We present results from photometric observations of the dwarf nova system HT Cas during the eruption of 1995 November. The data include the first two‐colour observations of an eclipse on the rise to outburst. They show that during the rise to outburst the disc deviates significantly from steady‐state models, but the inclusion of an inner‐disc truncation radius of about 4Rwd and a ‘flared’ disc of semi‐opening angle of 10° produces acceptable fits. The disc is found to have expanded at the start of the outburst to about 0.41RL1, as compared with quiescent measurements. The accretion disc then gradually decreases in radius reaching < 0.32RL1 during the last stages of the eruption. Quiescent eclipses were also observed prior to and after the eruption and a revised ephemeris is calculated.
We measured the I-band orbital light curve of the soft X-ray transient GS 2000+25 in 1992 August, and the Rand I-band light curves between 1998 September and 2000 August. The light curves are dominated by the ellipsoidal variations of the secondary star in the system. The light curves also showed transient distortions that persisted through individual observing runs, but were diluted and nearly absent in the mean light curve. A small, residual distortion in the mean light curve is consistent with extra flux from a bright spot where the stream of material from the secondary star interacts with the accretion disk around the compact star. The light curve does not show eclipses. The best fits to the mean light curve were achieved with a model that included ellipsoidal variations of the secondary star plus a bright spot on the edge of the accretion disk. The flux from the accretion disk is not well constrained but must be less than 32% of the total R-band flux. Combining our data with previously published spectroscopy of GS 2000+25, we find that the mass of the compact star lies in the range 5:5 P M 1 =M P 8:8, and therefore it is a black hole. The derived mass of the secondary star depends sensitively on the mass ratio, which is measured from the rotational broadening of the absorption lines in the secondary's spectrum. We find 0:16 P M 2 =M P 0:47, but we deem this result less secure than the mass for M 1 . The radius and spectral type (K5) of the secondary are not consistent with those of main-sequence stars with masses in this range but are consistent with an evolved star that has been stripped of mass.
Abstract. We present HST UV observations of the high-inclination low mass X-ray binary AC211 (X2127+119), which is located in the globular cluster M 15 (NGC 7078). We have discovered a C P Cygni profile in this system, which confirms the existence of an outflow from AC211. The outflow velocity as measured from the P Cygni profile is 1500 km s −1 . We calculate that the mass lost through this wind is too small to support a large period derivative as favoured by Homer & Charles (1998). Using new X-ray observations we have revised the ephemeris for AC211 and we find no evidence in support of a period derivative. The UV spectrum exhibits several absorption features due to O, Si and C. The very strong He line at 1640 Å is not seen to modulate strongly with orbital phase, suggesting its origin lies in the outer parts of the system. In contrast, the eclipse of the UV continuum is short compared with the X-ray and optical eclipses.
Context. It has been claimed that the nova-like cataclysmic variable AE Aquarii (AE Aqr) is a very-high-energy (VHE, E > 100 GeV) source both on observational and theoretical grounds. Aims. We search for VHE γ-ray emission from AE Aqr during different states of the source at several wavelengths to confirm or rule out previous claims of detection of γ-ray emission from this object. Methods. We report on observations of AE Aqr performed by MAGIC. The source was observed during 12 h as part of a multiwavelength campaign carried out between May and June 2012 covering the optical, X-ray, and γ-ray ranges. Besides MAGIC, the other facilities involved were the KVA, Skinakas, and Vidojevica telescopes in the optical and Swift in X-rays. We calculated integral upper limits coincident with different states of the source in the optical. We computed upper limits to the pulsed emission limiting the signal region to 30% of the phaseogram and we also searched for pulsed emission at different frequencies applying the Rayleigh test. Results. AE Aqr was not detected at VHEs during the multiwavelength campaign. We establish integral upper limits at the 95% confidence level for the steady emission assuming the differential flux proportional to a power-law function dφ/dE ∝ E −Γ , with a Crab-like photon spectral index of Γ = 2.6. The upper limit above 200 GeV is 6.4 × 10 −12 cm −2 s −1 and above 1 TeV is 7.4 × 10 −13 cm −2 s −1 . We obtained an upper limit for the pulsed emission of 2.6 × 10 −12 cm −2 s −1 for energies above 200 GeV. Applying the Rayleigh test for pulsed emission at different frequencies we did not find any significant signal. Conclusions. Our results indicate that AE Aqr is not a VHE γ-ray emitter at the level of emission previously claimed. We have established the most constraining upper limits for the VHE γ-ray emission of AE Aqr.
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