Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-ray vs. Optical Variations in the Seyfert 1 Nucleus NGC 3516: A
  Puzzling Disconnectedness   We present optical broadband (B and R) observations of the Seyfert 1 nucleus
NGC 3516, obtained at Wise Observatory from March 1997 to March 2002,
contemporaneously with X-ray 2-10 keV measurements with RXTE. With these data
we increase the temporal baseline of this dataset to 5 years, more than triple
to the coverage we have previously presented for this object. Analysis of the
new data does not confirm the 100-day lag of X-ray behind optical variations,
tentatively reported in our previous work. Indeed, excluding the first year's
data, which drive the previous result, there is no significant correlation at
any lag between the X-ray and optical bands. We also find no correlation at any
lag between optical flux and various X-ray hardness ratios. We conclude that
the close relation observed between the bands during the first year of our
program was either a fluke, or perhaps the result of the exceptionally bright
state of NGC 3516 in 1997, to which it has yet to return. Reviewing the results
of published joint X-ray and UV/optical Seyfert monitoring programs, we
speculate that there are at least two components or mechanisms contributing to
the X-ray continuum emission up to 10 keV: a soft component that is correlated
with UV/optical variations on timescales >1 day, and whose presence can be
detected when the source is observed at low enough energies (about 1 keV), is
unabsorbed, or is in a sufficiently bright phase; and a hard component whose
variations are uncorrelated with the UV/optical.

37
The categories of this paper are: supr-con
27
The categories of this paper are: comp-gas
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph
36
The categories of this paper are: cmp-lg
32
The categories of this paper are: atom-ph
18
The categories of this paper are: econ
12
The categories of this paper are: nucl-th
16
The categories of this paper are: stat
28
The categories of this paper are: alg-geom
21
The categories of this paper are: adap-org
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
25
The categories of this paper are: patt-sol
31
The categories of this paper are: ao-sci