SN 2006gy Research Articles

SN 2006gy: WAS IT REALLY EXTRAORDINARY?

We present an optical photometric and spectroscopic study of the very luminous type IIn SN 2006gy for a time period spanning more than one year. In photometry, a broad, bright (M_R~-21.7) peak characterizes all BVRI light curves. Afterwards, a rapid luminosity fading is followed by a phase of slow luminosity decline between day ~170 and ~237. At late phases (>237 days), because of the large luminosity drop (>3 mag), only upper visibility limits are obtained in the B, R and I bands. In the near-infrared, two K-band detections on days 411 and 510 open new issues about dust formation or IR echoes scenarios. At all epochs the spectra are characterized by the absence of broad P-Cygni profiles and a multicomponent Halpha profile, which are the typical signatures of type IIn SNe. After maximum, spectroscopic and photometric similarities are found between SN 2006gy and bright, interaction-dominated SNe (e.g. SN 1997cy, SN 1999E and SN 2002ic). This suggests that ejecta-CSM interaction plays a key role in SN 2006gy about 6 to 8 months after maximum, sustaining the late-time-light curve. Alternatively, the late luminosity may be related to the radioactive decay of ~3M_sun of 56Ni. Models of the light curve in the first 170 days suggest that the progenitor was a compact star (R~6-8 10^(12)cm, M_ej~5-14M_sun), and that the SN ejecta collided with massive (6-10M_sun), opaque clumps of previously ejected material. These clumps do not completely obscure the SN photosphere, so that at its peak the luminosity is due both to the decay of 56Ni and to interaction with CSM. A supermassive star is not required to explain the observational data, nor is an extra-ordinarily large explosion energy.

TeV Gamma-Ray Metagalactic Sources at the Distance Range fromz= 0.0179 to 1.375: Spectral Energy Distributions and Images

Exploration of the galactic and metagalactic objects in which the acceleration of protons and nuclei is accompanying with generation of gamma-quanta and neutrinos is of great current interest for astroparticle physics. These gamma-astronomical researches are carrying out with SHALON mirror telescope at the Tien-Shan high-mountain observatory. The observation results of of metagalactic sources which are active galactic nuclei: FSRQs 3c454.3, 1739+522 and BLLacs Mkn 421, Mkn 501, Seyfert galaxy NGC 1275 and extragalactic Supernova SN2006 gy are presented. NGC 1275 is being intensively studied with SHALON since 1996. The flux increase was detected from the region NGC 1275 in autumn 2006. The detailed analysis of gamma-shower direction turned out the detection of metagalactic object. This object was identified with the supernova SN 2006gy that is about 10 minutes away from NGC 1275. So, the explosion of extragalactic supernova was observed at TeV energies for the first time with SHALON Cherenkov telescope. Th...

The Most Massive Core‐Collapse Supernova Progenitors

The discovery of the extremely luminous supernova SN 2006gy, possibly interpreted as a pair instability supernova, renewed the interest in very massive stars. We explore the evolution of these objects, which end their life as pair instability supernovae or as core collapse supernovae with relatively massive iron cores, up to about $3 M_\odot$.

Around the Pair Instability Valley – Massive SN Progenitors

AbstractThe discovery of the extremely luminous supernova SN 2006gy, possibly interpreted as a pair instability supernova, renewed the interest in very massive stars. We explore the evolution of these objects, which end their life as pair instability supernovae or as core collapse supernovae with relatively massive iron cores, up to about 3 M⊙.

How Much56Ni Can Be Produced in Core‐Collapse Supernovae? Evolution and Explosions of 30–100M⊙Stars

Motivated by the discovery of extremely bright supernovae SNe 1999as and 2006gy, we have investigated how much 56Ni mass can be synthesized in core-collapse massive supernovae (SNe). We calculate the evolution of several very massive stars with initial masses M ≤ 100 M☉ from the main sequence to the beginning of the Fe core collapse and simulate their explosions and nucleosynthesis. In order to avoid complications associated with strong mass loss, we consider only metal-poor stars with initial metallicity Z = Z☉/200. However, our results are applicable to higher metallicity models with similar C+O core masses. The C+O core mass for the 100 M☉ model is MCO = 42.6 M☉, and this is the heaviest model in the literature for which Fe-core-collapse SN is explored. The synthesized 56Ni mass increases with the increasing explosion energy and progenitor mass. For the explosion energy of E51 ≡ E/1051 ergs = 30, for example, the 56Ni masses of M(56Ni) = 2.2, 2.3, 5.0, and 6.6 M☉ can be produced for the progenitors with initial masses of 30, 50, 80, and 100 M☉ (or C+O core masses MCO = 11.4, 19.3, 34.0, and 42.6 M☉), respectively. We find that producing M(56Ni) ~ 4 M☉ as seen in SN 1999as is possible for MCO 34 M☉ and E51 20. Producing M(56Ni) ~ 13 M☉, as suggested for SN 2006gy, requires a too large explosion energy for MCO 43 M☉, but it may be possible with a reasonable explosion energy if MCO 60 M☉.

