The Optical Microvariability of the BL Lacertae Object S and Its Multi-waveband Correlations Poon Helen Beijing Normal University

Outline Characteristics of Blazars Introduction to Microvariability Observation Details Observation Results and Analysis Multi-Waveband Correlations

Characteristics of Blazars Highly Variable and polarized Jet <10°(unified model of AGN) Different Variability Timescales Subclasses - BL Lac Objects: weak/no emission lines in spectrum - Flat Spectrum Radio Quasars ： clear emission lines in spectrum

Introduction to Microvariability microvariability/intranight optical variability,INOV first discovered in the 60s （ Matthews & Sandage (1963) ） Coverage of microvariability of BL Lac objects ~ 80%(Heidt & Wagner (1996)) Spectral changes - bluer-when-brighter(BWB) - redder-when-brigher (RWB) - no spectral change

Reasons for Microvariability external reasons ： -interstellar scintillation -microlensing -geometric effect (lighthouse effect)  no spectral change internal reasons ： -shock-in-jet model -perturbations of accretion disk  spectral changes

Importance of Studying Microvariability shortest timescales  estimation of the size of the emission region R ≤ cΔt spectral changes and shape of lightcurves  different radiation and light variation mechanisms

S BL Lac object ra ： 07:21: dec ： +71:20:36.35 (2000) highly active (duty cycle ~ 1) magnitude : R ~ mag spectral changes - bluer-when-brighter - no spectral change - redder-when-brighter

Observation Details Telescope used ： Xinglong 85 cm reflector Camera:PI 1024 BFT ， 1024 x 1024 pixels FOV:16’.5 x 16’.5 Observation Period ： Oct, Dec, Feb, 2009 Valid data: 14 days Filters used: BVRI

Data Reduction Bias, dark, flat correction IRAF apphot package comp ： star 5 （ Villata et al.(1998) ） check ： star 6 flux calibration photometric error ~ – 0.015

Lightcurves （ R band ） Amplitude ~ 0.4mag （ 1st ） ~ 0.5mag （ 2nd ） ~ 0.8mag （ 3rd ） outburst 1st ： JD R ∼ mag 2 nd ： JD R ∼ mag 3rd: JD R ∼ mag 4th ： JD R ∼ mag

- microvariability: 13/14 days (C > 2.576) - Amplitude (R band) ~0.004 – 0.28 mag - R ~ – mag

microvariability VRI amplitude ~ 0.14mag Color-magnitude diagram r(Pearson correlation coefficient) = Bluer when brighter Variation mechanism internal reason? shock-in-jet model?

microvariability BVRI amplitude ~ 0.09 mag CMD r = Variation mechanism external reason ？ geometric effect ？

Summary Very active during observation, 4 outbursts observed Microvariability observed: 13 out of 14 days Microvariability amplitude ~ – 0.28 mag BWB  shock-in-jet model ； no spectral change  geometric effect

Multi-waveband Correlations Importance: spectral energy distributions(SEDs), multiwavelength correlations  blazar physics  emission models Method: simultaneous multiwavelength observations

Blazar Models Synchrotron Self Compton(SSC) model: - Gamma rays are produced by relativistic electrons via inverse Compton scattering of the synchrotron photons in the jet External Compton(EC) model: - IC scattering of photons originating outside the jet (e.g.accretion disk, broad line region, CMB)

SED of S Red (2008 April data) -Gray (historical data) -Solid line (one-zone SSC model) -Dashed line (spine-layer model) -From Anderhub et al. 2009, ApJ, 704, 129 -Source state: high flux both in the optical and gamma ray band - Better fit? SSC or spine- layer model?

From Tagliaferri et al., 2003, A&A, 400, 477 All data taken when the source was in a bright state Better fit? SSC only or SSC + EC model?

From Vittorini et al., 2009, ApJ, 7106, 1433 Modelling of SED of two flares One-component SSC model: simplest SSC model Two-component SSC model: one component for slowly variable raido and hard X-ray bands and the other for faster variable optical, soft X- and γ- ray bands

Summary Different models at different times and states Simultaneous observation necessary to understand the physics and constrain models.

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