1. Is the Inner Radio Jet of BL Lac Precessing? R. L. Mutel University of Iowa Astrophysics Seminar 17 September 2003

2. 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

3. UI Astrophysics Seminar Sept 2003 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

4. UI Astrophysics Seminar Sept 2003 S10 apparent speed 1998-7 -2001.4

5. UI Astrophysics Seminar Sept 2003 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 N Core S Core (high RM) S11 (low RM) S10 (low RM) Note: hint of gradient

6. UI Astrophysics Seminar Sept 2003 Note: low Core polarization (~2%) S9 only visible on PPOL map BL Lac Sept 99 at 15, 22, 43GHz IPOL, PPOL, FPOL maps S9 Core Pol’n ~5% Core contains emerging component

7. UI Astrophysics Seminar Sept 2003 Core, S10 Rotation measure vs. Epoch S10 Core 1998.97 S10

8. UI Astrophysics Seminar Sept 2003 Core depolarization modeled with random scattering screen Core fractional polarization is approximately quadratic with wavelength

9. UI Astrophysics Seminar Sept 2003 Foreground turbulent Rotation Measure screen Assume quadratic structure function of RM fluctuations (Tribble 1991) Fractional polarization vs. wavelength Best-fit values:

10. UI Astrophysics Seminar Sept 2003 Evidence for sheath boundary layer (parallel magnetic field)

11. UI Astrophysics Seminar Sept 2003 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?

12. UI Astrophysics Seminar Sept 2003 Earth-Moon-Sun system

13. UI Astrophysics Seminar Sept 2003 SS433 Precession period 164 days Companion Wolf-Rayet star (?) Ballistic jets at v = 0.25c Associated with SN remnant (W50)

14. UI Astrophysics Seminar Sept 2003

15. 4C12.50 (Lister et al 2003 astro-ph) 200 pc

16. UI Astrophysics Seminar Sept 2003 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

17. UI Astrophysics Seminar Sept 2003 Stirling et al. 1mm JCMT Observations

18. UI Astrophysics Seminar Sept 2003 Stirling et al 43 GHz radio map: Periodic change in ‘structural position angle between C1, C2

19. UI Astrophysics Seminar Sept 2003 Our SPA Observations, and comparison to Stirling et al. Our data, constant model  2 = 0.83 Our data with best-fit model (solid,  2 = 0.58 ), Stirling model (dashed) Combined SPA data with Stirling model

20. UI Astrophysics Seminar Sept 2003 Model fit results

21. UI Astrophysics Seminar Sept 2003 Possible problems with precession period: 1.Companion hypothesis (binary BH): A. Binary black hole Assume 2 BH equal mass (M bh ~ 3 10 8 M sun,, P = 2.3 yr) a = 10 3 AU (200 Rs) B. Gravitational radiation : L GR ~ 10 40 W (1% L rad !) Timescale for coalescence: This seems implausibly short

22. UI Astrophysics Seminar Sept 2003 Precession issues continued Warped accretion disk: Lense-Thirring precession from warped accretion disk? (Bardeen & Petterson 1975; Scheuer 1992) 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 R 3 )

23. UI Astrophysics Seminar Sept 2003 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