A search for rapid variability in the broad Hα profiles of seyfert and radio galaxies

We present the results of a search for rapid variability (on time scales of hours to days) in the Hα profiles of eight nearby Seyfert galaxies and broad-line radio galaxies. The purpose of the search was to look for specific evidence of reverberation from an accretion disk in response to flaring of the source of ionizing radiation. Line-profile variations of the kind predicted by Stella are expected to occur on time scales shorter than the light-crossing time of the disk, which can be as short as a day. We pay particular attention to broad-line radio galaxies with double-peaked line profiles which are very likely to originate in an accretion disk (such as Arp 102B and 3C 390.3). Our results are largely negative in that they reveal no profile variability in the Hα profiles of any of the target objects at the 1% level on time scales of a few days or less. We do, however, find variability in some objects on time scales of 10 days or more. NGC 5548 exhibits profile variations over intervals of 12 days to a year, and NGC 4151 and Mrk 6 exhibit profile variations over intervals of 6 months to a year, which suggest that the broad Hα lines may consist of several components that do not vary in concert.