* Astronomy

Title: The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
Authors: N. Tominaga, M. Limongi, T. Suzuki, M. Tanaka, K. Nomoto, K. Maeda, A. Chieffi, A. Tornambe, T. Minezaki, Y. Yoshii, I. Sakon, T. Wada, Y. Ohyama, T. Tanabé, H. Kaneda, T. Onaka, T. Nozawa, T. Kozasa, K. S. Kawabata, G. C. Anupama, D.K. Sahu, U.K. Gurugubelli, T.P. Prabhu, J. Deng
(Version v3)

We present a theoretical model for Type Ib supernova (SN) 2006jc. We calculate the evolution of the progenitor star, hydrodynamics and nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC). The synthetic bolometric LC is compared with the observed bolometric LC constructed by integrating the UV, optical, near-infrared (NIR), and mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as 40 solar masses on the zero-age main-sequence. The star undergoes extensive mass loss to reduce its mass down to as small as 6.9 solar masses, thus becoming a WCO Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which amorphous carbon grains can be formed. This could explain the NIR brightening and the dust feature seen in the MIR spectrum. We suggest that the progenitor of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and such massive stars are the important sites of dust formation. We derive the parameters of the explosion model in order to reproduce the bolometric LC of SN 2006jc by the radioactive decays: the ejecta mass 4.9 solar masses, hypernova-like explosion energy 10^{52} ergs, and ejected ^{56}$Ni mass 0.22 solar masses. We also calculate the circumstellar interaction and find that a CSM with a flat density structure is required to reproduce the X-ray LC of SN 2006jc. This suggests a drastic change of the mass-loss rate and/or the wind velocity that is consistent with the past luminous blue variable (LBV)-like event.

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Title: Properties of newly formed dust by SN2006jc based on near-to-mid infrared observation with AKARI
Authors: I. Sakon, T. Wada, Y. Ohyama, D. Ishihara, T. Tanabé, H. Kaneda, T. Onaka, N. Tominaga, M. Tanaka, T. Suzuki, H. Umeda, K. Nomoto, T. Nozawa, T. Kozasa, T. Minezaki, Y. Yoshii, S. Ohyabu, F. Usui, H. Matsuhara, T. Nakagawa, H. Murakami

We present our latest results on near- to mid- infrared observation of SN2006jc at 200 days after the discovery using the Infrared Camera (IRC) on board AKARI. The near-infrared (2--5 \mu m) spectrum of SN2006jc is obtained for the first time and is found to be well interpreted in terms of the thermal emission from amorphous carbon of 800 ± 10K with the mass of 6.9 ± 0.5 x 10^{-5}M_{\odot} that was formed in the supernova ejecta. This dust mass newly formed in the ejecta of SN 2006jc is in a range similar to those obtained for other several dust forming core collapse supernovae based on recent observations (i.e., 10^{-3}--10^{-5} M_{\odot}). Mid-infrared photometric data with {AKARI} /IRC MIR-S/S7, S9W, and S11 bands have shown excess emission over the thermal emission by hot amorphous carbon of 800K. This mid-infrared excess emission is likely to be accounted for by the emission from warm amorphous carbon dust of 320 ± 10K with the mass of 2.7^{+0.7}_{-0.5} x 10^{-3}M_{\odot} rather than by the band emission of astronomical silicate and/or silica grains. This warm amorphous carbon dust is expected to have been formed in the mass loss wind associated with the Wolf-Rayet stellar activity before the SN explosion. Our result suggests that a significant amount of dust is condensed in the mass loss wind prior to the SN explosion. A possible contribution of emission bands by precursory SiO molecules in 7.5--9.5 \mu m is also suggested.

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Two explosions observed in 2004 and 2006 in a galaxy 78 million light years from Earth were part of the fiery death of one of the most massive stars known to exist, astronomers said on Wednesday.
Writing in the journal Nature, the scientists described the supernova death of a star estimated to be 50 to 100 times as massive as our sun in a galaxy called UGC4904 in the Lynx constellation. A supernova is a gigantic explosion that marks the demise of a star.
The researchers said Japanese astronomer Koichi Itagaki discovered a faint celestial explosion that remained visible for about 10 days in 2004, then detected a second, much more powerful explosion two years later.

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Title: A giant outburst two years before the core- collapse of a massive star
Authors: A. Pastorello, S.J. Smartt, S. Mattila, J.J. Eldridge, D. Young, K. Itagaki, H. Yamaoka, H. Navasardyan, S. Valenti, F. Patat, I. Agnoletto, T. Augusteijn, S. Benetti, E. Cappellaro, T. Boles, J.- M. Bonnet- Bidaud, M.T. Botticella, F. Bufano, C. Cao, J. Deng, M. Dennefeld,  N. Elias- Rosa,  A. Harutyunyan, F.P. Keenan, T. Iijima, V. Lorenzi, P.A. Mazzali, X. Meng, S. Nakano, T.B. Nielsen, J.V. Smoker, V. Stanishev, M. Turatto, D. Xu, L. Zampieri

The death of massive stars produces a variety of supernovae, which are linked to the structure of the exploding stars 1,2 . The detection of several precursor stars of Type II supernovae have been reported (e.g. Ref. 3), however we do not yet have direct information on the progenitors of the hydrogen deficient Type Ib and Ic supernovae. Here we report that the peculiar Type Ib supernova SN2006jc is spatially coincident with a bright optical transient 4 that occurred in 2004. Spectroscopic and photometric monitoring of the supernova leads us to suggest that the progenitor was a carbon- oxygen Wolf- Rayet star embedded within a helium- rich circumstellar medium. There are different possible explanations for this pre- explosion transient. It appears similar to the giant outbursts of Luminous Blue Variables (LBV) of 60- 100 solar mass (M) stars 5 , however the progenitor of SN2006jc was helium and hydrogen deficient. An LBV-like outburst of a Wolf- Rayet star could be invoked, but this would be the first observational evidence of such a phenomenon. Alternatively a massive binary system composed of an LBV which erupted in 2004, and a Wolf- Rayet star exploding as SN2006jc, could explain the observations.

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