G. de Francesco

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.

The 65 Day Period in 3C 66A during Bright State

Historically, 3C 66A has been considered a relative quiescent blazar. For that reason, 3C 66A was selected as a comparison source for OJ 287 in the OJ-94 project. However, after more detailed observation it turns out that the variability of 3C 66A itself is very interesting. We have analyzed the entire project data set of 3C 66A from fall of 1993 to spring of 1998 by using structure function analysis, Deeming periodograms, Scargle periodograms, and the folded light curves. Here we present the first preliminary evidence for the 65 day period in 3C 66A observed during the bright state. Our analysis indicates that this period is slowly slowing down. We will also discuss the possible physical mechanism producing the observed periodicity.

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.

Measuring supermassive black holes with gas kinematics: the active S0 galaxy NGC 3998

Context. We present results from a kinematical study of the gas in the n ucleus of the active S0 galaxy NGC 3998 obtained from archival HST/STIS long-slit spectra. Aims. We analyzed the emission lines profiles and derived the map of the gas velocity field. The observed velocity curves are cons istent with gas in regular rotation around the galaxy’s center. Methods. By modeling the surface brightness distribution and rotati n curve of the Hα emission line we found that the observed kinematics of the circumnuclear gas can be accurately repro duced by adding to the stellar mass component a compact dark m ss (black hole) ofMBH = 2.7+2.4 −2.0×10 M⊙ (uncertainties at a 2 σ level); the radius of its sphere of influence ( Rsph∼ 0. 16) is well resolved at the HST resolution. Results. The BH mass estimate in NGC 3998 is in good agreement with both the MBH − Mbul (with an upward scatter by a factor of ∼ 2) andMBH −σ correlations (with a downward scatter by a factor of ∼ 3− 7, depending on the form adopted for the dependence of MBH onσ). Conclusions. Although NGC 3998 cannot be considered as an outlier, its loc ati n with respect to theMBH − σ relation conforms with the trend suggesting the presence of a connection betwe en th residualsfrom theMBH − σ correlation and the galaxy’s e ff ctive radius. In fact, NGC 3998 has one of the smallest values of Re among the galaxies with measured MBH (0.85 kpc) and it shows a negative residual. This suggests that a combination of both σ andRe is necessary to drive the correlations between MBH and other bulge properties, an indication for the presence of a black h oles “fundamental plane”.

Measuring supermassive black holes with gas kinematics - II. The LINERs IC 989, NGC 5077, and NGC 6500

We present results from a kinematical study of the gas in the nucleus of a sample of three LINER galaxies, obtained from archival HST/STIS long-slit spectra. We found that, while for the elliptical galaxy NGC 5077, the observed velocity curves are consistent with gas in regular rotation around the galaxys center, this is not the case for the two remaining objects. By modeling the surface brightness distribution and rotation curve from the emission lines in NGC 5077, we found that the observed kinematics of the circumnuclear gas can be accurately reproduced by adding to the stellar mass component a black hole mass of

Radio to γ-ray observations of 3C 454.3:1993–1995

M_{\rm BH} = 6.8_{-2.8}^{+4.3}\times 10^8~M_{\odot}

BeppoSAX observations of PKS 0528+134

(uncertainties at a 1 σ level); the radius of its sphere of influence (

Variability Characteristics of Blazar OJ 287

R_{\rm sph} \sim 0\farcs34

Optical photometric monitoring of γ-ray loud blazars. - I. Observations from November 1994 to November 1995

) is well-resolved at the HST resolution. The BH mass estimate in NGC 5077 is in fairly good agreement with both the

OPTICAL PHOTOMETRIC MONITORING OF GAMMA -RAY LOUD BLAZARS. II. OBSERVATIONS FROM NOVEMBER 1995 TO JUNE 1996

M_{\rm BH}-M_{\rm bul}