Long-term optical variability of the blazars PKS 2005-489 and PKS 2155-304

Abstract

We present optical light curves for the period 1996-2000, of two of the brightest known EGRET BL Lac objects: PKS 2005-489 and PKS 2155-304, the latter also one of the few known TeV sources. For both objects, quiescent epochs of low level of variability were followed by active periods, without any indication of periodicity. In PKS 2005-489, several variability events with duration of about 20 days were observed. In PKS 2155-304 fast drops and subsequent rises in luminosity occurred in time scales of days. We proposed an explanation in which a region moving along the relativistic jet is eclipsed by broad line region clouds or star clusters in the host galaxy. We compare our light curves with contemporaneous X-ray observations from All-Sky Monitor/RXTE. Correlations between optical and X-ray activity were not found in any of the sources at long time scales. However in PKS 2005-489 possible correlations were observed in 1997 and 1998 at short time scales, with optical variability preceding X-rays by 30 days in 1997 and succeeding them by about 10 days in 1998. The analysis of the SED, using the optical data presented here and BeppoSAX contemporaneous observations obtained from the literature, shows only small shifts in the synchrotron peak as the X-ray flux density changes.

arXiv comment23 pages,12 figures, accepted for publication in AJ

References in corpus (20)

• Unified Schemes for Radio-Loud Active Galactic Nuclei
• First Results from the All-Sky Monitor on the Rossi X-ray Timing Explorer
• BeppoSAX Observations of Unprecedented Synchrotron Activity in the BL Lac Object Mkn 501
• VHE Gamma Rays from PKS 2155-304
• The Parsec-Scale Structure and Jet Motions of the TeV Blazars 1ES 1959+650, PKS 2155-304, and 1ES 2344+514
• Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. III. Probing the Inner Jet through Multiwavelength Correlations
• Rapid X-ray Variability of the BL Lacertae Object PKS 2155-304
• Predicted Extragalactic TeV Gamma-Ray Sources
• Detection of Exceptional X-Ray Spectral Variability in the TeV BL Lac 1ES 2344+514
• Spectral Evolution of PKS 2155-304 observed with BeppoSAX during an Active Gamma-ray Phase
• A 5-GHz Southern Hemisphere VLBI Survey of Compact Radio Sources - II
• Modeling the variability of the BL Lacertae object PKS 2155-304
• Multiwavelength Monitoring of the BL Lacertae Object PKS 2155-304 in May 1994. I. The Ground-Based Campaign
• BeppoSAX Observations of 1 Jy BL Lacertae Objects. I
• X-Ray Spectral Variability of PKS 2005-489 During the Spectacular November 1998 Flare
• EGRET Spectral Index and the Low-Energy Peak Position in the Spectral Energy Distribution of EGRET-Detected Blazars
• Multiband optical polarimetry of the BL Lac object PKS 2155--304. Intranight and long term variability
• A Search for Intraday Variability in the Blazar PKS 2005-489
• The 0.1-200 keV spectrum of the blazar PKS 2005-489 during an active state
• Extension of Tycho catalog for low-extinction windows in the galactic bulge

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• CANGAROO-III Observations of the 2006 Outburst of PKS2155-304
• Optical monitoring in southern blazars. Analysis of variability and spectral colour behaviours
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