A Measurement of the Rate of Type Ia Supernovae at Redshiftz≈ 0.1 from the First Season of the SDSS‐II Supernova Survey

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 Ωₘ = 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)] × 10⁻⁵ SNe Mpc⁻³ h₇₀³ year⁻¹, 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, rV ∝ (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, rV=Aρ(t)+B ρ(t), where ρ(t) is the stellar mass density and ρ(t) is the star formation rate, we find A = (2.8 ± 1.2) × 10⁻¹⁴ SNe M_⁻¹ year⁻¹, B = (9.3+3.4-3.1)× 10⁻⁴ SNe M_⁻¹.