Probing the Jets of Blazars Using the Temporal Symmetry of Their
  Multi-Wavelength Outbursts
  We compare the rise and decay timescales of $\sim$200 long-term
($\sim$weeks-months) GeV and R-band outbursts and $\sim$25 short-term
($\sim$hr-day) GeV flares in a sample of 10 blazars using light curves from the
Fermi-LAT and the Yale/SMARTS monitoring project. We find that most of the
long-term outbursts are symmetric, indicating that the observed variability is
dominated by the crossing timescale of a disturbance, e.g., a shock. A larger
fraction of short-term flares are asymmetric with an approximately equal
fraction of longer and shorter decay than rise timescale. We employ the
MUlti-ZOne Radiation Feedback (MUZORF) model to interpret the above results. We
find that the outbursts with slow rise times indicate a gradual acceleration of
the particles to GeV energy. A change in the bulk Lorentz factor of the plasma
or the width of the shocked region can lead to an increase of the cooling time
causing a faster rise than decay time. Parameters such as the luminosity or the
distance of the broad line region (BLR) affects the cooling time strongly if a
single emission mechanism, e.g., external Compton scattering of BLR photons is
considered but may not if other mechanisms, e.g., synchrotron self-compton and
external Compton scattering of the torus photon are included. This work carries
out a systematic study of the symmetry of flares, which can be used to estimate
relevant geometric and physical parameters of blazar jets in the context of the
MUZORF model.
