Search Publications
GK Per : X-ray observations in quiescence.
King, A. R.; Watson, M. G.; Norton, A. J.
Two X-ray observations of GK Per in quiescence made with Exosat are presented. The X-ray light curve obtained on both occasions shows clear evidence for the 351-s pulse period first discovered during an earlier outburst. The pulse profile in the first of the two quiescent observations is similar to that observed during outburst, albeit with lower …
Quasi-periodic Oscillations in the X-Ray Flux of the Rapid Burster (MXB 1730-335)
Haberl, F.; Stella, L.; Parmar, A. N. +3 more
The authors report on the results of an EXOSAT observation of the "Rapid Burster" in 1985 August during an active state. Forty 1 - 10 minute long type 2 bursts were detected together with persistent emission. Quasi-periodic oscillations (QPO) were observed in 23 bursts with frequencies between 2 and 5 Hz. The average frequency of the QPO during th…
A correlation between Balmer and soft X-ray emission from stellar andsolar flares.
Foing, B. H.; Rodono, M.; Butler, C. J.
Simultaneous optical spectroscopy and X-ray monitoring of stellar and solar flares shows that a well-defined linear correlation exists between the integrated Hγ and soft X-ray flux that extends over four orders of magnitude. The existence of this relationship implies a direct proportionality between the emission from the cooler and denser regions …
Spectroscopy of the M 15 X-ray source : discovery of binary motion and an unusual systemic velocity.
Charles, P. A.; Hassall, B. J. M.; Naylor, T. +1 more
The authors present the first phase-resolved optical spectroscopy of AC 211, the optical counterpart of the X-ray source in the core of M15. The spectrum is dominated by the variable and complex He II λ4686 emission, but the authors have also found He I in absorption. By following the motion of He I λ4471 they have discovered the binary period to …
The Discovery of the 2 Hour Modulated X-Ray Source EXO 033319-2554.2, an AM Herculis System
Tagliaferri, G.; Stella, L.; Giommi, P. +2 more
The authors report the discovery of EXO 033319-2554.2, a soft X-ray source with 100% modulation of its soft X-ray flux, found during a systematic analysis of all of the EXOSAT soft X-ray data. The soft X-ray light curve, which has an on-off behavior, shows a period of 127.7±3.0 minutes. The bright part of the cycle lasts 0.55 in phase and is cut b…
The optical and UV spectrum of the Seyfert type 2 galaxy NGC 3393.
Prieto, M. A.; Wamsteker, W.; Diaz, A. I.
The combined UV and optical spectrum of the Seyfert type 2 galaxy NGC 3393 is presented and analyzed together with published IR and IRAS data. The conditions in the narrow line gas strongly suggest that the high ionization material is in a zone of higher density (N_e_=10^5^ cm^-3^) while the low ionization material is at N_e_=10^3^ cm^-3^. No evid…
Spectroscopy of the present extraordinary bright outburst phase of the LMC S DOR variable R 127.
Stahl, O.; Wolf, B.; Smolinski, J. +1 more
We observed the S Dor variable R 127 in 1986, August 22, when it was the visually brightest star of the LMC at high dispersion in the optical range with CASPEC. We discuss this echelle spectrogram together with spectra taken at earlier epochs with the same instrument to study the spectral evolution of R 127 during outburst. In addition a high disp…
New constraints on neutron star models of gamma-ray bursts. I. EXOSATobservations of two gamma-ray burst error boxes.
Hurley, K.; Boer, M.; Niel, M. +13 more
Two EXOSAT observations of gamma-ray burst error boxes and their possibly associated optical transients are discussed. No point source was detected in either box. A comparison with Einstein data (Pizzichini et al., 1986) is made for one of them (November 19, 1978). The data are interpreted in the framework of neutron star models for gamma-ray burs…
Rotational modulation and flares on RS CVn and BY DRA systems. VIII. Simultaneous EXOSAT and H alpha observations of a flare on the dMe star GL 644 AB (Wolf 630) on 24/25 August 1985.
Tagliaferri, G.; de La Reza, R.; White, N. E. +5 more
A large flare was detected simultaneously in X-rays and H-alpha on the visual binary Gl 644 AB at about 00:15 UT on August 25, 1985. The flare was detected with both the low (0.05-2 keV) and medium energy (2-7 keV) experiments onboard Exosat, with the flare rise time being similar in both the low and medium energy ranges, although in the low energ…
Variable low-energy absorption in the X-ray spectrum of ESO 103-G35.
Turner, T. J.; Warwick, R. S.; Pounds, K. A.
EXOSAT observations of the Seyfert 1.9 galaxy, ESO 103-G35, have revealed that this source has a heavily absorbed and variable low-energy X-ray spectrum. Specifically the inferred column density was observed to decrease from ~1.7x10^23^ to ~1.0x10^23^ cm^-2^ over a 90-day period. This variation is interpreted in terms of an X-ray absorbing screen …