Ruby - time.now in UTC [duplicate]

Possible Duplicate:
How do I Convert DateTime.now to UTC in Ruby?

How do I get current time in Date-time-milliseconds & UTC? Ex. 2012-03-22T18:48:40.873Z

I tried -

Time.now.utc_offset.to_s
Time.now.xs_datetime

Time.now.utc is what you must be using.