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Register a new userThe Nearby Type Ibn Supernova 2015G: Signatures of Asymmetry and Progenitor Constraints
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We present the results of an extensive observational campaign on the nearby Type Ibn SN 2015G, including data from radio through ultraviolet wavelengths. SN 2015G was asymmetric, showing late-time nebular lines redshifted by ~1000 km/s. It shared many features with the prototypical SN In 2006jc, including extremely strong He I emssion lines and a late-time blue pseudocontinuum. The young SN 2015G showed narrow P-Cygni profiles of He I, but never in its evolution did it show any signature of hydrogen - arguing for a dense, ionized, and hydrogen-free circumstellar medium moving outward with a velocity of ~1000 km/s and created by relatively recent mass loss from the progenitor star. Ultraviolet through infrared observations show that the fading SN 2015G (which was probably discovered some 20 days post-peak) had a spectral energy distribution that was well described by a simple, single-component blackbody. Archival HST images provide upper limits on the luminosity of SN 2015Gs progenitor, while nondetections of any luminous radio afterglow and optical nondetections of outbursts over the past two decades provide constraints upon its mass-loss history.
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We present photometric and spectroscopic observations of the type Ibn supernova (SN) 2019uo, the second ever SN Ibn with flash ionization (He II, C III, N III) features in its early spectra. SN 2019uo displays a rapid post-peak luminosity decline of 0.1 mag d$^{-1}$ similar to most of the SNe Ibn, but is fainter ($M^V_{max} = -18.30 pm 0.24$ mag) than a typical SN Ibn and shows a color evolution that places it between SNe Ib and the most extreme SNe Ibn. SN 2019uo shows P-cygni He I features in the early spectra which gradually evolves and becomes emission dominated post peak. It also shows faster evolution in line velocities as compared to most other members of the type Ibn subclass. The bolometric light curve is fairly described by a $^{56}$Ni + circumstellar interaction model.
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.
We present late-time observations of the site of the Type Ibn supernova (SN) 2006jc acquired with the Hubble Space Telescope Advanced Camera for Surveys. A faint blue source is recovered at the SN position with brightness $m_{F435W}=26.76pm0.20$, $m_{F555W}=26.60pm0.23$ and $m_{F625W} = 26.32pm0.19$ mags, although there is no detection in a contemporaneous narrow-band $mathrm{Halpha}$ image. The spectral energy distribution of the late-time source is well fit by a stellar-like spectrum ($log T_{eff} > 3.7$ and $log L / L_{odot} > 4$) subject to only a small degree of reddening consistent with that estimated for SN~2006jc itself at early-times. The lack of further outbursts after the explosion of SN~2006jc suggests that the precursor outburst originated from the progenitor. The possibility of the source being a compact host cluster is ruled out on the basis of the sources faintness, however the possibility that the late-time source maybe an unresolved light echo originating in a shell or sphere of pre-SN dust (within a radius $1mathrm{pc}$) is also discussed. Irrespective of the nature of the late-time source, these observations rule out a luminous blue variable as a companion to the progenitor of SN~2006jc.
We present photometric and spectroscopic follow-up observations of the highly luminous Type Ibn supernova ASASSN-14ms, which was discovered on UT 2014-12-26.61 at $m_V sim 16.5$. With a peak absolute $V$-band magnitude brighter than $-20.5$, a peak bolometric luminosity of $1.7 times 10^{44}$ ergs s$^{-1}$, and a total radiated energy of $2.1 times 10^{50}$ ergs, ASASSN-14ms is one of the most luminous Type Ibn supernovae yet discovered. In simple models, the most likely power source for this event is a combination of the radioactive decay of $^{56}$Ni and $^{56}$Co at late times and the interaction of supernova ejecta with the progenitors circumstellar medium at early times, although we cannot rule out the possibility of a magnetar-powered light curve. The presence of a dense circumstellar medium is indicated by the intermediate-width He I features in the spectra. The faint ($m_g sim 21.6$) host galaxy SDSS J130408.52+521846.4 has an oxygen abundance below $12+log(O/H) lesssim 8.3$, a stellar mass of $M_* sim 2.6 times 10^8 M_{odot}$, and a star formation rate of $textrm{SFR} sim 0.02$ $M_{odot}$ yr$^{-1}$.
We present an early-phase $g$-band light curve and visual-wavelength spectra of the normal Type Ia supernova (SN) 2013gy. The light curve is constructed by determining the appropriate S-corrections to transform KAIT natural-system $B$- and $V$-band photometry and Carnegie Supernova Project natural-system $g$-band photometry to the Pan-STARRS1 $g$-band natural photometric system. A Markov Chain Monte Carlo calculation provides a best-fit single power-law function to the first ten epochs of photometry described by an exponent of $2.16^{+0.06}_{-0.06}$ and a time of first light of MJD 56629.4$^{+0.1}_{-0.1}$, which is $1.93^{+0.12}_{-0.13}$ days (i.e., $<48$~hr) before the discovery date (2013 December 4.84 UT) and $-19.10^{+0.12}_{-0.13}$ days before the time of $B$-band maximum (MJD 56648.5$pm0.1$). The estimate of the time of first light is consistent with the explosion time inferred from the evolution of the Si II $lambda$6355 Doppler velocity. Furthermore, discovery photometry and previous nondetection limits enable us to constrain the companion radius down to $R_c leq 4,R_{odot}$. In addition to our early-time constraints, we use a deep +235 day nebular-phase spectrum from Magellan/IMACS to place a stripped H-mass limit of $< 0.018,M_{odot}$. Combined, these limits effectively rule out H-rich nondegenerate companions.
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