The flux variability of the Seyfert galaxy NGC6814 as observed with exosat

Abstract

We present five EXOSAT observations of the Seyfert galaxy NGC6814. The source is found to be variable at both soft (LE) and medium (ME) X-ray energies. The most remarkable characteristics of this variability are the regular recurrence of flares at 12000s intervals during a 1-day long ME observation, a dip in the ME flux by a factor of 2 in ~ 300 s, and variable low-energy absorption in the X-ray spectrum on a timescale of months. The EXOSAT observations support the conclusion reached by Tennant et al. (1981) /1/ on the basis of HEAO-A2 observations that the X-ray behaviour of NGC6814 is unsual among AGN. We consider possible scenarios in which such behaviour may originate, and briefly discuss the issue of a `characteristics' timescale of the variability of AGN.