The Optical Microvariability of the BL Lacertae Object S5 0716+714 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 timescalesestimation of the size of the emission region R ≤ cΔt

• spectral changes and shape of lightcurves

different radiation and light variation mechanisms

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

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

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

Lightcurves （ R band ）

• 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

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

microvariability-2008-12-24

• 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-2008-12-25• 2008-12-25 BVRI• amplitude ~ 0.09 mag• CMD

r = 0.150• Variation mechanism

external reason ？ geometric effect ？

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

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 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?

• 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.

Thank you