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Correlated hard X-ray and ultraviolet variability in NGC 5548Contemporaneous 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.
Document ID
19920061186
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Clavel, J.
(ISO Observatory Noordwijk, Netherlands)
Nandra, K.
(Leicester, University United Kingdom)
Makino, F.
(Institute of Space and Astronautical Science Sagamihara, Japan)
Pounds, K. A.
(Leicester, University United Kingdom)
Reichert, G. A.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Urry, C. M.
(Space Telescope Science Institute Baltimore, MD, United States)
Wamsteker, W.
(IUE Observatory Madrid, Spain)
Peracaula-Bosch, M.
(NASA Goddard Space Flight Center Greenbelt, MD, United States)
Stewart, G. C.
(Leicester, University United Kingdom)
Otani, C.
(Institute of Space and Astronautical Science Sagamihara, Japan)
Date Acquired
August 15, 2013
Publication Date
July 1, 1992
Publication Information
Publication: Astrophysical Journal, Part 1
Volume: 393
Issue: 1, Ju
ISSN: 0004-637X
Subject Category
Astrophysics
Accession Number
92A43810
Distribution Limits
Public
Copyright
Other

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