Gerard A. Kriss, Arthur F. Davidsen, Wei Zheng, Jeffrey W. Kruk and Brian R. Espey
Department of Physics & Astronomy, Johns Hopkins University,
Baltimore, MD 21218
30, and it shows profound differences compared to
that obtained during the flight of Astro-1 in December 1990.
The continuum,
at 1455 Å,
is five times brighter,
the brightest UV flux ever observed for NGC 4151.
All high-ionization absorption lines have strengthened considerably ---
S VI 
,
C III 
,
O VI 
,
N V 
,
Si IV 
, and
C IV 
.
The Lyman series absorption lines have also increased in strength, with
the bulk of the absorption requiring
a neutral hydrogen column density of
covering only 78% of the UV source with
an effective Doppler parameter of 
.
However, up to 
of neutral hydrogen
that fully covers the source could be present in gas with
a thermal Doppler parameter of 
.
Single-zone photoionization models of warm absorbing gas are unable to account
for both the X-ray absorbing material and the UV-absorbing gas, largely because
of the wide range of ionization states present in the UV and the X-ray.
Subject headings: galaxies: active --- galaxies: individual (NGC 4151) --- galaxies: nuclei --- galaxies: Seyfert --- ultraviolet: galaxies