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Register a new userThe Carnegie Supernova Project II. Observations of the intermediate luminosity red transient SNhunt120
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Maximilian Stritzinger
Publication date
2020
fields
Physics
and research's language is
English
Authors
M. D. Stritzinger
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We present multi-wavelength observations of two gap transients followed by the Carnegie Supernova Project-II and supplemented with data obtained by a number of different programs. Here in the first of two papers, we focus on the intermediate luminosity red transient (ILRT) designated SNhunt120, while in a companion paper we examine the luminous red novae AT 2014ej. Our data set for SNhunt120 consists of an early optical discovery, estimated to be within 3 days after outburst, the subsequent optical and near-infrared broadband followup extending over a $sim$2 month period, two visual- and two near-infrared wavelength spectra, and Spitzer Space Telescope observations extending from early ($+$28 d) to late ($+$1155 d) phases. SNhunt120 resembles other ILRTs such as NGC 300-2008-OT and SN 2008S, and like these other ILRTs, SNhunt120 exhibits prevalent mid-infrared emission at both early and late phases. From the comparison of SNhunt120 and other ILRTs to electron-capture supernova simulations, we find that the current models underestimate the explosion kinetic energy and thereby produce synthetic light curves that over-estimate the luminosity. Finally, examination of pre-outburst Hubble Space Telescope images yields no progenitor detection.
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We present optical and near-infrared broadband photometry and optical spectra of AT 2014ej from the the Carnegie Supernova Project-II. These observations are complemented with data from the CHilean Automatic Supernova sEarch, the Public ESO Spectroscopic Survey of Transient Objects, and from the Backyard Observatory Supernova Search. Observational signatures of AT 2014ej reveal that it is similar to other members of the gap-transient subclass known as luminous red novae (LRNe), including the ubiquitous double hump light curve and spectral properties akin to the LRN SN 2017jfs. A medium-dispersion, visual-wavelength spectrum of AT 2014ej taken the Magellan Clay telescope, exhibits a P Cygni H$alpha$ feature characterized by a blue velocity at zero intensity of $approx 110$ km s$^{-1}$ and a P Cygni minimum velocity of $approx70$ km s$^{-1}$, and which we attribute to emission from a circumstellar wind. Inspection of pre-outbust Hubble Space Telescope images yields no conclusive progenitor detection. In comparison with a sample of LRNe from the literature, AT 2014ej lies among the brighter end of the luminosity distribution. Comparison of the ultra-violet, optical, infrared (UVOIR) light curves of well-observed LRNe to common-envelope evolution models from the literature, indicates the models under predict the luminosity of the comparison sample at all phases and also produce inconsistent time-scales of the secondary peak. Future efforts to model LRNe should expand upon the current parameter space explored and therefore may consider more massive systems and a wider range of dynamical timescales.
We present $81$ near-infrared (NIR) spectra of $30$ Type II supernovae (SNe II) from the Carnegie Supernova Project-II (CSP-II), the largest such dataset published to date. We identify a number of NIR features and characterize their evolution over time. The NIR spectroscopic properties of SNe II fall into two distinct groups. This classification is first based on the strength of the He I $lambda1.083,mu$m absorption during the plateau phase; SNe II are either significantly above (spectroscopically strong) or below $50$ angstroms (spectroscopically weak) in pseudo equivalent width. However between the two groups, other properties, such as the timing of CO formation and the presence of Sr II, are also observed. Most surprisingly, the distinct weak and strong NIR spectroscopic classes correspond to SNe II with slow and fast declining light curves, respectively. These two photometric groups match the modern nomenclature of SNe IIP and IIL. Including NIR spectra previously published, 18 out of 19 SNe II follow this slow declining-spectroscopically weak and fast declining-spectroscopically strong correspondence. This is in apparent contradiction to the recent findings in the optical that slow and fast decliners show a continuous distribution of properties. The weak SNe II show a high-velocity component of helium that may be caused by a thermal excitation from a reverse-shock created by the outer ejecta interacting with the red supergiant wind, but the origin of the observed dichotomy is not understood. Further studies are crucial in determining whether the apparent differences in the NIR are due to distinct physical processes or a gap in the current data set.
