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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