Type Ia Supernova Explosion Models

Because calibrated light curves of Type Ia supernovae have become a major tool to determine the local expansion rate of the Universe and also its geometrical structure, considerable attention has been given to models of these events over the past couple of years. There are good reasons to believe that perhaps most Type Ia supernovae are the explosions of white dwarfs that have approached the Chandrasekhar mass, M_ch ~ 1.39 M_sun, and are disrupted by thermonuclear fusion of carbon and oxygen. However, the mechanism whereby such accreting carbon-oxygen white dwarfs explode continues to be uncertain. Recent progress in modeling Type Ia supernovae as well as several of the still open questions are addressed in this review. Although the main emphasis will be on studies of the explosion mechanism itself and on the related physical processes, including the physics of turbulent nuclear combustion in degenerate stars, we also discuss observational constraints.Comment: 38 pages, 4 figures, Annual Review of Astronomy and Astrophysics, in pres

A newly discovered double–double candidate microquasar in NGC 300

International audienceWe present the discovery of a powerful candidate microquasar in NGC 300, associated with the S 10 optical nebula (previously classified as a supernova remnant). Chandra images show four discrete X-ray knots aligned in the plane of the sky over a length of ≈150 pc. The X-ray emission from the knots is well fitted with a thermal plasma model at a temperature of ≈0.6 keV and a combined 0.3–8 keV luminosity of ≈10^37 erg s^−1. The X-ray core, if present at all, does not stand out above the thermal emission of the knots: this suggests that the accreting compact object is either currently in a dim state or occulted from our view. We interpret the emission from the knots as the result of shocks from the interaction of a jet with the interstellar medium (possibly over different epochs of enhanced activity). Cooler shock-heated gas is likely the origin also of the optical bubble and lobes near the X-ray structure, detected in images from the Hubble Space Telescope and the Very Large Telescope. In the radio bands, we observed the region with the Australia Telescope Compact Array, and discovered an elongated radio nebula (about 170 × 55 pc in size) with its major axis aligned with the chain of Chandra sources. The radio nebula has an integrated 5.5 GHz radio luminosity of |${\approx }10^{34}\, \rm{erg\,s^{-1}}$| for a distance of 1.88 Mpc. The morphology, size, and luminosity of the extended X-ray, optical, and radio structure suggest that NGC 300-S 10 belongs to the same class of powerful (P_jet > 10^39 erg s^−1) microquasars as SS 433, Ho II X-1, and NGC 7793-S 26

Optical IFU spectroscopy of a bipolar microquasar jet in NGC 300

International audienceWe recently reported the discovery of a candidate jet-driving microquasar (S10) in the nearby spiral galaxy NGC 300. However, in the absence of kinematic information, we could not reliably determine the jet power or the dynamical age of the jet cavity. Here, we present optical Multi Unit Spectroscopic Explorer (MUSE) integral field unit (IFU) observations of S10, which reveal a bipolar line-emitting jet structure surrounding a continuum-emitting central source. The optical jet lobes of S10 have a total extent of ∼40 pc and a shock velocity of ∼150 km s^−1. Together with the jet kinematics, we exploit the MUSE coverage of the Balmer Hβ line to estimate the density of the surrounding matter and therefore compute the jet power to be P_jet ≈ 6.3 × 10^38 erg s^−1. An optical analysis of a microquasar jet bubble and a consequent robust derivation of the jet power have been possible only in a handful of similar sources. This study therefore adds valuable insight into microquasar jets, and demonstrates the power of optical integral field spectroscopy in identifying and analysing these objects