Supernova LSQ13abf was discovered soon after explosion by the La Silla-QUEST Survey and followed by the CSP II at optical and near-IR wavelengths. Our analysis indicates LSQ13abf was discovered within two days of explosion and its first 10 days of evolution reveal a B-band light curve with an abrupt drop in luminosity. Contemporaneously, the V-band light curve exhibits a rise towards a first peak and the r- and i-band light curves show no early peak. The early light-curve evolution of LSQ13abf is reminiscent of the post explosion cooling phase observed in the Type Ib SN 2008D, and the similarity between the two objects extends over weeks. Spectroscopically, LSQ13abf resembles SN 2008D with P Cygni He I features that strengthen over time. Spectral energy distributions are constructed from broad-band photometry, and by fitting black-body (BB) functions a UVOIR light curve is constructed, and the underlying BB-temperature and BB-radius profiles are estimated. Explosion parameters are estimated by simultaneously fitting an Arnett model to the UVOIR light curve and the velocity evolution derived from spectral features, and a post-shock breakout cooling model to the first two epochs of the bolometric evolution. This combined model suggests an explosion energy of 1.3x10$^{51}$ ergs, a relatively high ejecta mass of 5.94 M$_{odot}$, a Ni mass of 0.16 M$_{odot}$, and a progenitor-star radius of 28.0 R$_{odot}$. The ejecta mass suggests the origins of LSQ13abf lie with a >25 M$_{odot}$ ZAMS progenitor and its radius is three and nine times larger than values estimated from the same analysis applied to observations of SNe 2008D and 1999ex, respectively. Alternatively, comparison of hydrodynamical simulations of >20-25 M$_{odot}$ ZAMS progenitors that evolve to pre-SN envelope masses around 10 M$_{odot}$ and extended (~100 R$_{odot}$) envelopes also match the observations of LSQ13abf.
Stripped-envelope (SE) supernovae (SNe) include H-poor (Type IIb), H-free (Type Ib) and He-free (Type Ic) events thought to be associated with the deaths of massive stars. The exact nature of their progenitors is a matter of debate. Here we present the analysis of the light curves of 34 SE SNe published by the Carnegie Supernova Project (CSP-I), which are unparalleled in terms of photometric accuracy and wavelength range. Light-curve parameters are estimated through the fits of an analytical function and trends are searched for among the resulting fit parameters. We found a tentative correlation between the peak absolute $B$-band magnitude and $Delta m_{15}(B)$, as well as a correlation between the late-time linear slope and $Delta m_{15}$. Making use of the full set of optical and near-IR photometry, combined with robust host-galaxy extinction corrections, bolometric light curves are constructed and compared to both analytic and hydrodynamical models. From the hydrodynamical models we obtained ejecta masses of $1.1-6.2$ $M_{odot}$, $^{56}$Ni masses of $0.03-0.35$ $M_{odot}$, and explosion energies (excluding two SNe Ic-BL) of $0.25-3.0times10^{51}$ erg. Our analysis indicates that adopting $kappa = 0.07$ cm$^{2}$ g$^{-1}$ as the mean opacity serves to be a suitable assumption when comparing Arnett-model results to those obtained from hydrodynamical calculations. We also find that adopting He I and O I line velocities to infer the expansion velocity in He-rich and He-poor SNe, respectively, provides ejecta masses relatively similar to those obtained by using the Fe II line velocities. The inferred ejecta masses are compatible with intermediate mass ($M_{ZAMS} leq 20$ $M_{odot}$) progenitor stars in binary systems for the majority of SE SNe. Furthermore, the majority of our SNe is affected by significant mixing of $^{56}$Ni, particularly in the case of SNe Ic.
We present optical and near-infrared photometry and spectroscopy of the Type IIn supernova (SN) 2014ab, obtained by the Carnegie Supernova Project II (CSP-II) and initiated immediately after its optical discovery. We also present mid-infrared photometry obtained by the Wide-field Infrared Survey Explorer (WISE) satellite extending from 56 days prior to the optical discovery to over 1600 days. The light curve of SN 2014ab evolves slowly, while the spectra exhibit strong emission features produced from the interaction between rapidly expanding ejecta and dense circumstellar matter. The light curve and spectral properties are very similar to those of SN 2010jl. The estimated mass-loss rate of the progenitor of SN 2014ab is of the order of 0.1 Msun/yr under the assumption of spherically symmetric circumstellar matter and steady mass loss. Although the mid-infrared luminosity increases due to emission from dust, which is characterized by a blackbody temperature close to the dust evaporation temperature (~ 2000 K), no clear signatures of in situ dust formation within the cold dense shell located behind the forward shock are observed in SN 2014ab in early phases. Mid-infrared emission of SN 2014ab may originate from pre-existing dust located within dense circumstellar matter that is heated by the SN shock or shock-driven radiation. Finally, for the benefit of the community, we also present in an Appendix five near-infrared spectra of SN 2010jl obtained between 450 to 1300 days post discovery.
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