High-rate spectroscopic active galactic nucleus monitoring at the wise observatory. I. Markarian 279

We monitored spectrophotometrically a sample of AGNs, and achieved a temporal sampling rate of once every 3-4 days, over a period of 5-7 months. By observing each object simultaneously with a nearby field star, in a long-slit spectroscopy mode, we obtained accurate flux measurements even during bad weather and full moon. In this paper, the first in a series, we describe our observational technique and reduction procedure in general, and discuss our results for the Seyfert 1 galaxy Mrk 279. This object brightened by 20%-50% in Hα, Hβ, and the optical continuum during the period of observation. The high sampling rate and small error allow the determination, through cross-correlation, of the lag in the emission-line response to the continuum brightening. A lag of 12 days is observed. Using Monte Carlo simulations, we estimate the size of the broadline region (BLR) to be 12 ± 3 light days in this object and find that the results rule out, at the 95% significance level, a BLR of 21 light-days or larger. This result is in conflict with the "standard" photoionization model of AGNs, which predicts a BLR size larger by an order of magnitude.