Pulsational pair instability as an explanation for the most luminous supernovae

The extremely luminous supernova SN 2006gy (ref. 1) challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too luminous by more than a factor of ten. Here we report that the brightest supernovae in the modern Universe arise from collisions between shells of matter ejected by massive stars that undergo an interior instability arising from the production of electron-positron pairs. This 'pair instability' leads to explosive burning that is insufficient to unbind the star, but ejects many solar masses of the envelope. After the first explosion, the remaining core contracts and searches for a stable burning state. When the next explosion occurs, several solar masses of material are again ejected, which collide with the earlier ejecta. This collision can radiate 10(50) erg of light, about a factor of ten more than an ordinary supernova. Our model is in good agreement with the observed light curve for SN 2006gy and also shows that some massive stars can produce more than one supernova-like outburst.

A runaway collision in a young star cluster as the origin of the brightest supernova

Supernova SN 2006gy in the galaxy NGC 1260 is the most luminous recorded. Its progenitor might have been a very massive (>100 Mo, where is the mass of the Sun) star, but that interpretation is incompatible with hydrogen in the spectrum of the supernova; stars >40 Moare believed to have shed their hydrogen envelopes several hundred thousand years before the explosion. Alternatively, the progenitor might have arisen from the merger of two massive stars. Here we show that the collision frequency of massive stars in a dense and young cluster (of the kind to be expected near the centre of a galaxy) is sufficient to provide a reasonable chance that SN 2006gy resulted from such a bombardment. If this is the correct explanation, then we predict that when the supernova fades (in a year or so) a dense cluster of massive stars will become visible at the site of the explosion.

Shell-shocked Diffusion Model for the Light Curve of SN 2006gy

We explore a simple model for the high luminosity of SN 2006gy involving photon diffusion of shock-deposited thermal energy. The distinguishing property of the model is that the large “stellar” radius of ∼160 AU required to prevent adiabatic losses is not the true stellar radius, but rather, it is the radius of an opaque, unbound circumstellar envelope, created when ∼10 M, was ejected in the decade before the supernova in an eruption analogous to that of h Carinae. The supernova light is produced primarily by diffusion of thermal energy following the passage of the blast wave through this shell. This model differs from traditional models of supernova debris interacting with an external circumstellar medium (CSM) in that here the shell is optically thick and the escape of radiation is delayed. We show that any model attempting to account for SN 2006gy’s huge luminosity with radiation emitted by ongoing CSM interaction fails for the following basic reason: the CSM density required to achieve the observed luminosity makes the same circumstellar envelope opaque ( ), forcing a thermal t 300 diffusion solution. In our model, the weaker CSM interaction giving rise to SN 2006gy’s characteristic Type IIn spectrum and soft X-rays is not linked to the power source of the visual continuum; instead, it arises after the blast wave breaks free from the opaque shell into the surrounding wind. While a simple diffusion model can explain the gross properties of the early light curve of SN 2006gy, it predicts that the light curve must plummet rapidly at late times, unless an additional power source is present. Subject headings: circumstellar matter — stars: evolution — supernovae: individual (SN 2006gy)

SN 2005ap: A Most Brilliant Explosion

We present unfiltered photometric observations with ROTSE-III and optical spectroscopic follow-up with HET and the Keck telescope of the most luminous supernova yet identified, SN 2005ap. The spectra taken about 3 days before and 6 days after maximum light show narrow emission lines (likely originating in the dwarf host) and absorption lines at a redshift of z = 0.2832, which puts the peak unfiltered magnitude at -22.7 ± 0.1 absolute. Broad P Cygni features corresponding to Hα, C III, N III, and O III are further detected with a photospheric velocity of ~20,000 km s-1. Unlike other highly luminous supernovae such as 2006gy and 2006tf that show slow photometric evolution, the light curve of SN 2005ap indicates a 1-3 week rise to peak followed by a relatively rapid decay. The spectra also lack the distinct emission peaks from moderately broadened (FWHM ~2000 km s-1) Balmer lines seen in SN 2006gy and SN 2006tf. We briefly discuss the origin of the extraordinary luminosity from a strong interaction as may be expected from a pair instability eruption or a GRB-like engine encased in a H/He envelope.

