1. Magnetic Fields in Supernova Remnants Kashi & Urumqi, 2005 Sept. 7 th -14 th

2. SNRs, some historical Comments Synchrotron emission predicted by Alvén, Herlofson, Kiepenheuer First detected as optical emission from the Crab nebula 1953 Optical linear polarization discovered (Dombrovsky 1954) Radio polarization from the Crab detected, (Mayer et al. 1957) On Jisi day, the 7 th day of the month, a big new star appeared near the Ho star (China, 14 th century B.C.)

3. Evolution of SNRs (based on Woltjer 1972) log Radius log Time R  t R  t 2/5 R  t 2/7 R  t 1/4 Free Expansion Adiabatic Radiation Radiation Sedov internal pressure momentum merging into the interstellar medium

4. Magnetic Field and Evolution of SNRs Magnetic pressure number R H = magnetic pressure = B 0 2 /8   476 B 0 2 (mGs). dynamic pressure 1/2  0 v s 2 n 0 (cm - 3 )v s 2 (100km/s) 100 10 1 0.1 0.01 R H 10  Gs 100  Gs 1mGs 10mGs B0B0 10 -8 dyne cm -2 10 -7 dyne cm -2

5. Magnetic Field and Heat Conduction The evaporation of clouds depends on heat conduction dQ/dt = K gradT. For a typical cloud Q K > 10 ⁸,  the low magnetic heat conduction reduces the evaporation significantly. The cloud may survive, a star may be born. Q K = K thermal  10 5 T(K) 3 B(G) 2 K gyro n(cm -3 )

6. Observation of Magnetic Fields Faraday rotation angle:  rot (rad) = RM(rad/m 2 ) (m) 2 Rotation measure: RM(rad/m 2 ) = 8.1  10 5  N(cm -3 ) B ‖ (G) dz(pc)

7.  (rad) =  0 (rad) + RM(rad/m 2 )  (m) 2 +n  G127.1+0.5 =11cm E-Vectors = 6cm

8. Ambiguity of Rotation Measure HB9 100-m-RT ++  (rad) = 0.2+114 (m) 2 6cm 11cm 21cm

9. Ambiguity of Rotation Measure HB9 100-m-RT ++  (rad) = 0.2+114 (m) 2 6cm 11cm 21cm

10. S147 6cm Urumqi 25m-RT TP + B-Field + Pulsar ( )

11. Types of SNRs Young shells, historical SNRs: Tycho, SN1006, Kepler Old shells, evolved SNRs: G127.1+0.5, G116.9+0.2, many others Filled centered SNRs, Pulsar powered: Crab nebular, 3C58, …. Combined SNRs

12. Young Shells Tycho 10.55 GHz TP +B-Field 100-m-RT

13. Fine structure at 15 arcsec scale (0.2 pc) VLA 5 GHz (Wood et al., 1992) Tycho’s SNR

14. Young Shells Predominantly radial field Small scale variations (sub-pc scales) Polarized fraction (PI/TP) 4 to 15% with local enhancements. A large fraction of random magnetic field exists (Reynolds & Gilmore 1993) Radial field caused by external field directed towards observer (Whiteoak & Gardner, 1968) Rayleigh-Taylor instabilities between shock and ejecta, streching of magnetic field

15. Magnetic Field Direction in SNRs (Whiteoak & Gardner 1968)

16. Young Shells Predominantly radial field Small scale variations (sub-pc scales) Polarized fraction (PI/TP) 4 to 15% with local enhancements. A large fraction of random magnetic field exists (Reynolds & Gilmore 1993) Radial field caused by external field directed towards observer (Whiteoak & Gardner, 1968) Rayleigh-Taylor instabilities between shock and ejecta, streching of magnetic field

17. Evolved Shells CTB1 10.55 GHz TP+B-Field 100-m-RT

18. The Orientation of bilateral SNRs and the Galactic Magnetic Field G127.1+0.5 HC30 G93.3+6.9

19. Magnetic Field Direction in SNRs (Whiteoak & Gardner 1968)

20. Magnetic Field Direction in G179.0+2.5 = 6cm TP + E-Vectors Old SNR with radial B-Field!!

21. Filled-center SNRs (Tau A) VLA 21cm/6cm, (Bietenholz & Kronberg 1990) 100-m-RT 32GHz, (Reich 2002)

22. G21.5-0.9 Nobeyama Array 22.3 GHz 100-m-RT 32 GHz, (Reich et al. 1998)

23. Depolarization Polarization degree: P(%) = 3  +3  sin   B 0 2 / (B 0 2 + B r 2 ), (Burn 1966) 3  +3   =2  r  2.83  r R=1 rr   8.1 10 5 n B ║   r  (rad) n(cm -3 ) B(Gs)  r(pc) Variation of total power   r Variation of pol. Int.   Sedov equations + strong shock  n 0, B 0, E 0, t age, V shock r I

24. Magnetic Field Strength Assumption: Minimum total energy of electrons, protons and magnetic field. For  =-2 (flux density spectral index = -0.5), and heavy particle energy 100 times electron energy, lower frequency cut 10 7 Hz, upper cut 10 11 Hz:  = relative radiating volume R = radius (arcmin) d = distance (kpc) S 1GHz = flux density (Jy) B = magnetic induction (µGs) Tycho ~ 0.2 mG G127.1+0.5 ~ 12  G B min = 199   -2/7  R -6/7  d -2/7  S 1GHz 2/7 (Pacholczyk 1970) R H Tycho  0.1

25. Magnetic Field Strength: the OH Line at 1720 MHz OH first detected (Weinreb et al. 1963) Maser theory (Litvak et al. 1966) Collision pumping (Elizur 1976) OH about 100 AU behind shock front (Hollenbach & McKee 1989), (Neufeld & Dalgarno 1989) Zeeman splitting 1.31 kHz/mG (Heiles et al. 1993), (Frail et al. 1994, W28)

26. W44 (Claussen et al. 1997) 0.28±0.09mG

27. W51C (Brogan et al. 2000) 1.5±0.05mG 1.9±0.10mG

28. OH 1720 Zeeman Data 10 sources observed Magnetic fields between 0.1 and a few mG W44: W51C Magnetic pressure  10 -7 dyne cm -2 Dynamic pressure: 1/2  0 V s 2  2 10 -7 dyne cm -2 Magnetic pressure: B 2 /8   3 10 -9 dyne cm -2 Thermal pressure: nkT  6-8 10 -9 dyne cm -2

29. Conclusions What can we learn from magnetic field observation? Interaction of SNRs with the Galactic magnetic field SNR parameters In general, the dynamics of SNRs is not affected by the magnetic field In SNRs postshock regions with strong cooling the magnetic field may have increased influence on the dynamics.

30. Thank You On Xinwei day the new star faded away (China, 14 th century B.C.)