200 days after peak brightness) spectra of Type Iax supernovae (SNe Iax), a low-luminosity, low-energy class of thermonuclear stellar explosions observationally similar to, but distinct from, Type Ia supernovae. We present new spectra of SN 2014dt, resulting in the most complete published late-time spectral sequence of a SN Iax. At late times, SNe Iax have generally similar spectra, all with a similar continuum shape and strong forbidden-line emission. However, there is also significant diversity where some late-time SN Iax spectra display narrow P-Cygni features and a continuum indicative of a photosphere in addition to strong narrow forbidden lines, while others have no obvious P-Cygni features, strong broad forbidden lines, and weak narrow forbidden lines. Finally, some SNe Iax have spectra intermediate to these two varieties with weak P-Cygni features and broad/narrow forbidden lines of similar strength. We find that SNe Iax with strong broad forbidden lines also tend to be more luminous and have higher-velocity ejecta at peak brightness. We estimate blackbody and kinematic radii of the late-time photosphere, finding the latter an order of magnitude larger than the former. We propose a two-component model that solves this discrepancy and explains the diversity of the late-time spectra of SNe Iax. In this model, the broad forbidden lines originate from the SN ejecta, while the photosphere, P-Cygni lines, and narrow forbidden lines originate from a wind launched from the remnant of the progenitor white dwarf and is driven by the radioactive decay of newly synthesized material left in the remnant. The relative strength of the two components accounts for the diversity of late-time SN Iax spectra. This model also solves the puzzle of a long-lived photosphere and slow late-time decline of SNe Iax. (Abridged)
Ground-based optical spectra and Hubble Space Telescope images of ten core-collapse supernovae (CCSNe) obtained several years to decades after outburst are analyzed with the aim of understanding the general properties of their late-time emissions. New observations of SN 1957D, 1970G, 1980K, and 1993J are included as part of the study. Blueshifted line emissions in oxygen and/or hydrogen with conspicuous line substructure are a common and long-lasting phenomenon in the late-time spectra. Followed through multiple epochs, changes in the relative strengths and velocity widths of the emission lines are consistent with expectations for emissions produced by interaction between SN ejecta and the progenitor stars circumstellar material. The most distinct trend is an increase in the strength of [O III]/([O I]+[O II]) with age, and a decline in Halpha/([O I]+[O II]) which is broadly consistent with the view that the reverse shock has passed through the H envelope of the ejecta in many of these objects. We also present a spatially integrated spectrum of the young Galactic supernova remnant Cassiopeia A (Cas A). Similarities observed between the emission line profiles of the 330 yr old Cas A remnant and decades old CCSNe suggest that observed emission line asymmetry in evolved CCSN spectra may be associated with dust in the ejecta, and that minor peak substructure typically interpreted as clumps or blobs of ejecta may instead be linked with large-scale rings of SN debris.
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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