Pair creation supernovae at low and high redshift

Aims. Pair creation supernovae (PCSN) are thought to be produced from very massive low metallicity stars. The spectacularly bright SN 2006gy does show several signatures expected from PCSNe. Here, we investigate the metallicity threshold below which PCSN can form and estimate their occurrence rate. Methods. We perform stellar evolution calculations for stars of 150 Mand 250 Mof low metallicity (Z� / 5a ndZ� /20), and analyze their mass loss rates. Results. We find that the bifurcation between quasi-chemically homogeneous evolution for fast rotation and conventional evolu- tion for slower rotation, which has been found earlier for massive low metallicity stars, persists in the mass range considered here. Consequently, there are two separate PCSN progenitor types: (I) fast rotators produce PCSNe from very massive Wolf-Rayet stars, and (II) slower rotators that generate PCSNe in hydrogen-rich massive yellow hypergiants. Conclusions. We find that hydrogen-rich PCSNe could occur at metallicities as high as Z� /3, which - assuming standard IMFs are still valid to estimate their birth rates - results in a rate of about one PCSN per 1000 supernovae in the local universe, and one PCSN per 100 supernovae at a redshift of z = 5. PCSNe from WC-type Wolf-Rayet stars are restricted to much lower metallicity.

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

(abridged) We report our discovery and observations of the peculiar Type IIn supernova SN2006gy in NGC1260, revealing that it reached a peak magnitude of -22, making it the most luminous supernova ever recorded. It is not yet clear what powers the total radiated energy of 1e51 erg, but we argue that any mechanism -- thermal emission, circumstellar interaction, or 56Ni decay -- requires a very massive progenitor star. The circumstellar interaction hypothesis would require truly exceptional conditions around the star probably experienced an LBV eruption like the 19th century eruption of eta Carinae. Alternatively, radioactive decay of 56Ni may be a less objectionable hypothesis. That power source would imply a large Ni mass of 22 Msun, requiring that SN2006gy was a pair-instability supernova where the star's core was obliterated. SN2006gy 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 rule out the hypothesis that SN 2006gy was a ``Type IIa'' event. Instead, we propose that the progenitor may have been a very massive evolved object like eta Carinae that, contrary to expectations, failed to completely shed its massive hydrogen envelope before it died. Our interpretation of SN2006gy implies that the most massive stars can explode earlier than expected, during the LBV phase, preventing them from ever becoming Wolf-Rayet stars. SN2006gy also suggests that the most massive stars can create brilliant supernovae instead of dying ignominious deaths through direct collapse to a black hole.

SN 2006gy: An Extremely Luminous Supernova in the Galaxy NGC 1260

With an extinction-corrected V-band peak absolute magnitude of about -22, supernova SN 2006gy is probably the brightest SN ever observed. We report on multiwavelength observations of this SN and its environment. Our spectroscopy shows an Hα emission line as well as absorption features that may be identified as Si II lines at low expansion velocity. The slow brightening, the peak luminosity, and the Hα emission line resemble those observed in hybrid Type IIn/Ia SNe (also known as Type IIa) and may suggest that SN 2006gy is related to the Type IIa SNe class. The host galaxy, NGC 1260, is dominated by an old stellar population with solar metallicity. However, our high-resolution adaptive optics images reveal a dust lane in this galaxy, and there appears to be an H II region in the vicinity of the SN. The extraordinarily large peak luminosity, ~3 × 10^(44) ergs s^(-1), demands a dense circumstellar medium, regardless of the mass of the progenitor star. The inferred mass-loss rate of the progenitor is ~0.1 M_☉ yr^(-1) over a period of ~10 yr prior to explosion. Such an high mass-loss rate may be the result of a binary star common envelope ejection. The total radiated energy in the first 2 months is about 1.1 × 10^(51) ergs, which is only a factor of 2 less than that available from a super-Chandrasekhar Type Ia explosion. Therefore, given the presence of a star-forming region in the vicinity of the SN and the high-energy requirements, a plausible scenario is that SN 2006gy is related to the death of a massive star