The Optical Microvariability of the        BL Lacertae Object S5 0716+714 and Its Multi-waveband Cor...
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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

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Outline 5123454

The Optical Microvariability of the BL Lacertae Object S5 0716+714 and Its Multi-waveband Correlations

Poon Helen

Beijing Normal University


Outline

Outline

  • Characteristics of Blazars

  • Introduction to Microvariability

  • Observation Details

  • Observation Results and Analysis

  • Multi-Waveband Correlations


Characteristics of blazars

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

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

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

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


S5 0716 714

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

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

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

Lightcurves(R band)


Outline 5123454

- 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-2008-12-24


Microvariability 2008 12 25

2008-12-25 BVRI

amplitude~ 0.09 mag

CMD

r = 0.150

Variation mechanism

external reason ?

geometric effect?

microvariability-2008-12-25


Summary

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

Multi-waveband Correlations

  • Importance:

    spectral energy distributions(SEDs), multiwavelength correlations  blazar physics  emission models

  • Method:

    simultaneous multiwavelength observations


Blazar models

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

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?


Outline 5123454

  • 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?


Outline 5123454

  • 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


Summary1

Summary

  • Different models at different times and states

  • Simultaneous observation necessary to understand the physics and constrain models.


Thank you

Thank you


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