Multiple giant eruptions and X-ray emission in the recoiling AGN/LBV candidate SDSS1133

TL;DR

This study analyzes 20 years of data on SDSS1133, revealing multiple eruptions and X-ray emission, supporting its classification as a luminous blue variable star with episodic giant eruptions, rather than a recoiling AGN.

Contribution

It provides the first comprehensive multi-wavelength analysis of SDSS1133, demonstrating its nature as an LBV with multiple eruptions and challenging previous AGN interpretations.

Findings

SDSS1133 experienced four major outbursts between 2001 and 2021.

Optical spectra show persistent broad hydrogen lines with high-velocity ejecta.

X-ray emission detected suggests interaction of ejected shells with circumstellar medium.

Abstract

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 four outbursts in 2001, 2014, 2019, and 2021. 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. {\it 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 suggests that SDSS1133 is an extreme luminous blue variable (LBV) star experiencing multiple giant eruptions with interactions of the ejected shell with different shells and/or circumstellar medium (CSM), and 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 or collapse to a massive black hole in future observations.