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) represents a new spectral component whose temperature is estimated to be 1.8 million K, and luminosity to be 1.7 x 10 to the 42nd erg/s, if it is thermal emission from a hot gas. The observed variable UV and X-ray continua are well correlated down to a time scale of days, and the standard model of a power law with a uniform cold absorber gives a bad fit at low energies in the 1.2-25 keV range. The spectral index of the power law is found to correlate closely with the flux in the 2-10 keV range, with a shallower slope for lower intensity, and the iron fluorescence line at 6.4 keV is seen to respond very slowly to changes in the continuum.
Perola, G.c., Piro, L., Altamore, A., Fiore, F., Boksenberg, A., Penston, M.v., et al. (1986). NEW RESULTS ON THE X-RAY-EMISSION AND ITS CORRELATION WITH THE ULTRAVIOLET IN NGC-4151. THE ASTROPHYSICAL JOURNAL, 306(2), 508-521 [10.1086/164360].
NEW RESULTS ON THE X-RAY-EMISSION AND ITS CORRELATION WITH THE ULTRAVIOLET IN NGC-4151
ALTAMORE, Aldo;
1986-01-01
Abstract
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) represents a new spectral component whose temperature is estimated to be 1.8 million K, and luminosity to be 1.7 x 10 to the 42nd erg/s, if it is thermal emission from a hot gas. The observed variable UV and X-ray continua are well correlated down to a time scale of days, and the standard model of a power law with a uniform cold absorber gives a bad fit at low energies in the 1.2-25 keV range. The spectral index of the power law is found to correlate closely with the flux in the 2-10 keV range, with a shallower slope for lower intensity, and the iron fluorescence line at 6.4 keV is seen to respond very slowly to changes in the continuum.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
