* Astronomy

Blobrana · L

RE: Supernova 2006gy

Blobrana · L

Title: SN 2006gy: An extremely luminous supernova in the galaxy NGC 1260
Authors: E. O. Ofek, P. B. Cameron, M. M. Kasliwal, A. Gal-Yam, A. Rau, S. R. Kulkarni, D. A. Frail, P. Chandra, S. B. Cenko, A. M. Soderberg, S. Immler
(revised v2)

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 multi-wavelength observations of this SN and its environment. Our spectroscopy shows an H alpha emission line as well as absorption features which may be identified as SiII lines at low expansion velocity. The high peak luminosity, the slow rise to maximum, and the narrow H alpha line are similar to those observed in hybrid type-Ia/IIn (also called IIa) SNe. 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 HII region in the vicinity of the SN. The extra-ordinarily large peak luminosity, ~3x10^44 erg/s, demands a dense circum-stellar medium, regardless of the mass of the progenitor star. The inferred mass loss rate of the progenitor is ~0.1 solar mass per year 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 two months is about 1.1x10^51 erg, which is only a factor of two less than that available from a super-Chandrasekhar 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 (e.g., pair production SN).

Read more (239kb, PDF)

-- Edited by Blobrana at 14:59, 2007-05-08

Blobrana · L

A supernova intrinsically two to three times brighter than any previously recorded has been observed, and its characteristics suggest it did not form like others of its class.
It appears to have been forged in a collision between two stars, adding fuel to a long-running debate about what causes the type Ia explosions that are a crucial tool in cosmology.
The prevailing view of type Ia supernovae is that they result from a dense stellar corpse called a white dwarf that slowly collects matter from an ordinary companion star. Eventually the white dwarf reaches a mass threshold called the Chandrasekhar limit, triggering an explosion that completely destroys it.
This mass cut-off is thought to make all such supernovae explode with about the same intrinsic brightness, allowing astronomers to calculate their distance based on how bright they appear through telescopes. In fact, it was observations of type Ia supernovae that led to the surprising discovery in 1998 that some mysterious entity, dubbed dark energy, was causing the universe's expansion to speed up.
But some astronomers have argued that type Ia's are actually due to two white dwarfs merging. The combined mass of the two objects is above the Chandrasekhar limit, leading to the explosion.

Evidence for this hypothesis came in 2002 from a supernova called 2002ic. It had some characteristics of type Ia's, but unlike others of its type, it also showed clear signs of hydrogen in its light spectrum. Some researchers said that could be explained by a white dwarf colliding with the core of a red giant star – a dying, Sun-like star that bloats up and starts expelling its outer layers before becoming a white dwarf itself.

The brightest supernova ever seen appears as a dark spot (arrow) in this negative infrared image taken by the Palomar 5-metre telescope. The other dark spot at centre is the host galaxy’s core
Image: E Ofek et al/Caltech/Palomar Observatory

Read more

Blobrana · L

Title: The brightest supernova ever recorded, powered by the death of an extremely massive star
Authors: Nathan Smith, Weidong Li, Ryan J. Foley, Ryan Chornock, Alexei V. Filippenko, David Pooley, Robert Quimby, J. Craig Wheeler, Joshua S. Bloom, Charles Hansen

Supernovae resulting from the deaths of massive stars span a wide range of peak luminosities, usually reached within 30 days after explosion. Their diversity depends on the star's initial mass and rate of mass loss during its lifetime. Stars born with initial masses above 40 times the mass of the Sun are expected to shed their hydrogen envelopes to expose their He core before they die, resulting in supernovae with little or no evidence for hydrogen gas observed in their spectrum. Here we report on our discovery and follow-up observations of SN 2006gy, which reveal that it reached a peak luminosity at least 3 times greater than any other supernova seen to date, and far greater than most others. We find that a large ejected mass of order 100 Solar masses is required to power its enormous total radiated luminosity, indicating a total kinetic energy of more than 10^52 ergs. This suggests that SN 2006gy marked the demise of an extremely massive star that, contrary to expectations, failed to shed its massive hydrogen envelope. A circumstellar shell that surrounded the progenitor star has a large mass and expansion speed, effectively ruling-out certain types of progenitor stars. Based on a number of lines of evidence, we suggest that the progenitor was a very massive evolved object like eta Carinae, which is the most luminous star known in the Milky Way. These observations suggest that the most massive stars can explode earlier than expected, and can create bright supernovae instead of dying ignominious deaths through direct collapse to a black hole. If such a fate is common, then supernovae from the first stars in the universe, which may have been extremely massive, will be more numerous than previously believed.

Read more (889kb, PDF)

The magnitude 14.9, type II supernova 2006gy, was discovered on the 18th September, 2006, by the Texas Supernova Search, in the spiral galaxy NGC 1260.
The supernova was located 2".0 west and 0".4 north of the centre of NGC 1260.

Position(2000): R.A. = 03h17m27s.06, Dec. = +41°24'19".5

Blobrana · L

NGC1260

Blobrana · L

Supernova 2006gy