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Optical Microvariability of BL Lac Object S5.0716+714 and Multi-waveband Correlations

This paper discusses the characteristics of blazars, microvariability, and the observation results and analysis of BL Lac object S5.0716+714. It explores the multi-waveband correlations and different variability timescales, as well as the importance of studying microvariability in estimating the size of the emission region and understanding different radiation mechanisms.

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Optical Microvariability of BL Lac Object S5.0716+714 and Multi-waveband Correlations

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  1. The Optical Microvariability of the BL Lacertae Object S5 0716+714 and Its Multi-waveband Correlations Poon Helen Beijing Normal University

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

  3. 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

  4. 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

  5. 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

  6. 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

  7. S5 0716+714 • BL Lac object • ra：07:21:53.447 dec：+71:20:36.35 (2000) • highly active(duty cycle~ 1) • magnitude: R ~ 12-15 mag • spectral changes - bluer-when-brighter - no spectral change - redder-when-brighter

  8. Observation Details • Telescope used：Xinglong 85 cm reflector Camera:PI 1024 BFT，1024 x 1024 pixels FOV:16’.5 x 16’.5 • Observation Period：25-30 Oct, 2008 23-29 Dec, 2008 3-10 Feb, 2009 • Valid data: 14 days • Filters used: BVRI

  9. Data Reduction • Bias, dark, flat correction • IRAF apphot package • comp：star 5 （Villata et al.(1998)） check：star 6 • flux calibration • photometric error ~ 0.003 – 0.015

  10. Amplitude ~ 0.4mag（1st） ~ 0.5mag（2nd） ~ 0.8mag（3rd） outburst 1st：JD 2454766 R ∼ 13. 01 mag 2nd：JD 2454825 R ∼ 13.16 mag 3rd: JD 2454825 R ∼ 13.16 mag 4th：JD 2454867 R ∼ 12. 95 mag Lightcurves（R band）

  11. - microvariability: 13/14 days (C > 2.576) - Amplitude (R band) ~0.004 – 0.28 mag - R ~ 12.95 – 13.64 mag

  12. 2008-12-24 VRI amplitude~ 0.14mag Color-magnitude diagram r(Pearson correlation coefficient) = 0.618 Bluer when brighter Variation mechanism internal reason? shock-in-jet model? microvariability-2008-12-24

  13. 2008-12-25 BVRI amplitude~ 0.09 mag CMD r = 0.150 Variation mechanism external reason ？ geometric effect？ microvariability-2008-12-25

  14. Summary • Very active during observation, 4 outbursts observed • Microvariability observed:13 out of 14 days • Microvariability amplitude~ 0.004 – 0.28 mag • BWB  shock-in-jet model； no spectral change geometric effect

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

  16. 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)

  17. SED of S5 0716+714 • 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?

  18. 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?

  19. 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

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

  21. Thank you

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