How to get variance of estimated coefficients of AR model?

Question

I have time series data $y$. I use ar.ols to fit $y$, but how can I get variance of estimated coefficients in R. By the way, I check the return object ar_model = ar.ols(y) of ar.ols, is ar_model$var.pred estimated variance of residual $\sigma^2$?

Thanks in advance!