Correlated hard X-ray and ultraviolet variability in NGC 5548

Details Correlated hard X-ray and ultraviolet variability in NGC 5548 Correlated hard X-ray and ultraviolet variability in NGC 5548

Jul 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992apj...393..113c&link_type=abstract

Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 393, no. 1, July 1, 1992, p. 113-125.

Astronomy and Astrophysics

Astrophysics

140

Galactic Clusters, Ginga Satellite, Iue, Seyfert Galaxies, X Ray Sources, Accretion Disks, Astronomical Models, Potassium, Thermal Emission, Ultraviolet Radiation

Scientific paper

Contemporaneous X-ray (from the Ginga satellite) and ultraviolet (IUE) observations of NGC 5548 in 1989-1990 show that the 1350 A and 2-10 keV flux both varied by a factor of 2.6 in a highly correlated fashion. Adding an additional simultaneous IUE-Exosat observation from 1984 significantly weakens the correlation, since the UV flux was 3.5 times larger then than its average 1990 value, while the X-ray flux was only 70 percent higher. In 1990 the UV and X-ray flux variations appear to be simultaneous to within no more than six days. These results, together with the simultaneity of the variations at 5000 and 1350 A, are incompatible with the standard geometrically thin accretion model. They may be explained, however, if part of the UV and optical radiation originates from reprocessing of X-rays emitted above the disk. Thus essentially all the UV flux in 1990 would be due to reprocessing. But the large UV outburst in 1984 probably represents a genuine increase in the disk throughput due to instability in the disk itself. The similar relationship between UV and X-ray emission in NGC 4151 suggests that this scheme may be applicable to Seyfert galaxies as a class.

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