Type Ia Supernovae: An Examination of Potential Progenitors and the Redshift Distribution

We examine the possibility that supernovae type Ia (SN Ia) are produced by white dwarfs accreting from Roche-lobe filling evolved companions, under the assumption that a strong optically thick stellar wind from accretor is able to stabilize the mass transfer. We show that if a mass transfer phase on a thermal timescale precedes a nuclear burning driven phase, then such systems (of which the supersoft X-ray sources are a subgroup) can account for about 10% of the inferred SN Ia rate. In addition, we examine the cosmic history of the supernova rate, and we show that the ratio of the rate of SN Ia to the rate of supernovae produced by massive stars (supernovae of types II, Ib, Ic) should increase from about z = 1 towards lower redshifts.Comment: 29 pages, Latex, 6 figures, aasms4.sty, psfig.sty, to appear in The Astrophysical Journa

The GRB luminosity function: predictions from the internal shock model and comparison with observations

International audienceWe compute the expected luminosity function of gamma-ray bursts (GRBs) in the context of the internal shock model. We assume that GRB central engines generate relativistic outflows characterized by the respective distributions of injected kinetic power and contrast in Lorentz factor κ = Γmax/Γmin. We find that if the distribution of contrast extends down to values close to unity (i.e. if both highly variable and smooth outflows can exist), then the luminosity function has two branches. At high luminosity it follows the distribution of while at low luminosity it is close to a power law of slope -0.5. We then examine if existing data can constrain the luminosity function. Using the logN-logP curve, the Ep distribution of bright Burst and Transient Source Experiment (BATSE) bursts and the X-ray flash (XRF)/GRB ratio obtained by High Energy Transient Explorer 2 (HETE2), we show that single and broken power laws can provide equally good fits of these data. Present observations are therefore unable to favour one form or the other. However, when a broken power law is adopted they clearly indicate a low-luminosity slope ~= -0.6 +/- 0.2, compatible with the prediction of the internal shock model