Strongly Lensed Jets, Time Delays, and the Value of H0
  In principle, the most straightforward method of estimating the Hubble
constant relies on time delays between mirage images of strongly-lensed
sources. It is a puzzle, then, that the values of H0 obtained with this method
span a range from 50 - 100 km/s/Mpc. Quasars monitored to measure these time
delays, are multi-component objects. The variability may arise from different
components of the quasar or may even originate from a jet. Misidentifying a
variable emitting region in a jet with emission from the core region may
introduce an error in the Hubble constant derived from a time delay. Here, we
investigate the complex structure of sources as the underlying physical
explanation of the widespread in values of the Hubble constant based on
gravitational lensing. Our Monte Carlo simulations demonstrate that the derived
value of the Hubble constant is very sensitive to the offset between the center
of the emission and the center of the variable emitting region. Thus, we
propose using the value of H0 known from other techniques to spatially resolve
the origin of the variable emission once the time delay is measured. We
advocate this method particularly for gamma-ray astronomy, where the angular
resolution of detectors reaches approximately 0.1 degree; lensed blazars offer
the only route for identify the origin of gamma-ray flares. Large future
samples of gravitationally lensed sources identified with Euclid, SKA, and LSST
will enable a statistical determination of H0.
