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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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slide1
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)
slide11

- 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?

slide18

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?
slide19

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.
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