The volumetric rate of normal type Ia supernovae in the local universe
  discovered by the Palomar Transient Factory
  We present the volumetric rate of normal type Ia supernovae (SNe Ia)
discovered by the Palomar Transient Factory (PTF). Using strict data-quality
cuts, and considering only periods when the PTF maintained a regular cadence,
PTF discovered 90 SNe Ia at $z\le0.09$ in a well-controlled sample over three
years of operation (2010-2012). We use this to calculate the volumetric rate of
SN Ia events by comparing this sample to simulations of hundreds of millions of
SN Ia light curves produced in statistically representative realisations of the
PTF survey. This quantifies the recovery efficiency of each PTF SN Ia event,
and thus the relative weighting of each event. From this, the volumetric SN Ia
rate was found to be
$r_v=2.43\pm0.29\,\text{(stat)}_{-0.19}^{+0.33}\text{(sys)}\times10^{-5}\,\text{SNe
yr}^{-1}\,\text{Mpc}^{-3}\, h_{70}^{3}$. This represents the most precise local
measurement of the SN Ia rate. We fit a simple SN Ia delay-time distribution
model, $\propto\mathrm{t}^{-\beta}$, to our PTF rate measurement combined with
a literature sample of rate measurements from surveys at higher-redshifts. We
find $\beta{\sim}1$, consistent with a progenitor channel governed by the
gravitational in-spiral of binary white dwarfs.
