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ngc3516 contains the strongest uv absorption system known in a seyfert 1 galaxy .
this system contains at least two distinct components : a broad ( fwhm@xmath02000 km / s ) variable component and a narrow ( @xmath0500 km / s ) non - variable component .
both the broad and the narrow systems contain high as well as low ionization absorption lines .
recent observations have shown that the broad high ionization absorption lines have * _ disappeared _ * since @xmath01992 ( koratkar et al .
1996 and references therein , kriss et al .
1996 )    we analyze a high signal - to - noise ( s / n ) rosat pspc archival spectrum of ngc3516 obtained in 1992 .
the high s / n allows the strong detection of both ovii and oviii edges independently , in spite of the limited spectral resolution of the pspc .
a warm absorber fit to the data shows that the absorber is highly ionized ( u@xmath1 ) , and has a large column density n@xmath2 @xmath3 .
in several agn , the x - ray and the uv absorbers were found to be one and the same ( the ` xuv ' absorbers , mathur et al . 1994 , 1995 ) .
is it also true for ngc3516 ?
the absorption systems in ngc3516 are clearly complex with multiple components ( kriss et al .
it is the _ high ionization , broad _ absorption system that is most likely to be associated with the x - ray warm absorber .
investigation of this question is tricky , however , because the broad absorption lines have disappeared .
here we argue that the xuv absorption picture is _ consistent _ with the presence of a highly ionized x - ray absorber and the current non - detection of civ and nv broad absorption lines ( see fig .
1 ) . the x - ray absorber _ must _ have a uv signature showing ovi absorption lines ( fig .
1 ) . since there were no simultaneous rosat & far - uv observations in 1992 , this can not be directly determined .
however , we note that in the 1995 hut observations , ovi doublets are unresolved , but consistent with being broad ( fwhm=1076@xmath4146 km / s , kriss et al .
1996 ) .
we argue that the xuv absorber in ngc3516 has evolved with time ( fig .
* pre-1992 : * it showed broad , high ionization civ and nv absorption lines and an x - ray ionized absorber ( u 7 ) .
as it evolves , outflowing and expanding , the density falls and the ionization parameter increases .
* 1992 : * civ and nv absorption lines disappeared ; x - ray absorber is still present with ovi lines in the uv ( u@xmath010 ) ( no uv data available to verify ) .
* 1995 : * civ and nv absorption line remain absent ; x - ray absorber is present .
ovi lines are present , and detected with hut ( u@xmath013.5 ) .
* post-1996 : * we predict that the ovi absorption lines will disappear as the ionization parameter increases further ( u20 )
. the oviii edge will continue to strengthen relative to the ovii edge .
eventually , even the x - ray absorber will also disappear .
ferland ,  g.  f. 1991 `` hazy '' , osu astronomy department internal report kriss , g. et al .
1996 , apjl , in press koratkar , a. et al .
1996 , apj , in press mathur ,  s. , wilkes ,  b. , elvis ,  m. & fiore , f. 1994 , apj , 434 , 493 mathur ,  s. , elvis ,  m. & wilkes ,  b. 1995 , apj , 452 , 230
for ngc3516 we find that the x - ray warm absorption and the broad uv associated absorption features can be produced by the same absorbing material . 
 we argue that the evolution of the xuv absorber from pre-1992 to 1995 is consistent with expectation for an expanding , outflowing material .