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The Antarctic Muon And Neutrino Detector Array (AMANDA) is a high-energy neutrino telescope operating at the geographic South Pole. It is a lattice of photomultiplier tubes buried deep in the polar ice between 1500 m and 2000 m. The primary goal of this detector is to discover astrophysical sources of high energy neutrinos. A high-energy muon neutrino coming through the earth from the Northern Hemisphere can be identified by the secondary muon moving upward through the detector.The muon tracks are reconstructed with a maximum likelihood method. It models the arrival times and amplitudes of Cherenkov photons registered by the photomultipliers. This paper describes the different methods of reconstruction, which have been successfully implemented within AMANDA. Strategies for optimizing the reconstruction performance and rejecting background are presented. For a typical analysis procedure the direction of tracks are reconstructed with about 2 • accuracy.

Abstract.We have analysed 350 pointed and serendipitous observations of 108 different classical and recurrent novae in outburst and in quiescence, contained in the ROSAT archive. One aim was to search for super-soft X-ray sources and we found only 3 of them among post-novae. Thus, the super-soft X-ray phase of novae is relatively short lived (up to 10 years) and is observed only for up to 20% of novae. Most classical and recurrent novae instead emit hard X-rays (in the ROSAT band) in the first months after the outburst, with peak X-ray luminosity of a few times 10 33 erg s −1 . The emission, which we attribute to shocks in the nova ejecta, lasts at least 2 years and even much longer under special circumstances (like preexisting circumstellar material, or a prolonged wind phase). We also investigated X-ray emission due to the accretion mechanism in quiescent novae. 81 Galactic classical and recurrent novae were observed at quiescence, and only 11 were detected. Some of them are variable in X-rays on time scales of years; the X-ray spectra range from very soft to hard. The average X-ray luminosity is not larger than that of quiescent dwarf novae, even if quiescent novae are at least 10 times more luminous at optical wavelengths. There seems to be a missing boundary layer problem: a possible explanation is that boundary layer radiation in nova systems is emitted almost entirely in the extreme ultraviolet. There is no evidence of a large incidence of magnetic systems, either of enhanced X-ray luminosity in novae observed shortly before or after the outburst.

The telescopes on the Compton Gamma Ray Observatory (CGRO) have observed PSR B1055−52 a number of times between 1991 and 1998. From these data, a more detailed picture of the gamma radiation from this source has been developed, showing several characteristics which distinguish this pulsar: the light curve is complex; there is no detectable unpulsed emission; the energy spectrum is flat, with no evidence of a sharp high-energy cutoff up to >4 GeV. Comparisons of the gamma-ray data with observations at longer wavelengths show that no two of the known gamma-ray pulsars have quite the same characteristics; this diversity makes interpretation in terms of theoretical models difficult.

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