Optical Variability of Optical Variability of BL Lac Object OJ 287BL Lac Object OJ 287

Wu JianghuaWu Jianghua2005.82005.8

Properties of BlazarsProperties of Blazars

A subset of AGNs;A subset of AGNs; Rapid and strong variation Rapid and strong variation

without evident period;without evident period; High polarization, highly High polarization, highly

variable;variable; Power-law optical Power-law optical

continuum;continuum; Radio-loud, flat-spectrum;Radio-loud, flat-spectrum; Superluminal motion.Superluminal motion.

BL Lac (no emission line)BL Lac (no emission line)FSRQ (emission line)FSRQ (emission line)

Historical Light Curve of OJ 287Historical Light Curve of OJ 287

the only blazar with convincing evidence of periodic light curve

The OJ-94 ProjectThe OJ-94 Projecthttp://www.astro.utu.fi/oj94/http://www.astro.utu.fi/oj94/

Sillanpaa et al. (1988) predicted a new outbursSillanpaa et al. (1988) predicted a new outburst in 1994-96 from the historical light curves;t in 1994-96 from the historical light curves;

The OJ-94 project was organized (Takalo et al. The OJ-94 project was organized (Takalo et al. 1996);1996);

More than 50 astronomers from 10 countries;More than 50 astronomers from 10 countries; From radio, infrared, optical, UV, to X-ray;From radio, infrared, optical, UV, to X-ray; Time span: 1993Time span: 19931997.1997.

Optical Results of OJ-94Optical Results of OJ-94

Double-peaked structure

Color Behavior During OutburstColor Behavior During Outburst

Based on the observations of the 94-96 outburst

Properties of the Light CurvesProperties of the Light Curves

12-year cyclic optical outburst;12-year cyclic optical outburst;

Double-peaked structure of the outburst;Double-peaked structure of the outburst;

The first peak is narrow and thermal while the The first peak is narrow and thermal while the

second is broad and synchrotronic.second is broad and synchrotronic.

Extremely stable color during the outburst;Extremely stable color during the outburst;

Models for Cyclic OutburstsModels for Cyclic Outbursts

Binary black hole models (Sillanpaa et al. 198Binary black hole models (Sillanpaa et al. 1988; Lehto & Valtonen 1996; Valtaoja et al. 2008; Lehto & Valtonen 1996; Valtaoja et al. 2000; Liu & Wu 2002);0; Liu & Wu 2002);

Beaming model (Villata et al. 1996; 1998);Beaming model (Villata et al. 1996; 1998); Precessing disc model (Katz 1996);Precessing disc model (Katz 1996); Microlensing effect;Microlensing effect; Lighthouse effect;Lighthouse effect;

Our Monitoring ProgramOur Monitoring Program

Time span (JD 2453400 Time span (JD 2453400 2453489); 2453489);

Actual 26 nights;Actual 26 nights; Filter (BATC e, i, m);Filter (BATC e, i, m); Exposure time Exposure time (180 (180 300 s). 300 s).

~ R ~ I

The Finding ChartThe Finding Chart

Nightly Mean Light CurveNightly Mean Light Curve

Amplitude: ~ 1 mag

Color BehaviorColor Behavior

A weak bluer-when-brighter trend

Structure Function AnalysisStructure Function Analysis

a period of ~ 40 days

The 94-peak RevisitedThe 94-peak Revisited

SF Analysis of the 94-peakSF Analysis of the 94-peak

a period of ~ 40 days, consistent with our monitoring results

ConclusionsConclusions The variation of OJ 287 shows a period of ~ 40 days The variation of OJ 287 shows a period of ~ 40 days

in its quiescent state; in its quiescent state; The variation of OJ 287 during the 1994-peak can be The variation of OJ 287 during the 1994-peak can be

resolved into two components: The first component resolved into two components: The first component can be considered as the continuing of the normal can be considered as the continuing of the normal blazar variation. It has the similar amplitude and blazar variation. It has the similar amplitude and timescale as those in quiescent state; The second timescale as those in quiescent state; The second component can be taken as a ‘low-frequency’ component can be taken as a ‘low-frequency’ modulation of the first component. It may be induced modulation of the first component. It may be induced by the BBH interaction.by the BBH interaction.

Constraints on the model of the outbursts…Constraints on the model of the outbursts…

Future Monitoring with New FacilitiesFuture Monitoring with New Facilities

Interference filter with multi-peaks + objective Interference filter with multi-peaks + objective prism + Schmidt telescopeprism + Schmidt telescope

Make photometric measurements exactly Make photometric measurements exactly simultaneously in multi-wavebandssimultaneously in multi-wavebands

Use timescale and color behavior of the Use timescale and color behavior of the variation to constrain the mechanisms of the variation to constrain the mechanisms of the variabilityvariability

Interference filter with multi-peaksInterference filter with multi-peaks

Light Path DiagramLight Path Diagram

Test ObservationsTest Observations

Thanks!Thanks!