EXOSAT observations of a 2,000-s intensity dip in Seyfert galaxy NGC 4151

Details EXOSAT observations of a 2,000-s intensity dip in Seyfert galaxy NGC 4151 EXOSAT observations of a 2,000-s intensity dip in Seyfert galaxy NGC 4151

Jun 1985

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1985natur.315..554w&link_type=abstract

Nature (ISSN 0028-0836), vol. 315, June 13, 1985, p. 554, 555.

Astronomy and Astrophysics

Astronomy

9

Exosat Satellite, Galactic Nuclei, Quasars, Seyfert Galaxies, X Ray Sources, Active Galactic Nuclei, Bl Lacertae Objects, Black Holes (Astronomy), Interstellar Matter, Light Curve, Stellar Luminosity

Scientific paper

Variations in the flux from active galactic nuclei (AGN) allow the testing of models of their emission mechanisms. Various suggestions for the energy generation in AGNs require the existence of a compact object, with X-rays generated deep in that object's potential well and, therefore, X-ray luminosity related directly to the object responsible for their enormous luminosities. During a 5-h X-ray observation of NGC 4151, a significant drop in intensity lasting about 2,000 s was observed. The event is similar to a short flux decline previously observed in NGC 6184. Simultaneous intensity monitoring of a quasar with coordinates close to those of NGC 4151 revealed no variability in its flux, allowing instrumental causes of the event to be discounted. The short timescale of the intensity dip imposes limits of 20-300 million solar masses on the mass of the central black hole. It is suggested here that the sudden drop in intensity may have been caused by a change in the ionization state of gas clouds surrounding the black hole or, possibly, by the passage of a star across the line-of-sight in the dense nuclear region of the galaxy.

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