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Register a new userThe UV/optical spectra of the Type Ia supernova SN 2010jn: a bright supernova with outer layers rich in iron-group elements
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Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of constraining both the time-dependent density profile of the SN ejecta and its stratification by element abundance which, in turn, may discriminate between different explosion mechanisms and progenitor classes. Here we present a detailed analysis of Hubble Space Telescope ultraviolet (UV) and ground-based optical spectra and light curves of the SN Ia SN 2010jn (PTF10ygu). SN 2010jn was discovered by the Palomar Transient Factory (PTF) 15 days before maximum light, allowing us to secure a time-series of four UV spectra at epochs from -11 to +5 days relative to B-band maximum. The photospheric UV spectra are excellent diagnostics of the iron-group abundances in the outer layers of the ejecta, particularly those at very early times. Using the method of Abundance Tomography we have derived iron-group abundances in SN 2010jn with a precision better than in any previously studied SN Ia. Optimum fits to the data can be obtained if burned material is present even at high velocities, including significant mass fractions of iron-group elements. This is consistent with the slow decline rate (or high stretch) of the light curve of SN 2010jn, and consistent with the results of delayed-detonation models. Early-phase UV spectra and detailed time-dependent series of further SNe Ia offer a promising probe of the nature of the SN Ia mechanism.
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We present the optical (UBVRI) and ultraviolet (Swift-UVOT) photometry, and optical spectroscopy of Type Ia supernova SN 2017hpa. We study broadband UV+optical light curves and low resolution spectroscopy spanning from $-13.8$ to $+108$~d from the maximum light in $B$-band. The photometric analysis indicates that SN 2017hpa is a normal type Ia with $Delta m_{B}(15) = 0.98pm0.16$ mag and $M_{B}=-19.45pm0.15$ mag at a distance modulus of $mu = 34.08pm0.09$ mag. The $(uvw1-uvv)$ colour evolution shows that SN 2017hpa falls in the NUV-blue group. The $(B-V)$ colour at maximum is bluer in comparison to normal type Ia supernovae. Spectroscopic analysis shows that the Si II 6355 absorption feature evolves rapidly with a velocity gradient, $dot{v}=128pm 7$ km s$^{-1}$ d$^{-1}$. The pre-maximum phase spectra show prominent C II 6580 {AA} absorption feature. The C II 6580 {AA} line velocity measured from the observed spectra is lower than the velocity of Si II 6355 {AA}, which could be due to a line of sight effect. The synthetic spectral fits to the pre-maximum spectra using syn++ indicate the presence of a high velocity component in the Si II absorption, in addition to a photospheric component. Fitting the observed spectrum with the spectral synthesis code TARDIS, the mass of unburned C in the ejecta is estimated to be $sim 0.019$~$M_{odot}$. The peak bolometric luminosity is $L^{bol}_{peak} = 1.43times10^{43}$ erg s$^{-1}$. The radiation diffusion model fit to the bolometric light curve indicates $0.61pm0.02$ $M_odot$ of $^{56}$Ni is synthesized in the explosion.
Extensive and independent observations of Type Ia supernova (SN Ia) SN 2013dy are presented, including a larger set of $UBVRI$ photometry and optical spectra from a few days before the peak brightness to $sim$ 200 days after explosion, and ultraviolet (UV) photometry spanning from $t approx -10$ days to $t approx +15$ days referring to the $B$ band maximum. The peak brightness (i.e., $M_{rm B} = -19.65 pm 0.40$ mag, $L_{rm max} = [1.95 pm 0.55] times 10^{43}$ erg s$^{-1}$) and the mass of synthesised $^{56}$Ni (i.e., $M$($^{56}$Ni) = 0.90 $pm$ 0.26 M$_{odot}$) are calculated, and they conform to the expectation for a SN Ia with a slow decline rate (i.e., $Delta m_{15}(B)$ = 0.90 $pm$ 0.03 mag, Phillips 1993). However, the near infrared (NIR) brightness of this SN (i.e., $M_{rm H} = -17.33 pm 0.30$ mag) is at least 1.0 mag fainter than usual. Besides, spectroscopy classification reveals that SN 2013dy resides on the border of core normal and shallow silicon subclasses in the Branch et al. (2009) classification scheme, or on the border of the normal velocity SNe Ia and 91T/99aa-like events in the Wang et al. (2009a) system. These suggest that SN 2013dy is a slow-declining SN Ia located on the transitional region of nominal spectroscopic subclasses and might not be a typical normal sample of SNe Ia.
