J. W. Wilson

Multiepoch multiwavelength spectra and models for blazar 3C 279

Of the blazars detected by EGRET in GeV γ-rays, 3C 279 is not only the best observed by EGRET but also one of the best monitored at lower frequencies. We have assembled 11 spectra, from GHz radio through GeV γ-rays, from the time intervals of EGRET observations. Although some of the data have appeared in previous publications, most are new, including data taken during the high states in early 1999 and early 2000. All of the spectra show substantial γ-ray contribution to the total luminosity of the object; in a high state, the γ-ray luminosity dominates over that at all other frequencies by a factor of more than 10. There is no clear pattern of time correlation; different bands do not always rise and fall together, even in the optical, X-ray, and γ-ray bands. The spectra are modeled using a leptonic jet, with combined synchrotron self-Compton plus external Compton γ-ray production. Spectral variability of 3C 279 is consistent with variations of the bulk Lorentz factor of the jet, accompanied by changes in the spectral shape of the electron distribution. Our modeling results are consistent with the UV spectrum of 3C 279 being dominated by accretion disk radiation during times of low γ-ray intensity.

Day-Scale Variability of 3C?279 and Searches for Correlations in Gamma-Ray, X-Ray, and Optical Bands

Light curves of 3C 279 are presented in optical (R band), X-rays (RXTE/PCA), and γ rays (CGRO/EGRET) for 1999 January-February and 2000 January-March. During both of those epochs the γ-ray levels were high and all three observed bands demonstrated substantial variation, on timescales as short as 1 day. Correlation analyses provided no consistent pattern, although a rather significant optical/γ-ray correlation was seen in 1999, with a γ-ray lag of ~2.5 days, and there are other suggestions of correlations in the light curves. For comparison, correlation analysis is also presented for the γ-ray and X-ray light curves during the large γ ray flare in 1996 February and the two γ-bright weeks leading up to it; the correlation at that time was strong, with a γ-ray/X-ray offset of no more than 1 day.

Evidence of rapid optical variability in selected narrow-line Seyfert 1 galaxies

Abstract We present the first results of a search for the presence of rapid optical variability in a sample of five Narrow-Line Seyfert 1 galaxies. We find clear evidence of rapid variability for IRAS 13224-3809 with variations occurring on time scales of an hour. However, the results are less conclusive for the other four sources in our sample, Markarian 766, PG 1244+026, PG 1404+226 and Arakelian 564. While there are several instances among these latter objects where there is a hint that variability may be present, IRAS 13224-3809 provides the only conclusive evidence of rapid optical variability detected to date.

A photometric investigation of the optical variability of Markarian 501

The optical variability of the BL Lacertae object, Markarian 501, has been monitored from 1976–1987. Long-term optical variations have been detected with an amplitude of 0.65 mag. The long-term small amplitude, color variations which have been observed are found to be weakly correlated with the long-term trends in brightness in the sense that the object appears bluer when it is brighter. No evidence has been found for variability on a time scale of days or less for this object.