SN 2006gy: Discovery of the Most Luminous Supernova Ever Recorded, Powered by the Death of an Extremely Massive Star like η Carinae

Abstract

We report the discovery and early observations of the peculiar Type IIn supernova (SN) 2006gy in NGC 1260. With a peak visual magnitude of about À22, it is the most luminous supernova ever recorded. Its very slow rise to maximum took $70 days, and it stayed brighter than À21 mag for about 100 days. It is not yet clear what powers the enormous luminosity and the total radiated energy of $10 51 erg, but we argue that any known mechanism-thermal emission, circumstellar interaction, or 56 Ni decay-requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star, which, in the decades before its death, must have experienced a luminous blue variable (LBV) eruption like the 19th century eruption of Carinae. However, this scenario fails to explain the weak and unabsorbed soft X-rays detected by Chandra. Radioactive decay of 56 Ni may be a less objectionable hypothesis, but it would imply a large Ni mass of $22 M , requiring SN 2006gy to have been a pair-instability supernova where the star's core was obliterated. While this is still uncertain, SN 2006gy is the first supernova for which we have good reason to suspect a pair-instability explosion. Based on a number of lines of evidence, we eliminate the hypothesis that SN 2006gy was a ''Type IIa'' event, that is, a white dwarf exploding inside a hydrogen envelope. Instead, we propose that the progenitor was a very massive evolved object like Carinae that, contrary to expectations, failed to shed its hydrogen envelope. SN 2006gy implies that some of the most massive stars can explode prematurely during the LBV phase, never becoming Wolf-Rayet stars. SN 2006gy also suggests that they can create brilliant supernovae instead of experiencing ignominious deaths through direct collapse to a black hole. If such a fate is common among the most massive stars, then observable supernovae from Population III stars in the early universe will be more numerous than previously believed.

Understanding extreme quasar optical variability with CRTS – I. Major AGN flares

“…In contrast, SLSNe-II have been attributed to more luminous versions of Type IIn supernova, which themselves are believed to be due to the end stages of luminous blue variables (LBVs) with massive circumstellar matter (CSM) envelopes. Both types of SLSNe have been measured to emit more than 10 51 erg of energy (Smith et al 2007;Drake et al 2010;Quimby et al 2011;Rest et al 2011) and are thus within the range of almost all the flares shown here. Furthermore, examples of SLSNe have been discovered up to redshifts of z = 3.9 (Cooke et al 2012).…”

LINE IDENTIFICATIONS OF TYPE I SUPERNOVAE: ON THE DETECTION OF Si II FOR THESE HYDROGEN-POOR EVENTS

“…SLSNII show conspicuous signatures of hydrogen; however, the hydrogen feature is so far like that of SNIIn (Dessart et al 2015a), i.e., narrow emission signatures of hydrogen, e.g., SN2006gy (Smith et al 2007) and 2008am (Chatzopoulos et al 2011).…”

Spectrum formation in superluminous supernovae (Type I)

“…Some SLSNe clearly bear the sign of interaction with a hydrogen-rich circum-stellar medium (CSM; Smith et al 2007;Ofek et al 2007;Drake et al 2011;Benetti et al 2014). This masks the actual SN ejecta, making their nature unclear, although a link with massive stars is likely (e.g., Smith et al 2007;Agnoletto et al 2009).…”

“…This masks the actual SN ejecta, making their nature unclear, although a link with massive stars is likely (e.g., Smith et al 2007;Agnoletto et al 2009). SLSNe without the signatures of interaction with a Hrich CSM, ("H-poor SLSNe") are in turn divided into two rather vaguely defined groups.…”