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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
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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 others Funded 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 others Funded by NASA & NSF
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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
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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
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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) 2009.02009.6 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
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Rotation of Optical Polarization in PKS 1510-089 Rotation starts when major optical activity begins, ends when major optical activity ends & centroid of superluminal blob passes through core 2009.02009.6 Model curve: blob following a spiral path in an accelerating flow increases from 8 to 24, from 15 to 38 Blob 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
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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
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Flux 2. X-ray dominant flare, peak after new knot appears 3C 279 in 2008-09 1. 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
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3C 454.3: Outbursts seen first at mm wavelengths
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3C 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, v app = 10c
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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
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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
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Advantage of Wider Bandwidth/Higher Recording Rate Currently: 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
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EXTRA SLIDES FOLLOW
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Movie of the Quasar 3C 273 (z=0.158) [Director: S. Jorstad]
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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 B net 1 2 3 4
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