Reading σ Back Out of a Confidence Interval

A researcher knows the population standard deviation $\sigma$ and uses it to build a 95% confidence interval for the population mean from a random sample of $n = 100$ observations:

$\text{CI} = \bar{x} \pm z^{*} \cdot \frac{\sigma}{\sqrt{n}}, \qquad z^{*} = 1.96$

The interval she reports is

$(46.08,\ 53.92)$

What is the population standard deviation $\sigma$?