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Register a new userSN 2005cg: Explosion Physics and Circumstellar Interaction of a Normal Type Ia Supernova in a Low-Luminosity Host
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Robert Quimby
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We present the spectral evolution, light curve, and corresponding interpretation for the normal-bright Type Ia Supernova 2005cg discovered by ROTSE-IIIc. The host is a low-luminosity (M_r = -16.75), blue galaxy with strong indications of active star formation and an environment similar to that expected for SNe Ia at high redshifts. Early-time (t ~ -10 days) optical spectra obtained with the HET reveal an asymmetric, triangular-shaped Si II absorption feature at about 6100 AA with a sharp transition to the continuum at a blue shift of about 24,000 km s^-1. By 4 days before maximum, the Si II absorption feature becomes symmetric with smoothly curved sides. Similar Si II profile evolution has previously been observed in other supernovae, and is predicted by some explosion models, but its significance has not been fully recognized. Although the spectra predicted by pure deflagration and delayed detonation models are similar near maximum light, they predict qualitatively different chemical abundances in the outer layers and thus give qualitatively different spectra at the earliest phases. The Si line observed in SN 2005cg at early times requires the presence of burning products at high velocities and the triangular shape is likely to be formed in an extended region of slowly declining Si abundance that characterizes delayed detonation models. The spectra show a high-velocity Ca II IR feature that coincides in velocity space with the Si II cutoff. This supports the interpretation that the Ca II is formed when the outer layers of the SN ejecta sweep up about 5 x 10^-3 M_sun of material within the progenitor system. (Abridged)
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We present observations of the Type Ia supernova 2003du and report the detectionof an unusual, high-velocity component in the Ca II infrared triplet, similar tofeatures previously observed in SN 2000cx and SN 2001el. This feature exhibits a large expansion velocity (~18,000 km/s) which is nearly constant between -7 and +2 days relative to maximum light, and disappears shortly thereafter. Otherthan this feature, the spectral evolution and light curve resemble those of a normal SN Ia. We find that the Ca II feature can plausibly be caused by a dense shell formed when circumstellar material of solar abundance is overrun by the rapidly expanding outermost layers of the SN ejecta. Model calculations show that the optical and infrared spectra are remarkably unaffected by the circumstellar interaction. In particular, no hydrogen lines are detectable in either absorption or emission. The only qualitatively different features are the strong, high-velocity feature in the Ca II IR-triplet, and a somewhat weaker O I feature near 7,300 AA. The morphology and time evolution of these features provide an estimate for the amount of accumulated matter and an indication of the mixing in the dense shell. We apply these diagnostic tools to SN 2003du and infer that about 2 x 10^{-2} M_sun of solar abundance material may have accumulated in a circumstellar shell prior to the observations. Furthermore, the early light curve data imply that the circumstellar material was originally very close to the progenitor system, perhaps from an accretion disk, Roche lobe or common envelope.
The Type~Ia supernova (SN~Ia) 2017cfd in IC~0511 (redshift z = 0.01209+- 0.00016$) was discovered by the Lick Observatory Supernova Search 1.6+-0.7 d after the fitted first-light time (FFLT; 15.2 d before B-band maximum brightness). Photometric and spectroscopic follow-up observations show that SN~2017cfd is a typical, normal SN~Ia with a peak luminosity MB ~ -19.2+-0.2 mag, Delta m15(B) = 1.16 mag, and reached a B-band maximum ~16.8 d after the FFLT. We estimate there to be moderately strong host-galaxy extinction (A_V = 0.39 +- 0.03 mag) based on MLCS2k2 fitting. The spectrum reveals a Si~II lambda 6355 velocity of ~11,200 kms at peak brightness. The analysis shows that SN~2017cfd is a very typical, normal SN Ia in nearly every aspect. SN~2017cfd was discovered very young, with multiband data taken starting 2 d after the FFLT, making it a valuable complement to the currently small sample (fewer than a dozen) of SNe~Ia with color data at such early times. We find that its intrinsic early-time (B - V)0 color evolution belongs to the blue population rather than to the distinct red population. Using the photometry, we constrain the companion star radius to be < 2.5 R_sun, thus ruling out a red-giant companion.
