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The Discovery of 3.8 Hour Periodic Intensity Dips and Eclipses from the Transient Low-Mass X-Ray Binary EXO 0748-676
Parmar, A. N.; White, N. E.; Giommi, P. +1 more
Using the EXOSAT Observatory the authors have discovered a new transient X-ray burst source EXO 0748-676 that shows 8.3 minute duration X-ray eclipses that recur with a period of 3.82 hr. If the companion star is on the main sequence, the eclipse duration gives a companion mass of 0.45 M_sun; and a system inclination of 75°. Irregular intensity di…
X-Ray and Optical Observations of the Ultrashort Period Dwarf Nova SW Ursae Majoris: A Likely New DQ Herculis Star
Szkody, P.; Shafter, A. W.; Thorstensen, J. R.
Optical photometric and spectroscopic and X-ray observations of the dwarf nova SW UMa are presented. Moderate resolution spectroscopic data have established an orbital period of 81.8 min and have revealed that the Balmer emission lines have a multiple structure. A narrow component, similar to the s-wave component which is sometimes seen in catacly…
New Results on the X-Ray Emission and Its Correlation with the Ultraviolet in NGC 4151
Piro, L.; Perola, G. C.; Altamore, A. +8 more
Results from observations of the Seyfert galaxy NGC 4151 obtained with Exosat (0.1-25 keV) and IUE (1200-3000 A) during November 1983, and between December 1984 and January 1985, are presented. The stability of the flux during large-scale variations in the UV and X-ray regions suggests that the soft X-ray excess noted by Holt et al. (1980) represe…
EXOSAT Observations of the 35 Day Cycle of Hercules X-1: Evidence for Neutron Star Precession
Pietsch, W.; Kahabka, P.; Truemper, J. +2 more
Her X-1 was observed with Exosat throughout a 35 day cycle at about 4 day sampling intervals. These measurements include, for the first time, an accurate determination of the 1.24 s pulse profiles during the short-on state at the middle of the 35 day cycle. The data show a large change in the pulse profiles between the main and short-on states, su…
Bimodal Quasi-oscillatory and Spectral Behavior in Scorpius X-1
Stella, L.; Priedhorsky, W.; Lewin, W. H. G. +4 more
Exosat observations of Sco X-1 obtained using the Xe and/or Ar detectors for a total of about 80,000 s during four runs on August 24-27, 1985 are reported and analyzed. Two modes of quasi-periodic oscillations (QPOs) corresponding to the quiescent and active states of Sco X-1 and to two modes of spectral behavior are identified and characterized, …
An EXOSAT Observation of Quiescent and Flare Coronal X-Ray Emission from Algol
Parmar, A. N.; White, N. E.; Culhane, J. L. +4 more
X-ray emission from the Algol system is believed to originate in a corona associated with the K star. The authors have used the EXOSAT Observatory to make a 35 hr continuous observation centered on the occultation of the K star by the B star primary. The spectrum of the quiescent emission in the 1 - 10 keV band gives a temperature of 2.5×107<…
The Bursting Behavior of the Transient X-Ray Burst Source EXO 0748-676: A Dependence between the X-Ray Burst Properties and the Strength of the Persistent Emission
Haberl, F.; Parmar, A. N.; White, N. E. +1 more
Between 1985 February 15 and July 19 EXOSAT made eight observations of the transient X-ray source EXO 0748-676. Within this time interval the persistent flux varied by a factor of 5 from a high to a low state and back to a high state. We observed 26 type I bursts, of which 22 were analyzed in detail. As the persistent flux decreased, the burst fre…
Discovery of Rapid Quasi-periodic Oscillations in Scorpius X-1
Priedhorsky, W. C.; Middleditch, J.
The X-ray flux from Sco X-1 can vary quasi-periodically. Fourier analysis of 5-20 keV X-ray data taken while the source was quiescent shows a power density peak at 6 Hz, with a 2 Hz FWHM, and which corresponds to 5 percent of the flux (rms amplitude). No 6 Hz peak was observed when the source was more active, but rather a broad distribution of exc…
EXOSAT Observations of V471 Tauri: A 9.25 Minute White Dwarf Pulsation and Orbital Phase Dependent X-Ray Dips
Sion, E. M.; Guinan, E. F.; Swank, J. H. +3 more
New results obtained from a 28 hr continuous observation of V471 Tauri with the EXOSAT satellite are reported. The detection of soft X-ray fluxes from both the white dwarf and the K dwarf, the discovery of a 9.25 minute pulsation from the white dwarf, and the discovery of orbital phase-related soft X-ray dips are discussed. The dips may be correla…
The Discovery of 3.9 Hour Periodic Dips in the X-Ray Intensity of XB 1254-690
Parmar, A. N.; Pakull, M.; Courvoisier, T. J. -L. +1 more
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-r…