outline
Post on 09-Jan-2016
17 Views
Preview:
DESCRIPTION
TRANSCRIPT
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
top related