Quantifying Type Ia Supernovae K-correction Uncertainties

1. Eric Hsiao, Chris Pritchet, Andy Howell, Mark SullivanSupernova Legacy Survey (SNLS) Quantifying Type Ia Supernovae K-correction Uncertainties Matching Filters For a high redshift supernova, the rest frame B filter (blue curve) is matched with a different observed filter (red curves). The matched filter depends on the redshift. The k-correction essentially compares the fluxes in these two filters. The k-correction uncertainties are low at these matched redshifts, as k-corrections at these redshifts are essentially independent of the supernova spectrum. Zeropoint Spectra The SNLS uses the AB magnitude system. A cross-system k-correction is needed to obtain Johnson B magnitude. This requires the comparison of the zeropoint spectra for the two photometric systems. Template Spectra Nugent et al. (2002) developed a Type Ia supernova template spectrum for each epoch for a typical “Branch normal” supernova with stretch parameter s=1. Local Supernova Spectra The spectrum of local supernova 1999ee at 17 days after B band maximum is plotted as an example (red curve). The template spectrum of the same epoch is also plotted for comparison (grey curve). 1999ee is bluer than the template spectrum at this epoch. The template spectrum is then “mangled” to the correct colour, using only the colour information of the local supernova (black curve). The affects of “mangling” inside the B band filter are dramatic for peculiar supernovae. The spectra of 10 local supernovae around B band maximum are plotted. Template: green curves Branch normals: black curves 1991bg-like: red curves sub-luminous at maximum unusually red 1991T-like: blue curves over-luminous at maximum blue due to lack of CaII and SiII features • K-correction Difference Comparison • The k-corrections are computed for 4 observed filters: g’r’i’ z’ • The k-corrections are computed using: • (a) local supernova spectrum (1999ee) • (b) template spectrum • (c) mangled template spectrum • The k-correction difference comparisons: • (b-a) are plotted as dotted lines • (c-a) are plotted as solid lines • The k-correction differences between the local and the template spectra are reduced after “mangling.” • Future Work • K-correct to other rest frame filters • Different treatments for the nebular phase • Different templates for different sub-types of SNe Ia • Use the observed spectrum of a high redshift supernova to modify its k-correction • Website • The library of 278 local supernova spectra and the computed k-corrections are available at the following website: • http://www.astro.uvic.ca/~hsiao/kcorr Abstract K-correction calculations directly affect the Type Ia supernovae (SNe Ia) magnitude determination and therefore directly affect the determination of cosmological parameters. The intrinsic variations in the colours and the spectral features of SNe Ia complicate the k-correction calculations and introduce uncertainties. We gathered available flux-calibrated spectra of local SNe Ia. The k-corrections calculated using a local supernova spectrum are compared with the k-corrections calculated using a supernova template spectrum of the same epoch. The difference comparison provides a way to quantify the k-correction errors. Because the intrinsic colour of a high redshift supernova can be inferred from its stretch parameter, the supernova template spectrum is “mangled” to have the same colour as the local spectrum for each epoch. We show that the errors can be reduced by using the “mangled” template spectra for k-correction calculations.