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

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 three outbursts in 2001, 2014, and 2019. The persistent UVoptical luminosity in the non-outbursting state is ∼ 10 41 erg s −1 with small-scale flux variations, and peak luminosities during the outbursts reach ∼ 10 42 erg s −1 . The optical spectra exhibit enduring broad hydrogen Balmer P-Cygni profiles with the absorption minimum at ∼ −2, 000 km s −1 , indicating the presence of fast moving ejecta. Chandra detected weak X-ray emission at a 0.3 − 10 keV luminosity of L X = 4 × 10 38 erg s −1 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.

Decade-long time-monitoring of candidate Luminous Blue Variable Stars in the two very metal-deficient compact dwarf galaxies DDO 68 and PHL 293B

“…The LBV in the relatively low-metallicity galaxy Mrk 177 = UGCA 239 at the post-merger stage, with 12 + logO/H = 8.58 and DL = 28.9 Mpc, has undergone multiple outbursts during the last 20 years (Kokubo 2021). The luminosity of the broad Hα component of Mrk 177 varies from a maximum of 10 40 erg s −1 during the strongest explosion to 10 39 erg s −1 during the next two strong explosions.…”

“…However, very strong broad emission (FWHM > 1000 km s −1 ) can also be present in the spectra of objects other than massive stars, such as Type IIn Supernovae (SNe) and Active Galactic Nuclei (AGNs). In these objects, the luminosities of the broad Hα component are larger and can reach values up to 10 40 -10 42 ergs s −1 (Izotov et al 2007;Sobral et al 2020;Kokubo 2021;Burke et al 2021).…”

“…Well-known prototypes of this category are η Carinae and P Cygni with luminosities ∼10 40 ergs s −1 (Lamers et al 1983;Davidson 1999). In some cases, the peak luminosity during the outbursts can reach ∼10 42 ergs s −1 (Kokubo 2021). Nearly all these known luminous LBVs are either in our Galaxy or in nearby galaxies.…”

Electromagnetic Counterparts to Massive Black Hole Mergers

“…In contrast, the variable object SDSS 1133 is well separated from a nearby dwarf galaxy and has exhibited stochastic variability over a > 60 year time baseline (Koss et al, 2014). Its spectral features are quite unusual for an AGN, though, so this object may instead be a rare luminous blue variable star exhibiting repeated, extreme, non-terminal outbursts (Koss et al, 2014;Burke et al, 2020;Kokubo, 2021;Ward et al, 2021).…”

Decade-long time-monitoring of candidate luminous blue variable stars in the two very metal-deficient star-forming galaxies DDO 68 and PHL 293B

“…Well-known prototypes of this category are η Carinae and P Cygni with luminosities ∼10 40 erg s −1 (Lamers, de Groot & Cassatella 1983 ;Davidson 1999 ). In some cases, the peak luminosity during the outbursts can reach ∼10 42 erg s −1 (Kokubo 2021 ). Nearly all these known luminous LBVs are either in our Galaxy or in nearby galaxies.…”