is the inner radio jet of bl lac precessing?

Is the Inner Radio Jet of BL Lac Precessing?

R. L. Mutel

University of IowaAstrophysics Seminar

17 September 2003

UI Astrophysics Seminar Sept 2003

BL Lac VLBP monitoring log

• 9 epochs from 1998.7 – 2001.4

• 3-5 month separation between observations

• 15, 22, 43 GHz, VLBA, full polarization

• EVPA calibration using VLBA calibration Database


Superluminal Component S10 1998.7 -2001.6: Trajectory fits helical model

98.7- 99.2

00.4-01.6

Helical model (Hardee 1987) using adiabatic expansion of light jet, LOS angle 5º ± 1º (forward shock)

S10

Model line predicted by Denn et al. 2000

N.B. Not ballistic


S10 apparent speed

1998-7 -2001.4


Bl Lac May 1999 PPOL maps

1. Core, component EVPA structure at high frequencies

2. Low Rotation measure in jet, vs. high RM of core

15 GHz 22 GHz 43 GHz

Core NCore S

Core (high RM)

S11 (low RM)

S10 (low RM)

Note: hint of gradient


Note: low Core polarization (~2%)

S9 only visible on PPOL map

BL Lac Sept 99 at 15, 22, 43GHzIPOL, PPOL, FPOL maps

S9

Core Pol’n ~5%

Core contains emerging component


Core, S10 Rotation measure vs. Epoch

S10

Core

1998.97

S10


Core depolarization modeled with random scattering screen

Core fractional polarization is approximately quadratic with wavelength


Foreground turbulent Rotation Measure screen

Assume quadratic structure function of RM fluctuations (Tribble 1991)

2

0RM

sD s

s

Fractional polarization vs. wavelength

3/ 2 2( )

2

os

tp

Best-fit values:2

0

4000

0.03

rad m

s AU

:

:


Evidence for sheath boundary layer (parallel magnetic field)


Cf. Blazar 1055+018 (1997.0, 5 GHz) (Attridge et al. 1999)

B vectors

If these are sheaths (jet-ambient medium interaction regions) with (cold?) entrained material, why is the synchrotron emissivity so

high?

Perhaps due to helical structure of B field itself?


Earth-Moon-Sun system

dLL

dt

orbprec orb

spin

I

I

1~300earth

I

I

1~30

orb

spin earth moon

13~10 ~ 25,000 yprec precP


SS433• Precession period 164 days

• Companion Wolf-Rayet star (?)

• Ballistic jets at v = 0.25c

• Associated with SN remnant (W50)

•


4C12.50 (Lister et al 2003 astro-ph)

200

pc


Is the jet nozzle of BL Precessing?

• Precession: physics summary• Examples

– Earth-Moon-Sun system (companion torque)– Galactic jets: SS433 (companion torque)– Extragalactic Jets: 4C12.50 (Accretion disk torque?)

• Evidence for BL Lac Precession (Stirling et al. MNRAS 2003)

• Independent test (Mutel et al. 2003)• Possible problems with precession

– Binary hypothesis: Gravitational radiation timescale– Accretion disk precession: Lens-Thirring timescale


Stirling et al. 1mm JCMT Observations


Stirling et al 43 GHz radio map: Periodic change in ‘structural

position angle between C1, C2


Our SPA Observations, and comparison to Stirling et al.

Our data, constant model 2 = 0.83Our data with best-fit model

(solid, 2 = 0.58), Stirling model (dashed)

Combined SPA data with Stirling model


Model fit results


Possible problems with precession period:

1. Companion hypothesis (binary BH): A. Binary black hole

Assume 2 BH equal mass (Mbh ~ 3 •108 Msun, , P = 2.3 yr)

a = 103 AU (200 Rs)B. Gravitational radiation:

LGR ~ 1040 W (1% Lrad!)

Timescale for coalescence:3 2

55 4

9610

5

P G Myrs

P c a

&

This seems implausibly short


Precession issues continued

• Warped accretion disk: Lense-Thirring precession from warped accretion disk? (Bardeen & Petterson 1975; Scheuer 1992)

3

max

2LTs s

R c J

R R J

P ~ few years is only possible with maximally rotating BH with accretion disk of radius r ~ 10 AU (~20 Rs) (much longer for larger R, scales as R3)


Summary• Superluminal component S10 position, speed consistent with

prediction of helical model described in Denn et al. 2000 (ApJS).

• All jet components have B field orientation within 20º of to jet direction (consistent with perpendicular shocks, < 1), low RM (-300 ± 300 rad-m-2)

• Core rotation measure high (RM~2000 rad-m-2), probably variable (but very difficult to isolate from emerging components)

• Core depolarization vs. wavelength can be modeled with random RM fluctuating screen, s~ 0.3 AU, σ~ 4000 rad-m-2

• Strong evidence for weak sheath component with parallel magnetic field [at least 3 epochs]

• 43 GHz maps do not agree with 2-yr core precession claim of Stirling et al. 2003

is the inner radio jet of bl lac precessing?

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