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[en] Recently a Type Ic supernova, SN 1998bw, was discovered coincident with a gamma-ray burst, GRB 980425. The supernova had unusual radio, optical, and spectroscopic properties. Among other things, it was especially bright for a Type Ic both optically and in the radio, and it rose quickly to maximum. We explore here models based upon helium stars in the range 9 - 14 Mcircle-dot and carbon-oxygen stars 6 - 11 Mcircle-dot, which experience unusually energetic explosions (kinetic energy 0.5 - 2.8x1052 ergs). Bolometric light curves and multiband photometry are calculated and compared favorably with observations. No spectroscopic data are available at this time, but both LTE and non-LTE spectra are calculated for the model that agrees best with the light curve, a carbon-oxygen core of 6 Mcircle-dot exploded with a kinetic energy of 2.2x1052 ergs. We also examine potential mechanisms for producing the observed gamma-ray burst (GRB) shock breakout and relativistic shock deceleration in circumstellar material. For spherically symmetric models, both fail to produce a GRB of even the low luminosity inferred for GRB 980425. However, the high explosion energies required to understand the supernova are in contrast to what is expected for such massive stars and indicate that a new sort of explosion may have been identified, possibly the consequence of a collapsar. Indeed a more likely explanation for what was seen is a highly asymmetric explosion in which the GRB was produced by mildly relativistic matter (Γ∼5) running into circumstellar matter along the line of sight to the Earth. The explosion itself was powered by black hole accretion and jets, but unlike 'ordinary' gamma-ray bursts, the jets were not of sufficient energy and duration to effectively reach large values of Γ. They may also not have been oriented in our direction. The ejected mass (but not the 56Ni mass) and explosion energy are then smaller. Other associations between luminous Type Ic supernovae and GRBs may exist and should be sought, but most Type Ib and Type Ic supernovae do not make GRBs. copyright copyright 1999. The American Astronomical Society
[en] Recently, Warm (keV scale) Dark Matter emerged impressively over CDM (Cold Dark Matter) as the leading Dark Matter candidate. In the context of this new Dark Matter situation, which implies novelties in the astrophysical, cosmological and keV particle physics context, this 16. Paris Colloquium 2012 is devoted to the LambdaWDM Standard Model of the Universe. The topics of the colloquium are as follows: -) observational and theoretical progress on the nature of dark matter: keV scale warm dark matter, -) large and small scale structure formation in agreement with observations at large scales and small galactic scales, and -) neutrinos in astrophysics and cosmology. This document gathers the slides of the presentations.
[en] We present optical and infrared observations of the unusual Type Ia supernova (SN) 2004eo. The light curves and spectra closely resemble those of the prototypical SN 1992A, and the luminosity at maximum (MB = -19.08) is close to the average for a Type Ia supernova (SN Ia). However, the ejected 56Ni mass derived by modelling the bolometric light curve (about 0.45M.) lies near the lower limit of the 56Ni mass distribution observed in normal SNe Ia. Accordingly, SN 2004eo shows a relatively rapid post-maximum decline in the light curve [Δm15(B)(true) = 1.46], small expansion velocities in the ejecta and a depth ratio Si II λ 5972/ Si II λ 6355 similar to that of SN 1992A. The physical properties of SN 2004eo cause it to fall very close to the boundary between the faint, low-velocity gradient and high-velocity gradient subgroups proposed by Benetti et al. Similar behaviour is seen in a few other SNe Ia. Thus, there may in fact exist a few SNe Ia with intermediate physical properties. (authors)