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The X-ray emission of 3C 273.
Koyama, K.; Nandra, K.; Tanaka, Y. +12 more
The X-ray emission of 3C273 in the 0.2-35 keV band has been studied, with EXOSAT and Ginga, over the period 1983 December to 1985 December. The overall flux is variable on a time-scale of weeks by a factor of 2. The spectral index in the 2-10 keV band (α ~0.5) is significantly different from the 'canonical' AGN index of α = 0.7. There are small bu…
The variable X-ray absorption and soft X-ray excess of the QSO MR 2251-178.
Pounds, K. A.; Stewart, G. C.; Pan, H. C.
We present the results from a programme of 15 EXOSAT observations in which we monitored the QSO MR2251 - 178. Over the period 1983 October-1984 December the hard X-ray flux varied by a factor of 2. While there is an overall correlation between the ME(2-10 keV) and LE(0.1-2 keV) fluxes the pattern of variability is such that it cannot be described …
The ephemeris of X 1822-371.
Hellier, Coel; Mason, Keith O.; Smale, Alan P. +1 more
From the analysis of eclipses observed with the HEAO-1, Einstein, Exosat and Ginga satellites, it is shown that the orbital period of X1822 - 371 is increasing on a time-scale of 2.9 million yr. The period change, one of only three determined amongst the LMXBs, is in the opposite sense to the expected evolutionary trend, but in the same sense as t…
Localization of one of the galactic centre X-ray burst sources.
Skinner, G. K.; Eyles, C. J.; Foster, A. J. +1 more
Observations of an X-ray burst which occurred during the Spacelab-2 observations of the Galactic Center region are reported, and it is shown that it originated in the more southerly component of a previously reported persistent X-ray object, now resolved into two sources separated by 3 arcmin. Present knowledge of the number and location of the Ga…
The X-ray orbital lightcurve of TY Pyx : a 3.2-day eclipsing RS CVn system.
Parmar, A. N.; White, N. E.; Culhane, J. L. +1 more
An Exosat observation of one orbital cycle of the eclipsing 3.2-d RS CVn system TY Pyx is reported. This system contains two almost identical GV stars, which is unusual because most RS CVns contain F or G main-sequence star and a K subgiant. The X-ray light curves of the primary and secondary eclipses are different above and below 1 keV. At lower …
X-ray spectral variations in NGC 4151.
Perola, G. C.; Fiore, F.; Romano, M.
In their analysis of the EXOSAT ME data on the Seyfert NGC 4151, Yaqoob, Warwick & Pounds found that the observed tendency of the spectrum to soften as the X-ray flux increases is due to variations in the absorbing column, which are anti-correlated with the source intensity, thus favouring a 'warm absorber' model. In this paper a re-analysis o…
Coronal X-ray emission from the short-period eclipsing binary XY UMa.
Jeffries, R. D.; Bedford, D. K.; Vilhu, O. +1 more
XY UMa, a close binary showing photospheric and chromospheric activity, has been observed with Exosat through 1.26 orbital cycles, with supporting optical photometry. The G2-5 V primary star is found to be responsible for the observed soft X-ray flux, which shows a clear primary eclipse. The X-ray-emitting coronal plasma is modeled to have two com…
Is V426 Ophiuchi really an intermediate polar ?
Hellier, Coel; O'Donoghue, Darragh; Buckley, David +1 more
The dwarf nova V426 Oph has been proposed as an intermediate polar with a report of a 60-min period in the X-ray band. Optical photometry and spectroscopy show no evidence for such a period. Additionally, reanalysis of the X-ray data shows that the 60-min period is not significant and that the variability is consistent with flickering. Overall, no…
Self-consistent comptonized models for the spectra of low-mass X-ray binaries.
Ross, R. R.; Ponman, T. J.; Foster, A. J.
We have constructed Comptonized spectral models and fitted them to EXOSAT spectra of eleven bright low-mass X-ray binaries. The models are based on the premise that these systems contain circumstellar material which modifies the X-ray spectrum passing through it. We idealize this situation as a point source of X-rays, the neutron star, embedded in…
X-ray observations of the radio galaxy Pictor A.
Singh, K. P.; Rao, A. R.; Vahia, M. N.
strong X-ray emission is detected from the active nucleus of an emission- line radio galaxy Pictor A, during observations with the EXOSAT observatory. The nuclear X-ray emission is observed to be steady on time- scales of a few minutes to a few hours. The X-ray spectrum is adequately explained by a simple power law with the photon index {GAMMA} = …