2008ApJ...682..262D

We present a measurement of the rate of Type Ia supernovae (SNe Ia) from the first of three seasons of data from the SDSS-II Supernova Survey. For this measurement, we include 17 SNe Ia at redshift z≤0.12. Assuming a flat cosmology with Ω_m=0.3=1-Ω_Λ, we find a volumetric SN Ia rate of [2.93^+0.17_–0.04(systematic)^+0.90_–0.71(statistical)]x10^–5 SNe Mpc^–3 h³₇₀/yr, at a volume-weighted mean redshift of 0.09. This result is consistent with previous measurements of the SN Ia rate in a similar redshift range. The systematic errors are well controlled, resulting in the most precise measurement of the SN Ia rate in this redshift range. We use a maximum likelihood method to fit SN rate models to the SDSS-II Supernova Survey data in combination with other rate measurements, thereby constraining models for the redshift evolution of the SN Ia rate. Fitting the combined data to a simple power-law evolution of the volumetric SN Ia rate, r_V∝(1+z)^β, we obtain a value of β=1.5±0.6, i.e., the SN Ia rate is determined to be an increasing function of redshift at the ∼2.5 σ level. Fitting the results to a model in which the volumetric SN rate is r_V=Aρ(t)+Bρ{dot}(t), where ρ(t) is the stellar mass density and ρ{dot}(t) is the star formation rate, we find A=(2.8±1.2)x10^–14 SNe M^–1_☉/yr, B=(9.3^+3.4_–3.1)x10^–4 SNe M^–1_☉.