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Register a new userSiFTO: An Empirical Method for Fitting SNe Ia Light Curves
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We present SiFTO, a new empirical method for modeling type Ia supernovae (SNe Ia) light curves by manipulating a spectral template. We make use of high-redshift SN observations when training the model, allowing us to extend it bluer than rest frame U. This increases the utility of our high-redshift SN observations by allowing us to use more of the available data. We find that when the shape of the light curve is described using a stretch prescription, applying the same stretch at all wavelengths is not an adequate description. SiFTO therefore uses a generalization of stretch which applies different stretch factors as a function of both the wavelength of the observed filter and the stretch in the rest-frame B band. We compare SiFTO to other published light-curve models by applying them to the same set of SN photometry, and demonstrate that SiFTO and SALT2 perform better than the alternatives when judged by the scatter around the best fit luminosity distance relationship. We further demonstrate that when SiFTO and SALT2 are trained on the same data set the cosmological results agree.
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We present a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe~Ia). We find that a variant broken-power-law function provides a good fit, with the simple assumption that the optical emission is approximately the blackbody emission of the expanding fireball. This function is mathematically analytic and is derived directly from the photospheric velocity evolution. When deriving the function, we assume that both the blackbody temperature and photospheric velocity are constant, but the final function is able to accommodate these changes during the fitting procedure. Applying it to the case study of SN~2011fe gives a surprisingly good fit that can describe the light curves from the first-light time to a few weeks after peak brightness, as well as over a large range of fluxes ($sim 5$, mag, and even $sim 7$,mag in the $g$ band). Since SNe~Ia share similar light-curve shapes, this fitting method has the potential to fit most other SNe~Ia and characterize their properties in large statistical samples such as those already gathered and in the near future as new facilities become available.
We investigate a new empirical fitting method for the optical light curves of Type Ia supernovae (SNe~Ia) that is able to estimate the first-light time of SNe~Ia, even when they are not discovered extremely early. With an improved ability to estimate the time of first light for SNe Ia, we compute the rise times for a sample of 56 well-observed SNe~Ia. We find rise times ranging from 10.5 to 20.5 days, with a mean of 16.0 days, and confirm that the rise time is generally correlated with the decline rate $Delta m_{15}(B)$, but with large scatter. The rise time could be an additional parameter to help classify SN~Ia subtypes.
We examine the relationship between three parameters of Type Ia supernovae (SNe~Ia): peak magnitude, rise time, and photospheric velocity at the time of peak brightness. The peak magnitude is corrected for extinction using an estimate determined from MLCS2k2 fitting. The rise time is measured from the well-observed $B$-band light curve with the first detection at least 1~mag fainter than the peak magnitude, and the photospheric velocity is measured from the strong absorption feature of Si~II~$lambda$6355 at the time of peak brightness. We model the relationship among these three parameters using an expanding fireball with two assumptions: (a) the optical emission is approximately that of a blackbody, and (b) the photospheric temperatures of SNe~Ia are similar to each other at the time of peak brightness. We compare the precision of the distance residuals inferred using this physically motivated model against those from the empirical Phillips relation and the MLCS2k2 method for 47 low-redshift SNe~Ia ($0.005 < z< 0.04$) and find comparable scatter. However, SNe~Ia in our sample with higher velocities are inferred to be intrinsically fainter. Eliminating the high-velocity SNe and applying a more stringent extinction cut to obtain a low-v-golden sample of 22 SNe, we obtain significantly reduced scatter in the new relation, better than those of the Phillips relation and the MLCS2k2 method. After removing model peculiar velocities, our final scatter for the new relation is $0.108 pm 0.018$~mag.
We present an analysis of high precision V light curves (LC) for 18 local Type Ia Supernovae, SNe Ia, as obtained with the same telescope and setup at the Las Campanas Observatory (LCO). This homogeneity provides an intrinsic accuracy a few hundreds of a magnitude both with respect to individual LCs and between different objects. Based on the Single Degenerate Scenario, SD, we identify patterns which have been predicted by model calculations as signatures of the progenitor and accretion rate which change the explosion energy and the amount of electron capture, respectively. Using these templates as principle components and the overdetermined system of SN pairs, we reconstruct the properties of progenitors and progenitor systems. All LCO SNe Ia follow the brightness decline relation but 2001ay. After subtraction of the two components, the remaining scatter is reduced to 0.01-0.03m. Type SNe Ia seem to originate from progenitors with Main Sequence masses of 3Mo with the exception of two subluminous SNe Ia with < 2Mo. The component analysis indicates a wide range of accretion rates in the progenitor systems closing the gap to accretion induced collapses (AIC). SN1991t-like objects show differences in $dm15$ but no tracers of our secondary parameters. This may point to a different origin such as DD-Scenario or the Pulsating Delayed Detonations. SN2001ay does not follow the decline relation. It can be understood in the framework of C-rich WDs, and this group may produce an anti-Phillips relation. We suggest that this may be a result of a common envelope phase and mixing during central He burning as in SN1987A.
We present a revised SALT2 surface (`SALT2-2021) for fitting the light curves of Type Ia supernovae (SNe Ia), which incorporates new measurements of zero-point calibration offsets and Milky Way extinction. The most notable change in the new surface occurs in the UV region. This new surface alters the distance measurements of SNe~Ia, which can be used to investigate the nature of dark energy by probing the expansion history of the Universe. Using the revised SALT2 surface on public data from the first three years of the Dark Energy Survey Supernova Program (combined with an external low-$z$ SNe Ia sample) and combining with cosmic microwave background constraints, we find a change in the dark energy equation of state parameter, $Delta w = 0.015 pm 0.004$. This result highlights the continued importance of controlling and reducing systematic uncertainties, particularly with the next generation of supernova analyses aiming to improve constraints on dark energy properties.
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