While interaction with circumstellar material is known to play an important role in Type IIn supernovae (SNe), analyses of the more common SNe IIP and IIL have not traditionally included interaction as a significant power source. However, recent campaigns to observe SNe within days of explosion have revealed narrow emission lines of high-ionization species in the earliest spectra of luminous SNe II of all subclasses. These flash ionization features indicate the presence of a confined shell of material around the progenitor star. Here we present the first low-luminosity (LL) SN to show flash ionization features, SN 2016bkv. This SN peaked at $M_V = -16$ mag and has H{alpha} expansion velocities under 1350 km/s around maximum light, placing it at the faint/slow end of the distribution of SNe IIP (similar to SN 2005cs). The light-curve shape of SN 2016bkv is also extreme among SNe IIP. A very strong initial peak could indicate additional luminosity from circumstellar interaction. A very small fall from the plateau to the nickel tail indicates unusually large production of radioactive nickel compared to other LL SNe IIP. A comparison between nebular spectra of SN 2016bkv and models raises the possibility that SN 2016bkv is an electron-capture supernova.
An extensive set of optical and NIR photometry and low-resolution spectra the Type Ia supernova (SN Ia) 2003du was obtained using a number of facilities. The observations started 13 days before B-band maximum light and continued for 480 days with exceptionally good time sampling. The optical photometry was calibrated through the S-correction technique. The UBVRIJHK light curves and the color indices of SN 2003du closely resemble those of normal SNe Ia. SN 2003du reached a B-band maximum of 13.49 (+/-0.02) mag on JD2452766.38 (+/-0.5). We derive a B-band stretch parameter of 0.988 (+/-0.003), which corresponds to dM15=1.02 (+/-0.05), indicative of a SN Ia of standard luminosity. The reddening in the host galaxy was estimated by three methods, and was consistently found to be negligible. We estimate a distance modulus of 32.79 (+/-0.15) mag to the host galaxy, UGC 9391. The peak UVOIR bolometric luminosity of 1.35(+/-0.20) 10^43 erg/s and Arnetts rule implies that M(Ni56)=0.68 (+/-0.14)M_sun of Ni56 was synthesized during the explosion. Modeling of the UVOIR bolometric light curve also indicates M(Ni56) in the range 0.6-0.8 M_sun. The spectral evolution of SN 2003du at both optical and NIR wavelengths also closely resembles normal SNe Ia. In particular, the Si II ratio at maximum R(Si II)=0.22 (+/-0.02) and the time evolution of the blueshift velocities of the absorption line minima are typical. The pre-maximum spectra of SN 2003du showed conspicuous high-velocity features in the Ca II H&K doublet and infrared triplet, and possibly in Si II 6355, lines. We compare the time evolution of the profiles of these lines with other well-observed SNe Ia and we suggest that the peculiar pre-maximum evolution of Si II 6355 line in many SNe Ia is due to the presence of two blended absorption components.
Type II-linear supernovae are thought to arise from progenitors that have lost most of their H envelope by the time of the explosion, and they are poorly understood because they are only occasionally discovered. It is possible that they are intrinsically rare, but selection effects due to their rapid luminosity evolution may also play an important role in limiting the number of detections. In this context, the discovery of a subluminous type II-linear event is even more interesting. We investigate the physical properties and characterise the explosion site of the type II SN 1999ga, which exploded in the nearby spiral galaxy NGC 2442. Spectroscopic and photometric observations of SN 1999ga allow us to constrain the energetics of the explosion and to estimate the mass of the ejected material, shedding light on the nature of the progenitor star in the final stages of its life. The study of the environment in the vicinity of the explosion site provides information on a possible relation between these unusual supernovae and the properties of the galaxies hosting them. Despite the lack of early-time observations, we provide reasonable evidence that SN 1999ga was probably a type II-linear supernova that ejected a few solar masses of material, with a very small amount of radioactive elements of the order of 0.01 solar masses.
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