Gaia17biu/SN 2017egm in NGC 3191: The Closest Hydrogen-poor Superluminous Supernova to Date Is in a "Normal," Massive, Metal-rich Spiral Galaxy

• Published in: The Astrophysical journal Vol. 853; no. 1; pp. 57 - 76
• Main Authors: Bose, Subhash, Dong, Subo, Pastorello, A., Filippenko, Alexei V., Kochanek, C. S., Mauerhan, Jon, Romero-Cañizales, C., Brink, Thomas G., Chen, Ping, Prieto, J. L., Post, R., Ashall, Christopher, Grupe, Dirk, Tomasella, L., Benetti, Stefano, Shappee, B. J., Stanek, K. Z., Cai, Zheng, Falco, E., Lundqvist, Peter, Mattila, Seppo, Mutel, Robert, Ochner, Paolo, Pooley, David, Stritzinger, M. D., Villanueva, S., Zheng, WeiKang, Beswick, R. J., Brown, Peter J., Cappellaro, E., Davis, Scott, Fraser, Morgan, Jaeger, Thomas de, Elias-Rosa, N., Gall, C., Gaudi, B. Scott, Herczeg, Gregory J., Hestenes, Julia, Holoien, T. W.-S., Hosseinzadeh, Griffin, Hsiao, E. Y., Hu, Shaoming, Jaejin, Shin, Jeffers, Ben, Koff, R. A., Kumar, Sahana, Kurtenkov, Alexander, Lau, Marie Wingyee, Prentice, Simon, Reynolds, T., Rudy, Richard J., Shahbandeh, Melissa, Somero, Auni, Stassun, Keivan G., Thompson, Todd A., Valenti, Stefano, Woo, Jong-Hak, Yunus, Sameen
• Format: Journal Article
• Language: English
• Published: Philadelphia The American Astronomical Society 20.01.2018; IOP Publishing; Institute of Physics (IOP)
• Subjects: ASTRONOMY AND ASTROPHYSICS; Astrophysics; Dwarf galaxies; Explosions; galaxies: individual (NGC 3191); Gamma ray bursts; Gamma rays; Hydrogen; Luminosity; Metallicity; Radio astronomy; Red shift; Spiral galaxies; Star formation; Stars & galaxies; Stellar mass; Supernova; Supernovae; supernovae: general; supernovae: individual (SN 2017egm, Gaia17biu)
• ISSN: 0004-637X; 1538-4357; 1538-4357
• DOI: 10.3847/1538-4357/aaa298

Hydrogen-poor superluminous supernovae (SLSNe-I) have been predominantly found in low-metallicity, star-forming dwarf galaxies. Here we identify Gaia17biu/SN 2017egm as an SLSN-I occurring in a "normal" spiral galaxy (NGC 3191) in terms of stellar mass (several times 1010 M ) and metallicity (roughly solar). At redshift z = 0.031, Gaia17biu is also the lowest-redshift SLSN-I to date, and the absence of a larger population of SLSNe-I in dwarf galaxies of similar redshift suggests that metallicity is likely less important to the production of SLSNe-I than previously believed. With the smallest distance and highest apparent brightness for an SLSN-I, we are able to study Gaia17biu in unprecedented detail. Its pre-peak near-ultraviolet to optical color is similar to that of Gaia16apd and among the bluest observed for an SLSN-I, while its peak luminosity (Mg = −21 mag) is substantially lower than that of Gaia16apd. Thanks to the high signal-to-noise ratios of our spectra, we identify several new spectroscopic features that may help to probe the properties of these enigmatic explosions. We detect polarization at the ∼0.5% level that is not strongly dependent on wavelength, suggesting a modest, global departure from spherical symmetry. In addition, we put the tightest upper limit yet on the radio luminosity of an SLSN-I with <5.4 × 1026 erg s−1 Hz−1 at 10 GHz, which is almost a factor of 40 better than previous upper limits and one of the few measured at an early stage in the evolution of an SLSN-I. This limit largely rules out an association of this SLSN-I with known populations of gamma-ray-burst-like central engines.