The Curious Case of PHL 293B: A Long-lived Transient in a Metal-poor Blue Compact Dwarf Galaxy

Colin J. Burke, Vivienne F. Baldassare, Xin Liu, Ryan J. Foley, Yue Shen, Antonella Palmese, Hengxiao Guo, Kenneth Herner, Tim M.C. Abbott, Michel Aguena, Sahar Allam, Santiago Avila, Emmanuel Bertin, David Brooks, Aurelio Carnero Rosell, Matias Carrasco Kind, Jorge Carretero, Luiz N. Da Costa, Juan De Vicente, Shantanu DesaiPeter Doel, Tim F. Eifler, Spencer Everett, Josh Frieman, Juan García-Bellido, Enrique Gaztanaga, Daniel Gruen, Robert A. Gruendl, Julia Gschwend, Gaston Gutierrez, Devon L. Hollowood, Klaus Honscheid, David J. James, Elisabeth Krause, Kyler Kuehn, Marcio A.G. Maia, Felipe Menanteau, Ramon Miquel, Francisco Paz-Chinchón, Andrés A. Plazas, Eusebio Sanchez, Basilio Santiago, Vic Scarpine, Santiago Serrano, Ignacio Sevilla-Noarbe, Mathew Smith, Marcelle Soares-Santos, Eric Suchyta, Molly E.C. Swanson, Gregory Tarle, Douglas L. Tucker, Tamas Norbert Varga, Alistair R. Walker

Research output: Contribution to journalArticlepeer-review

6 Scopus citations

Abstract

We report on small-amplitude optical variability and recent dissipation of the unusually persistent broad emission lines in the blue compact dwarf galaxy PHL 293B. The galaxy's unusual spectral features (P Cygni-like profiles with ∼800 km s-1 blueshifted absorption lines) have resulted in conflicting interpretations of the nature of this source in the literature. However, analysis of new Gemini spectroscopy reveals the broad emission has begun to fade after being persistent for over a decade prior. Precise difference imaging light curves constructed with the Sloan Digital Sky Survey and the Dark Energy Survey reveal small-amplitude optical variability of ∼0.1 mag in the g band offset by 100 21 pc from the brightest pixel of the host. The light curve is well-described by an active galactic nuclei (AGN)-like damped random walk process. However, we conclude that the origin of the optical variability and spectral features of PHL 293B is due to a long-lived stellar transient, likely a Type IIn supernova or nonterminal outburst, mimicking long-term AGN-like variability. This work highlights the challenges of discriminating between scenarios in such extreme environments, relevant to searches for AGNs in dwarf galaxies. This is the second long-lived transient discovered in a blue compact dwarf, after SDSS1133. Our result implies such long-lived stellar transients may be more common in metal-deficient galaxies. Systematic searches for low-level variability in dwarf galaxies will be possible with the upcoming Legacy Survey of Space and Time at the Vera C. Rubin Observatory.

Original languageEnglish (US)
Article numberL5
JournalAstrophysical Journal Letters
Volume894
Issue number1
DOIs
StatePublished - May 1 2020

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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