Van den Heuvel et al. (1992) argued that the emission from supersoft X-ray sources can be explained by steady nuclear burning of hydrogen accreted onto massive white dwarfs. An argument that has been used against this model is that the bolometric luminosities inferred from blackbody fits are sometimes above the Eddington luminosity of a ∼1 M⊙ star. However, hot white dwarfs don't radiate blackbody spectra (Heise et al. 1994). Therefore, we have calculated model spectra for hot (accreting) white dwarfs, and investigated whether the emission from supersoft X-ray sources is consistent with an origin from white dwarfs. Here we summarize some preliminary results. For a review of supersoft X-ray sources we refer to the contribution of Kahabka & Trümper to these proceedings.

CH Cyg and MWC 560 are very peculiar symbiotic binaries consisting of an M giant and a white-dwarf companion. The systems have many features in common. In particular, both show occasional eruptions with sub-Eddington luminosity accompanied by flickering activity, and appearance of high-velocity jets. We present arguments that objects like CH Cyg and MWC 560 form a new subclass of interacting binaries distinguished by the presence of wind accreting magnetic white dwarfs.

We present here a study of the five reported outbursts of the recurrent nova RS Ophiuchi, together with an analysis of its light variation between outbursts. We find that the shapes and decline rates of the outbursts are strikingly similar to each other. We note the possibility of an additional, unreported outburst in 1945, supported by the similarity of its decline to that of other outbursts. Each interval between outbursts shows periodicity within itself, however, there is no periodicity common to all, and the possible periods range between 892 and 2283 days.

Gamma-ray bursts remain one of the greatest mysteries in astrophysics in spite of new and more detailed observations made with the BATSE experiment on the Compton Observatory. The new observation with the greatest impact has been the observed isotropic distribution of bursts along with a deficiency of the weak bursts which would be expected from a homogeneous burst distribution. This is not compatible with any known Galactic population of objects. Other recent important observations include an enormous variety of burst morphologies and gamma-ray burst photons extending to GeV energies. A time dilation effect has also been reported to be observed in gamma-ray bursts.

After the first 4 years of its operation, the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma Ray Observatory (CGRO), detected recurrent emission from two of the three known Soft Gamma Repeater (SGR) sources, SGR 1900+14 and SGR 1806-20. The reactivation of the latter prompted a quick international campaign resulting in the identification of the X-ray counterpart of the source, which also coincides with a compact radio source. The absence of detection of new sources in the 4 years of BATSE operation and the reactivation of two of the three already known SGRs, indicates that these objects are rare. We give here a short review of the previously detected SGR emissions and present the recent results obtained with BATSE.

Neutron star binaries, such as the one observed in the famous binary pulsar PSR 1913+16, end their life in a catastrophic merger event (denoted here NS2M). The merger releases ∼5 1053 ergs, mostly as neutrinos and gravitational radiation. A small fraction of this energy suffices to power γ-ray bursts (GRBs) at cosmological distances. Cosmological GRBs must pass, however, an optically thick fireball phase and the observed γ rays emerge only at the end of this phase. Hence, it is difficult to determine the nature of the source from present observations (the agreement between the rates of GRBs and NS2Ms providing only indirect evidence for this model). In the future a coinciding detection of a GRB and a gravitational-radiation signal could confirm this model.