Downloading data using HttpClient
You are making your class variables readonly which is good because they won't change.

what I don't like is your mixing of the bracing style. Sometimes you use the Allman style, sometimes the K&amp;R and sometimes another style.
Usually in C# one would expect to see Allman style only. If you want to use another style, that is pretty fine as long as you stick to it.

the exception handling like you are doing it is superfluous and is destroying the stacktrace. Please read: is-there-a-difference-between-throw-and-throw-ex
Because you are never handling the exceptions you could just remove the try..catch completely.