Polarization Swings Reveal Magnetic Energy Dissipation in Blazars

Transcription

1 Polarization Swings Reveal Magnetic Energy Dissipation in Blazars Xuhui Chen Most of this work is done by : Haocheng Zhang (Ohio University & LANL, USA) Other Collaborators: Markus Boettcher (North-West Uni., South Africa ) Fan Guo & Hui Li (LANL, USA) Polarization and Active Galactic Nuclei , Strasbourg

2 Blazar emission Synchrotron emission νfν ν (Urry & Padovani, 1995) Abundant radiation from the disk, torus, and BLR Blazar jets Relativistic jets with Γ>10, observed from small angle

3 Optical Polarization Angle Swing Polarization degree varies between 2% and 35%, and correlates with flux Rotation of polarization angle by 720 PKS (Marscher et al. 2010) 3

4 More Polarization Angle Swing Step-wise rotation of polarization angle S (Ikejiri et al. 2011) 4

5 Previously Proposed Interpretations: Helical magnetic fields in a curved jet (Abdo et al. 2010) Helical streamlines, guided by a helical magnetic field (Villata & Raiteri 1999) Turbulent Extreme Multi-Zone Model (Marscher 2014)

6 Synchrotron Polarization in an axisymmetric jet Model Viewing direction in comoving frame: θobs ~ π/2 Helical B (Chen et al. 2014) Viewing direction in obs. Frame: θobs ~ 1/Γ

7 Perturbation propagates Light Travel Time Effects B B B (Zhang et al. 2015) Shock positions at equal photon-arrival times at the observer

8 Flaring Scenario: Magnetic-Field Compression perpendicular to shock normal Baseline parameters based on SED and light curve fit to PKS (Chen et al. 2012)

9 Flaring Scenario: Magnetic-Field Compression perpendicular to shock normal vs. time Synchrotron + Accretion Disk SEDs Frequency-dependent Polarization angle vs. time PKS (Zhang et al. 2015)

10 Flaring Scenario: Stronger B compression Synchrotron + Accretion Disk SEDs vs. time Frequency-dependent Polarization angle vs. time PKS (Zhang et al. 2014)

11 Flaring Scenario: Increase of particle acceleration Polarization angle vs. time PKS (Zhang et al. 2014)

12 Application to the FSRQ 3C279 Simultaneous optical + γ-ray flare, correlated with a 180o polarizationangle rotation. (Abdo et al. 2010) Polarization Degree Polarization Angle

13 Application to 3C279 Simultaneous fit to SEDs, light curves, polarization-degree and polarization-angle swing SED Fermi Lightcurve PD % vs. time R-Band Lightcurve EVPA vs. time (Zhang et al. 2015)

14 Constraint in 3C279 Requires particle acceleration and reduction of magnetic field, as expected in magnetic reconnection! SED Fermi Lightcurve PD % vs. time R-Band Lightcurve EVPA vs. time (Zhang et al. 2015)

15 Summary Helical magnetic field and light-travel-time effect causes Synchrotron polarization swings of >= 180º without requirement of nonaxisymmetric jet features! Polarization swings can appear very different in each case, based on the parameters, geometry, and flaring scenarios. Simultaneous fit to SEDs, lightcurves, polarization degree and polarization-angle swing of 3C279 requires magnetic energy dissipation.

16 Reference Urry & Padovani, PASP, 107, 803 Abdo et al. 2010, Nature, 463, 919 Ikejiri et al. 2011, PASJ, 63, 639 Villata & Raiteri, 1999, A&A, 347, 30 Marscher et al. 2010, ApJL, 710, 126 Chen et al. 2012, MNRAS, 424, 789 Chen et al. 2014, MNRAS, 442, 2188 Zhang et al. 2014, ApJ, 789, 66 Zhang et al. 2015, ApJ, 804, 58

17 Flaring Scenario: Z>2R, B compression vs. time Synchrotron + Accretion Disk SEDs Frequency-dependent Polarization angle vs. time PKS (Zhang et al. 2015)

18 Flaring Scenario: Z>2R, increase of acceleration vs. time Synchrotron + Accretion Disk SEDs Frequency-dependent Polarization angle vs. time PKS (Zhang et al. 2015)

19 Flaring Scenario: Perturbation only in the center, B compression vs. time Synchrotron + Accretion Disk SEDs Frequency-dependent Polarization angle vs. time PKS (Zhang et al. 2015)