The Changing Look Blazar B2 1420+32
  Blazars are active galactic nuclei with their relativistic jets pointing
toward the observer, with two major sub-classes, the flat spectrum radio
quasars and BL Lac objects. We present multi-wavelength photometric and
spectroscopic monitoring observations of the blazar, B2 1420+32, focusing on
its outbursts in 2018-2020. Multi-epoch spectra show that the blazar exhibited
large scale spectral variability in both its continuum and line emission,
accompanied by dramatic gamma-ray and optical variability by factors of up to
40 and 15, respectively, on week to month timescales. Over the last decade, the
gamma-ray and optical fluxes increased by factors of 1500 and 100,
respectively. B2 1420+32 was an FSRQ with broad emission lines in 1995.
Following a series of flares starting in 2018, it transitioned between BL Lac
and FSRQ states multiple times, with the emergence of a strong Fe pseudo
continuum. Two spectra also contain components that can be modeled as
single-temperature black bodies of 12,000 and 5,200 K. Such a collection of
"changing look" features has never been observed previously in a blazar. We
measure gamma-ray-optical and the inter-band optical lags implying emission
region separations of less than 800 and 130 gravitational radii respectively.
Since most emission line flux variations, except the Fe continuum, are within a
factor of 2-3, the transitions between FSRQ and BL Lac classifications are
mainly caused by the continuum variability. The large Fe continuum flux
increase suggests the occurrence of dust sublimation releasing more Fe ions in
the central engine and an energy transfer from the relativistic jet to
sub-relativistic emission components.
