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VLBA Imaging of the γ -ray Emission Regions in Blazar Jets. or: A Sequence of Images is Worth 1000 Light Curves Alan Marscher Boston University Research Web Page: www.bu.edu/blazars. Main Collaborators in the Study. Svetlana Jorstad, Iván Agudo, & M. Joshi (Boston University) - PowerPoint PPT Presentation
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VLBA Imaging of the γ-ray Emission Regions in Blazar Jets
or: A Sequence of Images is Worth 1000 Light Curves
Alan MarscherBoston University
Research Web Page: www.bu.edu/blazars
Main Collaborators in the Study
Svetlana Jorstad, Iván Agudo, & M. Joshi (Boston University)
Valeri Larionov (St. Petersburg State U., Russia)
Margo & Hugh Aller (U. Michigan) Paul Smith (Steward Obs.)
Anne Lähteenmäki (Metsähovi Radio Obs.)
Mark Gurwell (CfA) Ann Wehrle (SSI) Paul Smith (Steward)
Thomas Krichbaum (MPIfR) + many others
Telescopes: VLBA, GMVA, EVLA, Fermi, RXTE, Swift, Herschel,
IRAM, UMRAO, Lowell Obs., Crimean Astrophys. Obs., St.
Petersburg U., Pulkovo Obs., Abastumani Obs., Calar Alto
Obs., Steward Obs., + many othersFunded by NASA & NSF
Svetlana Jorstad, Iván Agudo, & M. Joshi (Boston University)
Valeri Larionov (St. Petersburg State U., Russia)
Margo & Hugh Aller (U. Michigan) Paul Smith (Steward Obs.)
Anne Lähteenmäki (Metsähovi Radio Obs.)
Mark Gurwell (CfA) Ann Wehrle (SSI) Paul Smith (Steward)
Thomas Krichbaum (MPIfR) + many others
Telescopes: VLBA, GMVA, EVLA, Fermi, RXTE, Swift, Herschel,
IRAM, UMRAO, Lowell Obs., Crimean Astrophys. Obs., St.
Petersburg U., Pulkovo Obs., Abastumani Obs., Calar Alto
Obs., Steward Obs., + many othersFunded by NASA & NSF
Diagram of a Quasar
Gamma-ray emission might occur inside BLR, in 7 mm core, or elsewhere along the jet via scattering of different sources of seed photons by relativistic electrons in the jet
Method for Locating High-frequency Emission
• mm-wave VLBI imaging to follow changes in jet, especially motions of superluminal knots
• Associate optical, X-ray, or -ray flares with superluminal knot if flare is coincident with passage of knot through 43 GHz “core” (which is parsecs downstream of black hole)
• Measure optical polarization position angle during flare & match with VLBI feature with similar value of
• Determine location of X-ray & gamma-ray emission sites by time lag of high-E variations relative to changes in optical & mm-wave flux or when knot is in core
• mm-wave VLBI imaging to follow changes in jet, especially motions of superluminal knots
• Associate optical, X-ray, or -ray flares with superluminal knot if flare is coincident with passage of knot through 43 GHz “core” (which is parsecs downstream of black hole)
• Measure optical polarization position angle during flare & match with VLBI feature with similar value of
• Determine location of X-ray & gamma-ray emission sites by time lag of high-E variations relative to changes in optical & mm-wave flux or when knot is in core
Time when knot passes through core
Quasar PKS 1510-089 (z=0.361) in 2009
Multiwaveband monitoring: General (but not one-to-one) correspondence between -ray & optical
37 GHz flux starts rising at same time as start of -ray/optical outburst
Marscher et al. (2010, Astrophysical Journal Letters, 710, L126)2009.0 2009.6
VLBA images at 43 GHz
Bright superluminal knot passed “core” at time of extreme optical/-ray flare
Apparent speed = 21c
Color: linearly polarized intenisty Contours: total intensity
Rotation of Optical Polarization in PKS 1510-089Rotation starts when major optical activity
begins, ends when major optical activity ends & centroid of superluminal blob passes through core
2009.0 2009.6
Model curve: blob following a spiral path in an accelerating flow
increases from 8 to 24, from 15 to 38Blob moves 0.3 pc/day as it nears core
Core lies > 17 pc from central engine
- After rotation, optical pol. angle ~ same as that of superluminal knot
- Also, later polarization rotation similar to end of earlier rotation, as expected if caused by geometry of B; event occurs as a weaker blob approaches core
Sites of -ray Flares in PKS 1510-089
Interpretation:
All flares in early 2009 caused by a single superluminal knot moving down jet
Sharp flares occur as knot passes regions of high photon density or standing shocks that compress the flow or energize high-E electrons
Sites of high optical/IR emission in relatively slow sheath of jet
Standing shock system, “core”
Knot
Broad-line clouds
Flu
x 2. X-ray dominant flare, peak after new knot appears
3C 279 in 2008-091. Multi-flare outburst in -ray, optical, & X-ray after new superluminal knot appears
knot
3. Simultaneous -ray, optical, & X-ray flare near time when superluminal knot appears
3C 454.3: Outbursts seen first at mm wavelengths
3C 454.3: 2010 super-outburst3C 454.3: 2010 super-outburst
RJD=5502, 1 Nov 2010; core: 10.3 Jy
RJD=5507, 6 Nov 2010; core: 14.1 Jy
RJD=5513, 12 Nov 2010; core: 14.2 Jy
RJD=5535, 4 Dec 2010; core: 17.7 Jy
Knot ejected in late 2009, vapp = 10c
OJ287 (Agudo et al. 2011, ApJL, 726, L13)
Change in jet direction starting ~ 2005
Core is the more southern compact feature, C0
High-E flare near start of mm-wave flux outburst & ~ coincident with max. in polarization of feature C1, which moves very slowly
Flare B appear to occur as superluminal knot passes through C1
Implications• Many gamma-ray flares in blazars occur in superluminal knots
that move down the jet & are seen in VLBA images⇒ Sometimes upstream of 43 GHz core⇒ Often in or downstream of 43 GHz core
• Intra-day γ-ray/optical variability can occur in mm-wave regions⇒ The highest-Γ jets are very narrow, < 1°, so at 10 pc from the
central engine, jet < 6 lt-months across⇒ Doppler factors can be very high, >50 (Jorstad et al. 2005)⇒ Volume filling factor of γ-ray/optical emission << 1 if very high-
energy electrons are difficult to accelerate (as in turbulent jet model of Marscher & Jorstad 2010)
• Rotations of polarization & timing of flares agree with magnetic-launching models of jets, where jet flow accelerates over long distances
Advantage of Wider Bandwidth/Higher Recording RateCurrently: High dynamic range (> 100:1) at 43
GHz if core flux > ~0.5 Jy Low sensitivity/dynamic range at 86
GHz Cannot image knots in key TeV
blazars such as Mkn 421 with high enough fidelity to measure motion
With upgrade (this year!):
Bandwidth for routine observations ~ 4 times broader
High sensitivity higher dynamic range
Mkn 421
1 Aug 2010
24 Oct 2010
4 Dec 2010
EXTRA SLIDES FOLLOW
Movie of the Quasar 3C 273 (z=0.158) [Director: S. Jorstad]
Emission feature following spiral path down jet - rotationn of EVPA
Feature covers much of jet cross-section, but not all
Centroid is off-center
Net B rotates as feature moves down jet, P perpendicular to B
Emission feature following spiral path down jet
P vector
Bnet
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