Extended soft X-ray emission from NGC 4151

Abstract

Extended X-ray emission associated with radio and optical jets has been reported in different types of active galaxies (see the review articles by E. Feigelson and by P. Biermann, both in this volume). The extended radio and optical features in the Seyfert galaxy NGC4151 are much weaker than in other active galaxies, and only careful optical (Ulrich, 1973; Fricke and Reinhardt, 1974) and radio (Wilson, 1981) measurements have revealed weak resolved emission, associated with the active nucleus. A program of long (∿ 104 sec) EINSTEIN- High Resolution Imager (Giacconi et al. 1979, Henry et al. 1977) observations of nearby Seyferts with resolved optical or radio features has been undertaken. NGC4151 seemed the best candidate for extended X-ray emission for the following reasons: Holt et al. (1980) reported that NGC4151 shows an excess of soft (< 1 keV) X-rays over that expected from an extrapolation from higher energies. This excess matches the peak response of the HRI which is around 0.7 keV. Besides that, the large and variable (NH ∿ 10 23 atoms cm-2, Barr et al. 1977) low energy cut-off in the nucleus eases the dynamic range problem of searching for weak features near a strong source.