Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV
  candidate SDSS1133
  We present a comprehensive analysis of 20 years worth of multi-color
photometric light curves, multi-epoch optical spectra, and X-ray data of an
off-nuclear variable object SDSS1133 in Mrk 177 at $z=0.0079$. The UV-optical
light curves reveal that SDSS1133 experienced three outbursts in 2001, 2014,
and 2019. The persistent UV-optical luminosity in the non-outbursting state is
$\sim 10^{41}$ erg/s with small-scale flux variations, and peak luminosities
during the outbursts reach $\sim 10^{42}$ erg/s. The optical spectra exhibit
enduring broad hydrogen Balmer P-Cygni profiles with the absorption minimum at
$\sim -2,000$ km/s, indicating the presence of fast moving ejecta. Chandra
detected weak X-ray emission at a 0.3-10 keV luminosity of $L_{X} = 4 \times
10^{38}$ erg/s after the 2019 outburst. These lines of evidence strongly
suggests that SDSS1133 is an extremely luminous blue variable (LBV) star
experiencing multiple giant eruptions with interactions of the ejected shell
with different shells and/or circumstellar medium (CSM), and strongly disfavors
the recoiling Active Galactic Nuclei (AGN) scenario suggested in the
literature. We suggest that pulsational pair-instability may provide a viable
explanation for the multiple energetic eruptions in SDSS1133. If the current
activity of SDSS1133 is a precursor of a supernova explosion, we may be able to
observe a few additional giant eruptions and then the terminal supernova
explosion in future observations.
