* Astronomy

Title: SN Hunt 248: a super-Eddington outburst from a massive cool hypergiant
Author: Jon C. Mauerhan, Schuyler D. Van Dyk, Melissa L Graham, WeiKang Zheng, Kelsey I. Clubb, Alexei V. Filippenko, Stefano Valenti, Peter J. Brown, Nathan Smith, D. Andrew Howell, Iair Arcavi

We present photometric and spectroscopic observations of SN Hunt 248, a new supernova (SN) impostor in NGC 5806, which experienced a multi-stage outburst in May-June 2014. The initial "2014a" brightening that led to this object's discovery began with an absolute magnitude of -12, at which point the source exhibited the characteristics of a cool dense outflow, having a spectrum dominated by P-Cygni lines of Fe II, H I, and Na I, as well as strong line blanketing from metals (at the blue end). After two weeks of slow incline, the source rapidly climbed and peaked near M=-15 mag after two more weeks. During this bright "2014b" phase the source radiated a total energy of ~10^49 ergs, while the spectrum became dominated by Balmer emission and a stronger blue continuum, similar in appearance to the SN impostor SN 1997bs. Archival images of the host galaxy from the Hubble Space Telescope between 1997 and 2005 have revealed a luminous and variable precursor star. Its location on the HR diagram is consistent with a massive cool hypergiant having an extremely dense wind and an Eddington ratio just below unity. At the onset of the recent 2014a brightening, however, the object became super-Eddington. The subsequent boost in luminosity during the 2014b phase is suspected to be the result of interaction between the outflow and circumstellar material. SN Hunt 248 provides the first case of a cool hypergiant undergoing a giant eruption reminiscent of outbursts from luminous blue variable (LBV) stars. This lends support to the hypothesis that some cool hypergiants, like Rho Cas, could be LBVs masquerading under a pseudo-photosphere created by their extremely dense winds. Moreover, SN Hunt 248 demonstrates that eruptions stemming from such stars can rival in peak luminosity the giant outbursts of much more massive systems like Eta Car.

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