We present photometry and time-series spectroscopy of the nearby type Ia supernova (SN Ia) SN 2015F over $-16$ days to $+80$ days relative to maximum light, obtained as part of the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). SN 2015F is a slightly sub-luminous SN Ia with a decline rate of $Delta m15(B)=1.35 pm 0.03$ mag, placing it in the region between normal and SN 1991bg-like events. Our densely-sampled photometric data place tight constraints on the epoch of first light and form of the early-time light curve. The spectra exhibit photospheric C II $lambda 6580$ absorption until $-4$ days, and high-velocity Ca II is particularly strong at $<-10$ days at expansion velocities of $simeq$23000kms. At early times, our spectral modelling with syn++ shows strong evidence for iron-peak elements (Fe II, Cr II, Ti II, and V II) expanding at velocities $>14000$ km s$^{-1}$, suggesting mixing in the outermost layers of the SN ejecta. Although unusual in SN Ia spectra, including V II in the modelling significantly improves the spectral fits. Intriguingly, we detect an absorption feature at $sim$6800 AA that persists until maximum light. Our favoured explanation for this line is photospheric Al II, which has never been claimed before in SNe Ia, although detached high-velocity C II material could also be responsible. In both cases the absorbing material seems to be confined to a relatively narrow region in velocity space. The nucleosynthesis of detectable amounts of Al II would argue against a low-metallicity white dwarf progenitor. We also show that this 6800 AA feature is weakly present in other normal SN Ia events, and common in the SN 1991bg-like sub-class.
We develop a new framework for use in exploring Type Ia Supernova (SN Ia) spectra. Combining Principal Component Analysis (PCA) and Partial Least Square analysis (PLS) we are able to establish correlations between the Principal Components (PCs) and spectroscopic/photometric SNe Ia features. The technique was applied to ~120 supernova and ~800 spectra from the Nearby Supernova Factory. The ability of PCA to group together SNe Ia with similar spectral features, already explored in previous studies, is greatly enhanced by two important modifications: (1) the initial data matrix is built using derivatives of spectra over the wavelength, which increases the weight of weak lines and discards extinction, and (2) we extract time evolution information through the use of entire spectral sequences concatenated in each line of the input data matrix. These allow us to define a stable PC parameter space which can be used to characterize synthetic SN Ia spectra by means of real SN features. Using PLS, we demonstrate that the information from important previously known spectral indicators (namely the pseudo-equivalent width (pEW) of Si II 5972 / Si II 6355 and the line velocity of S II 5640 / Si II 6355) at a given epoch, is contained within the PC space and can be determined through a linear combination of the most important PCs. We also show that the PC space encompasses photometric features like B or V magnitudes, B-V color and SALT2 parameters c and x1. The observed colors and magnitudes, that are heavily affected by extinction, cannot be reconstructed using this technique alone. All the above mentioned applications allowed us to construct a metric space for comparing synthetic SN Ia spectra with observations.
We present a study of the peculiar Type Ia supernova 2001ay (SN 2001ay). The defining features of its peculiarity are: high velocity, broad lines, and a fast rising light curve, combined with the slowest known rate of decline. It is one magnitude dimmer than would be predicted from its observed value of Delta-m15, and shows broad spectral features. We base our analysis on detailed calculations for the explosion, light curves, and spectra. We demonstrate that consistency is key for both validating the models and probing the underlying physics. We show that this SN can be understood within the physics underlying the Delta-m15 relation, and in the framework of pulsating delayed detonation models originating from a Chandrasekhar mass, white dwarf, but with a progenitor core composed of 80% carbon. We suggest a possible scenario for stellar evolution which leads to such a progenitor. We show that the unusual light curve decline can be understood with the same physics as has been used to understand the Delta-m15 relation for normal SNe Ia. The decline relation can be explained by a combination of the temperature dependence of the opacity and excess or deficit of the peak luminosity, alpha, measured relative to the instantaneous rate of radiative decay energy generation. What differentiates SN 2001ay from normal SNe Ia is a higher explosion energy which leads to a shift of the Ni56 distribution towards higher velocity and alpha < 1. This result is responsible for the fast rise and slow decline. We define a class of SN 2001ay-like SNe Ia, which will show an anti-Phillips relation.
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