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Is the Inner Radio Jet of BL Lac Precessing?

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

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Is the Inner Radio Jet of BL Lac Precessing?

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

  2. 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 BL Lac VLBP monitoring log UI Astrophysics Seminar Sept 2003

  3. Superluminal Component S10 1998.7 -2001.6: Trajectory fits helical model 98.7- 99.2 S10 N.B. Not ballistic Model line predicted by Denn et al. 2000 00.4-01.6 Helical model (Hardee 1987) using adiabatic expansion of light jet, LOS angle 5º ± 1º (forward shock) UI Astrophysics Seminar Sept 2003

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

  5. Bl Lac May 1999 PPOL maps1. Core, component EVPA structure at high frequencies2. Low Rotation measure in jet, vs. high RM of core Core (high RM) Core N Core S S11 (low RM) Note: hint of gradient S10 (low RM) 22 GHz 15 GHz 43 GHz UI Astrophysics Seminar Sept 2003

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

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

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

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

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

  11. 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? UI Astrophysics Seminar Sept 2003

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

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

  14. UI Astrophysics Seminar Sept 2003

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

  16. 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 Is the jet nozzle of BL Precessing? UI Astrophysics Seminar Sept 2003

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

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

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

  20. Model fit results UI Astrophysics Seminar Sept 2003

  21. 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: Possible problems with precession period: This seems implausibly short UI Astrophysics Seminar Sept 2003

  22. 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 R3) UI Astrophysics Seminar Sept 2003

  23. 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 Summary UI Astrophysics Seminar Sept 2003

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