A Measurement of the Rate of Type Ia Supernovae at Redshift z ≈ 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 -->?m = 0.3 = 1 ? ??, 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 h370 yr ?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)?, we obtain a value of -->? = 1.5 ? 0.6, i.e., the SN Ia rate is determined to be an increasing function of redshift at the ~2.5 ? level. Fitting the results to a model in which the volumetric SN rate is rV = A?(t) + B(t)$rV = Aρ (t) + Bd{ρ }(t) $ -->, where -->? (t) is the stellar mass density and (t)$d{ρ }(t) $ --> is the star formation rate, we find -->A = (2.8 ? 1.2) ? 10?14 SNe M?1? yr ?1, -->B = (9.3+ 3.4?3.1) ? 10?4 SNe M?1?.