Connecting the progenitors, pre-explosion variability and giant outbursts of luminous blue variables with Gaia16cfr

We present multi-epoch, multi-colour pre-outburst photometry and\npost-outburst light curves and spectra of the luminous blue variable (LBV)\noutburst Gaia16cfr discovered by the Gaia satellite on 1 December 2016. We\ndetect Gaia16cfr in 13 epochs of Hubble Space Telescope imaging spanning phases\nof 10 yr to 8 months before the outburst and in Spitzer Space Telescope imaging\n13 years before outburst. Pre-outburst optical photometry is consistent with an\n18 Msun F8 I star, although the star was likely reddened and closer to 30 Msun.\nThe pre-outburst source exhibited a significant near-infrared excess consistent\nwith a 120 AU shell with 4x10-6 Msun of dust. We infer that the source was\nenshrouded by an optically-thick and compact shell of circumstellar material\nfrom an LBV wind, which formed a pseudo-photosphere consistent with S Dor-like\nvariables in their "maximum" phase. Within a year of outburst, the source was\nhighly variable on 10-30 day timescales. The outburst light curve closely\nmatches that of the 2012 outburst of SN 2009ip, although the observed\nvelocities are significantly slower than in that event. In Halpha, the outburst\nhad an excess of blueshifted emission at late times centred around -1500 km/s,\nsimilar to that of double-peaked Type IIn supernovae and the LBV outburst SN\n2015bh. From the pre-outburst and post-outburst photometry, we infer that the\noutburst ejecta are evolving into a dense, highly structured circumstellar\nenvironment from precursor outbursts within years of the December 2016 event.\n