Speaker
Description
The production site and process responsible for the highly variable
high-energy emission observed from blazar jets are still debated.
Gravitational lenses can be used as microscopes to investigate the
nature of such sources. We study the broad-band spectral properties and
the high-energy variability of the gravitationally-lensed blazar PKS
1830-211, for which radio observations have revealed two images, to put
constraints on the jet physics and the existence of a
gravitationally-induced time delay and magnification ratio between the
images. We utilize Swift/XRT, NuSTAR, and Fermi-LAT observations from
2016 and 2019 to compare periods of low activity and high activity in
PKS 1830-211. Short-timescale variability is elucidated with an unbinned
power spectrum analysis of time-tagged NuSTAR photon data. To study the
gravitationally-induced time delay in the gamma-ray light curve observed
with Fermi-LAT, we elaborate on existing methods and introduce new
approaches. We develop a metric optimization method yielding a delay of
22.4 ± 5.7 days consistent with the value obtained by our
auto-correlation approach, 21.96 ± 0.30 days, both of which being
constant over time; the image magnification ratio is more difficult to
estimate, and is subject to a two-fold ambiguity. When comparing the
2016 and 2019 datasets, the X-ray part of the SED, especially as seen by
NuSTAR, is remarkably constant in comparison to the dramatic change in
the gamma-rays. The X-ray and gamma-ray parts of the SED can be fitted
with a single component resulting from Comptonisation of infrared
emission from the dusty torus, with different gamma-ray states arising
solely due to a shift of the break in the electron energy distribution.
The detection of a consistent lag throughout the whole light curve
suggests that the the gamma-rays originate from a persistent location in
the jet.
