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TOPIC: Cassiopeia A
Blobrana


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Cassiopeia A Movie: A Remnant Evolves


This new movie of X-ray data from Chandra of the supernova remnant Cassiopeia A (Cas A) was made by combining observations taken in January 2000, February 2002, February 2004, and December 2007. In these images, the lowest-energy X-rays Chandra detects are shown in red, intermediate energies in green, and the highest energies in blue. Scientists have used the movie to measure the expansion velocity of the leading edge of the explosion's outer blast wave (shown in blue). The researchers find that the velocity is 11 million miles per hour, which is significantly slower than expected for an explosion with the energy estimated to have been released in Cas A.
This slower velocity is explained by a special type of energy loss by the blast wave. Electrons are accelerated to high energies as they travel backwards and forwards across the shock front produced by the blast wave. As the electrons travel around magnetic fields in the shock they lose energy by producing synchrotron emission and glowing in X-rays. Scientists think heavier particles like protons and ions are accelerated in the same way. The energy lost by these heavier particles can amount to a large fraction of the energy from the supernova explosion, resulting in a slower shock velocity. The accelerated protons and ions which escape from the remnant are known as "cosmic rays", and continually bombard the Earth's atmosphere. Supernova remnants are believed to be one of the main sources of cosmic rays.
The authors have constructed a model that combined the measured expansion velocity, as well as its observed size, with estimates of the explosion energy, the mass of the ejected material in Cas A and efficient particle acceleration. For everything to agree, about 35% of the energy of the Cas A supernova went into accelerating cosmic rays.

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Blobrana


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Time travel seems like stuff of science fiction, but in a sense, astronomers do it all the time. The night sky before us is a vista of time, as we look further and further back in the hundreds or thousands of years it takes starlight to reach our eyes. Another record of time is etched on the sky by way of "light echoes."
Sky and Telescope reports that astronomers have found away to examine the light from a supernova blast that erupted, and faded away, more than 400 years ago. The astronomer's time machine is his or her telescope, attached with a spectrograph that splits the light into its rainbow of colours and records the data the spectrum contains.

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Blobrana


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Supernova 1572
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Birth of the Tycho Brahe's 1572 supernova remnant



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Blobrana


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Supernova 1572
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A team of astronomers has managed to re-watch the explosion of a star that died more than 400 years ago by studying light that has bounced off distant clouds of interstellar dust. Their astronomical archaeology could provide clues about dark energy, a mysterious force that may be pushing the Universe apart.
Observations confirm that the supernova was of a variety known as 'type 1a'. These supernovae are created by the explosion of small, dense stars called white dwarfs.

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Blobrana


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Astronomy and palaeontology have something in common: we both look at old things, and try to figure out how they came to be.
In astronomy, sadly, we cannot hold the equivalent of an old bone in our hands. All we get is light from an object (barring the occasional meteorite). So we have to look very carefully to see whats what. Sometimes, we have to look outside the visible spectrum, too. Not only that, like any good detective we have to check the context the neighbourhood too.

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Blobrana


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Hot spots near the shattered remains of an exploded star are echoing the blast's first moments, say scientists using data from NASA's Spitzer Space Telescope.
Eli Dwek of NASA's Goddard Space Flight Center in Greenbelt, Md. and Richard Arendt of the University of Maryland, Baltimore County, say these echoes are powered by radiation from Cassiopeia A supernova shock wave that blew the star apart some 11,000 years ago.

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Blobrana


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Cassiopeia A Supernova
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Title: The Cassiopeia A Supernova was of Type IIB
Authors: Oliver Krause, Stephan M. Birkmann, Tomonori Usuda, Takashi Hattori, Miwa Goto, George H. Rieke, Karl A. Misselt

Cassiopeia A is one of the youngest supernova remnants known in the Milky Way and a unique laboratory for supernova physics. We present an optical spectrum of the Cassiopeia A supernova near maximum brightness, obtained from observations of a scattered light echo - more than three centuries after the direct light of the explosion swept past Earth. The spectrum shows that Cassiopeia A was a type IIb supernova and originated from the collapse of the helium core of a red supergiant that had lost most of its hydrogen envelope prior to exploding. Our finding concludes a longstanding debate on the Cassiopeia A progenitor and provides new insight into supernova physics by linking the properties of the explosion to the wealth of knowledge about its remnant.

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Blobrana


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A massive star exploded in our Galaxy more than 11 000 years ago. The event, now known as "Cassiopeia A supernova", could have been seen from Earth around 1680, but seemingly almost everybody in our planet missed the show. But now, an international scientific team has performed an impressive work of celestial archaeology: they have used the interstellar dust as a look-back mirror that allowed them to receive news from the past. Some light from that explosion was reflected by dust clouds placed at some distance from the dying star, and this reflection has been detected and analysed. This way, modern astronomy witnesses the cataclysmic display that our ancestors did not study, for some reason, in the 17th century.

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Blobrana


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Astronomers have unearthed secrets from the grave of a star that blasted apart in a supernova explosion long ago. By decoding ghostly echoes of light travelling away from the remains of a supernova called Cassiopeia A, the scientists have pieced together what the star looked like in life, and ultimately how it met its demise.
The discovery, made using primarily NASA's Spitzer Space Telescope and Japan's Subaru telescope on Mauna Kea in Hawaii, represents the first time astronomers have been able to resurrect the life history of a supernova remnant in our own galaxy.

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Tycho's Supernova Remnant
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Title: Suzaku Observations of Tycho's Supernova Remnant
Authors: T. Tamagawa, A. Hayato, S. Nakamura, Y. Terada, A. Bamba, J. S. Hiraga, J. P. Hughes, U. Hwang, J. Kataoka, K. Kinugasa, H. Kunieda, T. Tanaka, H. Tsunemi, M. Ueno, S. S. Holt, M. Kokubun, E. Miyata, A. Szymkowiak, T. Takahashi, K. Tamura, D. Ueno, K. Makishima

Tycho's supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26-29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with photon index of 2.7 and a thermal bremsstrahlung model with temperature of 4.7 keV. The former component can alternatively be modelled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K_alpha line (6.445 keV), we observe for the first time significant K_alpha line emission from the trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K_beta lines from Ca (4.56 keV) and Fe (7.11 keV) are also seen. The ionisation states of Cr and Mn, based on their line centroids, are estimated to be similar to that of Fe K_alpha (Fe XV or XVI).

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