Where can I find the samples of scale parameter for basehaz of weibull in rstanarm::stanjm()?

Modeling
1

I would like to retrieve the fitted suvival values from rstanarm::stan_jm(). The base hazard is weibull. However, I can only find the shape parameter. How can I get the scale parameter?

For example, in the model below

modelc = stan_jm(formulaLong = logBili ~ year + (1 | id), 
              dataLong = pbcLong,
              formulaEvent = Surv(futimeYears, death) ~ sex + trt, 
              dataEvent = pbcSurv,
              time_var = "year",
              basehaz = "weibull",
              ...)
draws <- as.data.frame(modelc)

The draws return all MCMC samples for model fitting. However, I can only find

Event|weibull-shape

as a column name in draws. Where is the scale?
BTW, is the scale parameter as \sigma in the format of (\alpha/\sigma)(t/\sigma)^{\alpha-1}, or as \lambda in the format of \alpha\lambda^\alpha t^{\alpha-1}, or as \Lambda in the format of \Lambda t^{\alpha-1}? The formulas above are all weibull hazard, just in different expression.
Thanks!