[en] Having discussed the neutrino production rate in electron-positron pair annihilation reactions in supernovae explosions, a simple model of the core collapse is described and parameters relevant to the neutrino production given explicitly. The neutrino density is described as a function of time and a range estimate given of the time during which the electron-positron pair annihilation may be of some importance to the physics of supernovae. (U.K.)

[en] The discovery of periodic optical variations from the counterpart of the low-mass X-ray binary XB 1254-690 is reported. The period is 0.163890 + or - 0.000009 days, identical to the recurrence period of X-ray dips. The full amplitude of the light curve is 0.4 mag and the mean V-magnitude is 19.1. From spectrophotometric observations the authors derive a B-V color index of 0.31 + or - 0.05 and an interstellar reddening of E(B-V) = 0.4 + or - 0.1. The optical minimum occurs 0.15 in phase after X-ray dips. Most of the optical light curve is probably due to varying aspect of the X-ray-heated secondary atmosphere. The contribution of the X-ray-heated bulge does not dominate the optical variability. The X-ray-heated secondary explanation supports the interpretation that the X-ray dips are due to eclipses by a bulge located on the edge of the accretion disk and indicates that at least in the case of XB 1254-690 the accretion disk does not shadow completely the companion star. 37 references

[en] The low-mass X-ray binary XB 1254 - 690 has been discovered to show irregular dips in X-ray intensity that recur with a period of 3.9 hr consistent with the optical period derived independently. The spectral changes observed during dipping are complex and can be successfully described using a two-component model. One of these components may be X-rays scattered into the line of sight by an accretion disk corona. In contrast to other X-ray dipping sources for which the metallicity has been measured, the abundance of the material responsible for the dips is close to that of cosmic material. 29 references

[en] Context. In its first 4 years of observing the sky above 20 keV, INTEGRAL-ISGRI has detected 500 sources, around half of which are new or unknown at these energies. Follow-up observations at other wavelengths revealed that some of these sources feature unusually large column densities, long pulsations, and other interesting characteristics. Aims. We investigate where new and previously-known sources detected by ISGRI fit in the parameter space of high-energy objects, and we use the parameters to test correlations expected from theoretical predictions. For example, the influence of the local absorbing matter on periodic modulations is studied for Galactic High-Mass X-ray Binaries (HMXBs) with OB supergiant and Be companions. We examine the spatial distribution of different types of sources in the Milky Way using various projections of the Galactic plane, in order to highlight signatures of stellar evolution and to speculate on the origin of the group of sources whose classifications are still uncertain. Methods. Parameters that are available in the literature, such as positions, photoelectric absorption (N_H), spin and orbital periods, and distances or redshifts, were collected for all sources detected by ISGRI. These values and their references are provided online. Results. ISGRI has detected similar numbers of X-ray Binaries and Active Galactic Nuclei (AGN). The former group contains new members of the class of HMXBs with supergiant stellar companions. Usually, this type of object presents strong intrinsic absorption which leads to a peak emission in an energy range that ISGRI is ideally suited to detect. Thanks to these additional systems, we are able to show that HMXBs are generally segregated in plots of intrinsic (N_H) versus the orbital period of the system and versus the spin period of the pulsar, based on whether the companion is a Be or an OB supergiant star. We also find a tentative but expected anticorrelation between (N_H) and the orbital period, and a possible and unexpected correlation between the (N_H) and the spin period. While only a handful of new Low-Mass X-ray Binaries (LMXBs) have been discovered, there are many sources that remain unclassified and they appear to follow a spatial distribution typical of Galactic sources (especially LMXBs) rather than extragalactic sources. (authors)