Far-UV Observations of NGC 4151 during the ORFEUS-SPAS II Mission

Abstract

We observed the Seyfert 1 galaxy NGC 4151 on eleven occasions at 1-2 day intervals using the Berkeley spectrometer during the ORFEUS-SPAS II mission in 1996 November. The mean spectrum covers 912-1220 A at ~0.3 A resolution with a total exposure of 15,658 seconds. The mean flux at 1000 A was 4.7e-13 erg/cm^2/s/A. We identify the neutral hydrogen absorption with a number of components that correspond to the velocity distribution of \ion{H}{1} seen in our own Galaxy as well as features identified in the CIV 1549 absorption profile by Weymann et al. The main component of neutral hydrogen in NGC 4151 has a total column density of log N_HI = 18.7 +/- 1.5 cm^{-2} for a Doppler parameter b=250 +/- 50 km/s, and it covers 84 +/- 6% of the source. This is consistent with previous results obtained with the Hopkins Ultraviolet Telescope. Other intrinsic far-UV absorption features are not resolved, but the CIII* 1176 absorption line has a significantly higher blueshift relative to NGC 4151 than the CIII 977 resonance line. This implies that the highest velocity region of the outflowing gas has the highest density. Variations in the equivalent width of the CIII* 1176 absorption line anticorrelate with continuum variations on timescales of days. For an ionization timescale <1 day, we set an upper limit of 25 pc on the distance of the absorbing gas from the central source. The OVI 1034 and HeII 1085 emission lines also vary on timescales of 1-2 days, but their response to the continuum variations is complex. For some continuum variations they show no response, while for others the response is instantaneous to the limit of our sampling interval.

4 pages, 2 PostScript figures, uses emulateapj.sty, apjfonts.sty. To appear in the Astrophysical Journal (Letters) special issue for ORFEUS

References in corpus (2)

• Far-Ultraviolet Performance of the Berkeley Spectrograph During the ORFEUS-SPAS II Mission
• ORFEUS-II Far-Ultraviolet Observations of 3C273: 1. Interstellar and Intergalactic Absorption Lines

Cited by in corpus (15)

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• STIS Longslit Spectroscopy of the Narrow-Line Region of NGC 4151. II. Physical Conditions along Position Angle 221 Degress
• STIS Echelle Observations of the Seyfert Galaxy NGC 4151: Physical Conditions in the Ultraviolet Absorbers
• FUSE Observations of Intrinsic Absorption in the Seyfert 1 Galaxy Mrk 509
• Variable UV Absorption in the Seyfert 1.5 Galaxy NGC 3516: The Case for Associated UV and X-ray Absorption
• Simultaneous Ultraviolet and X-ray Observations of the Seyfert Galaxy NGC 4151. II. Physical Conditions in the UV Absorbers
• The Connection between the Narrow-Line Region and the UV Absorbers in Seyfert Galaxies
• Intrinsic Absorption in the Spectrum of Mrk 279: Simultaneous Chandra, FUSE, and STIS Observations
• HST FOC spectroscopy of the NLR of NGC 4151. I. Gas kinematics
• Multiwavelength studies of the Seyfert 1 galaxy NGC7469. I - Far UV observations with FUSE
• STIS Echelle Observations of NGC 4151: Variable Ionization of the Intrinsic UV Absorbers
• The Effect of Intrinsic UV Absorbers on the Ionizing Continuum and Narrow Emission Line Ratios in Seyfert Galaxies
• Physical Properties of Young Stellar Populations in 24 Starburst Galaxies Observed with FUSE