Far-ultraviolet observations of NGC 4151 during the ORFEUS-SPAS II mission

摘要

We observed the Seyfert 1 galaxy NGC 4151 on 11 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 AA resolution with a total exposure of 15,658 s. The mean flux at 1000 A was 4.7 X 10~-13 ergs cm~-2 s~-1 A~-1. We identify the neutral hydrogen absorption with a number of components that correspond to the velocity Distribution of H I seen in our own Galaxy as well as features identified in the C IV λ1549 absorption profile By Weymann et al. The main component of neutral hydrogen in NGC 4151 has a total column density of log N_H _I = 18.7±1.5 cm~-2 for a Doppler parameter b = 250±50 km s~-1, and it covers 84/100±6/100 of the source.