Search Publications
The X-ray spectrum and variability of Markarian 421.
McHardy, I.; Warwick, R. S.; George, I. M. +1 more
The X-ray bright BL Lac object Markarian 421 (Mrk 421) was observed by Exosat four times over a period of 6 days in February 1984. The source exhibited a very soft power-law X-ray spectrum (photon spectral index is about 2.8) with an extremely low intrinsic column density (less than or equal to 10 to the 20th/sq cm). Significant X-ray variability …
Simultaneous X-ray and optical monitoring of the flare star YZ CMi.
Doyle, J. G.; Rodono, M.; Butler, C. J. +1 more
Broad-band photometric observations of YZ CMi show a 1.2 mag U-band flare, however, simultaneous X-ray observations from EXOSAT show no detectable increase. It is suggested that the event could have occurred low down in a part of the chromosphere, which may not have been coupled to the transition region and corona via magnetic fields. However, a m…
X-ray and optical observations of a dMe flare star in the T Tauri field.
Charles, P. A.; Jordan, C.; Walter, F. +3 more
The authors present observations of a newly discovered dMe flare star within 20 pc of the Sun. An EXOSAT observation of this source shows an almost complete X-ray flare light curve with rise time ≡600 s, decay time ≡1500 s, and peak luminosity Lx = 6.1×1029erg s-1, a 40-fold increase in brightness over the quiescen…
IUE observations of the highly luminous Seyfert galaxy ESO 113-IG45 (Fairall 9).
Penston, M. V.; Moles, M.; Masegosa, J.
Ultraviolet variations of the continuum in ESO 113-IG45 with a doubling time of 50 days indicate a maximum size of 1×1017cm to the emitting region. Power law and blackbody fits to the continuum are both possible. The power-law fit is preferred because of the observed correlation between flux and spectral index which is similar to that f…
EXOSAT observations of a strong soft X-ray excess in MKN 841.
Culhane, J. L.; Fabian, A. C.; Branduardi-Raymont, G. +6 more
EXOSAT observations of the spectrum of the Seyfert 1 galaxy MKN 841 show that it is well-fitted by a power law of photon index 1.6, similar to that of other Seyferts, and a large additional soft component. The X-ray luminosity over the observed band exceeds 4×1044erg s-1. A single-temperature blackbody fit to the soft X-rays …
The old nova GK Per : discovery of the X-ray pulse period.
King, A. R.; Watson, M. G.; Osborne, J.
EXOSAT observations of GK Per during an optical outburst are reported. The hard X-ray emission (greater than 2 keV) shows a strong coherent modulation at a period of 351 s, identifying GK Per as the latest member of the 'intermediate polar' subclass of magnetic cataclysmic variables. The X-ray pulse profile has a quasi-sinusoidal shape with mean a…
Ultraviolet spectral evolution and heavy element abundances in nova Coronae Austrinae 1981.
Williams, R. E.; Truran, J. W.; Wyckoff, S. +3 more
Nova CrA 1981, a moderately fast galactic nova, was systematically observed over a period of seven months with the IUE satellite. The initial evolution of the UV spectrum was similar to that of previously observed novae; however, several months after maximum, weak emission due to very high ionizating forbidden lines of Na, Mg, Al, and Si appeared,…
Continuous rapid X-ray variability and spectral changes in NGC 4051.
Elvis, M.; Watson, M. G.; Lawrence, A. +1 more
The observation of rapid X-ray variability in active galaxies is of great potential interest. In Seyfert galaxies, variability on a time-scale of days seems common, but fast (minutes-hours) variability is apparently very rare. In a variability survey with the HEAO-1 A2 experiment, Tennant and Mushotzky (1983) found only one object to vary on short…
Detailed observations of NGC 4151 with the IUE - IV. Absorption line spectrum and variability.
Tanzi, E. G.; Perola, G. C.; Boksenberg, A. +7 more
A detailed analysis is presented of the ultraviolet (λλ1150 - 3200 Å) absorption spectrum of the NGC 4151 Seyfert nucleus. The IUE data base consisted of high-dispersion (Δλ ≡ 0.2 Å) spectra at 5 epochs, and 137 low-dispersion (Δλ ≡ 4 - 8 Å) spectra at 31 epochs from 1978 February to 1980 May, together with further low-dispersion data in 1980 - 81…
The discovery of low-level iron K line emission from CYG X-1.
White, N. E.; Barr, P.; Page, C. G.
The results of seven observations of the X-ray spectrum of Cyg X-1, made using the gas scintillation proportional counter on board the Exosat Observatory are presented. The discovery of a broad emission feature at 6.2 keV is reported with an equivalent width of typically 120 eV. The line is resolved to have an FWHM of about 1.2 keV. There is no ev…