TY - JOUR
TI - Circumnuclear Dust in AP Librae and the Source of Its VHE Emission
AU - Roychowdhury, Agniva
AU - Meyer, Eileen T.
AU - Georganopoulos, Markos and
AU - Breiding, Peter
AU - Petropoulou, Maria
JO - ASTROPHYSICAL JOURNAL
PY - 2022
VL - 924
TODO - 2
SP - null
PB - IOP Publishing Ltd
SN - 0004-637X
TODO - 10.3847/1538-4357/ac34f1
TODO - null
TODO - The broad high-energy spectral component in blazars is usually
attributed to various inverse Compton scattering processes in the
relativistic jet, but has not been clearly identified in most cases due
to degeneracies in physical models. AP Librae, a low-synchrotron-peaking
BL Lac object (LBL) detected in 2015 by H.E.S.S. at very high energies
(VHE; >0.5 TeV), has an extremely broad high-energy spectrum, covering
similar to 9 decades in energy. Standard synchrotron self-Compton models
generally fail to reproduce the VHE emission, which has led to the
suggestion that it might arise not from the blazar core, but on
kiloparsec scales from inverse Compton (IC) scattering of cosmic
microwave background (CMB) photons by a still-relativistic jet (IC/CMB).
IC/CMB models for the TeV emission of AP Librae in prior works have
implied a high level of infrared emission from the kiloparsec-scale jet.
With newly obtained Hubble Space Telescope (HST) imaging, we obtain a
deep upper limit on the kiloparsec-scale jet emission at 1.6 mu m, well
below the expected level. High-resolution Atacama Large
Millimeter/submillimeter Array imaging in bands 3-9 reveals a residual
dust-disk signature after core subtraction, with a clearly thermal
spectrum, and an extent (similar to 500 pc) that matches with a nonjet
residual emission seen after point-spread function subtraction in our
1.6 mu m HST imaging. We find that the unusually broad GeV and VHE
emission in AP Librae can be reproduced through the combined IC
scattering of photons from the CMB and the dust disk, respectively, by
electrons in both the blazar core and subkiloparsec jet.
ER -