1. First Result of Urumqi 6cm Polarization Observations: Xiaohui Sun, Wolfgang Reich JinLin Han, Patricia Reich, Richard Wielebinski Partner Group of MPIfR at NAOC New 6cm Maps of Cygnus Loop

2. Outline Introduction to the Cygnus Loop Previous results at radio band New 6cm observations and results –System and observational parameters –New 6cm map of the Cygnus Loop –Spectral index map –Rotation Measure results –Depolarization analysis Conclusions

3. Introduction to the Cygnus Loop Location: –little obscuration from the Galactic plane Size: ~ –ideal for Urumqi 25m dish at 6cm Distance: 540 pc (HST observation) –Very precise –nearby and hence little confusion by local medium Age:~14,000 yr –just transition from adiabatic to radiative phase Appearance: (Cavity explosion, interaction with cloud?) –bright NE and WEST shells at radio, optical and X-ray –bright south shell at radio

4. Previous Results at Radio Band Spectral index – need high frequency total intensity dataSpectral index –integrated flux density 11cm, 20cm and 35cm data   =-0.42  0.06 (Uyaniker et al. 2004) 6cm flux density: 73Jy  spectral steepening (Kundu & Becker 1972) –spatial variation over the SNR and spectral curvature 408MHz, 1420MHz and 2695MHz data  large spectral variation (Green 1990; Leahy & Roger 1998) NOT supported by high quality data (Uyaniker et al. 2004) Polarization – need high frequency polarization data –rotation measure south part: -20 rad/m 2 (Uyaniker et al. 2002; Kundu & Becker 1972) –depolarization at the northern part NE region, internal depolarization (Leahy et al. 1997) –Appearance substantial difference between the south and the north part  two-SNR scenario (Uyaniker et al. 2002)

5. Spectral index of flux density: -flux density -frequency Spectral index of brightness temperature:

6. Previous Results at Radio Band Spectral index – need high frequency total intensity data –integrated flux density 11cm, 20cm and 35cm data   =-0.42  0.06 (Uyaniker et al. 2004) 6cm flux density: 73Jy  spectral steepening (Kundu & Becker 1972) –spatial variation over the SNR and spectral curvature 408MHz, 1420MHz and 2695MHz data  large spectral variation (Green 1990; Leahy & Roger 1998) NOT supported by high quality data (Uyaniker et al. 2004) Polarization – need high frequency polarization data –rotation measure south part: -20 rad/m 2 (Uyaniker et al. 2002; Kundu & Becker 1972) –depolarization at the northern part NE region, internal depolarization (Leahy et al. 1997) –Appearance substantial difference between the south and the north part  two-SNR scenario (Uyaniker et al. 2002)

7. System and Observational parameters Frequency: 4.8 GHz Bandwidth: 600 MHz Tsys: 22 K-25 K HPBW: 9.5 arcmin First Sidelobe: 2% Instrumental polarization: peak 0.5% ring: 2% Tracking error: <1 Map Center: (20 h 52 m, 30  30) Map Size: 4.2  4.8  Scan velcity: 2  /min Scan separation: 4 Integration time: 2 min/pixel Scan direction: RA and DEC Observation Date: 8/2004-12/2004 Coverages I (PI): 5 (6) SourceFlux density (Jy) PC (%) PA (  ) 3C2867.511.333 3C48 5.51  0.104.2  0.4108.1  1.5 3C138 3.97  0.0710.8  0.5168.8  1.2

8. Reduction spike and interference scanning effects calibration combine data HPBW (CL2): 9.7 arcmin r.m.s-I: 1 mK T B (0.6) r.m.s-PI: 0.4 mK T B (0.35) CL4 CL2 New 6cm Map

9. CL4 (2048+312): Variable extragalactic origin, z=3.18 angular broadening time scale: 48 days variation: 30%

10. NE1 15% NE2 20% C 25% W 20% S3 20% S2 25% S1 20% New 6cm Map

11. Effelsberg 11cm and 21cm Map

13. Spectral index: integrated flux density Integrated flux density: 90  9 Jy 20% larger than previous value (miss diffuse component) Consistent with Uyaniker et al (2004) No spectral steepening or flattening until 5 GHz New measurement

14. Spectral index Map: 6cm/11cm/21cm zerolevel (TT-plot) 6cm +2 mK 11cm +8 mK 21cm +23 mK limit: ~20  r.m.s high signal-to-noise ratio influence of background spectral index variation NE, SW, NW, CL4: -0.4 Increase towards diffuse region, maximal difference ~0.3, support Uyaniker et al. (2004) Qualitatively explanation In diffuse region: magnetic field less compressed, high energy electrons contribute

15.  6cm/11cm -  6cm/21cm spectral curvature >0: flattening <0: steepening Difference map: | |<0.15 south, NW, NE: >0 Middle: <0 NO spectrum curvature support Uyaniker et al. (2004)

16. Rotation Measure results: South Calculation: linear fitting the PAs at 6cm, 11cm and 21cm (PI > 5  r.m.s) Results: South partSouth part –-21 rad/m 2 –Rotation of PA ~4  intrinsic magnetic direction magnetic field along the shell –Consistent with previous results –Foreground contribution n e =0.02 cm -3, B || =-3  G, D=540 pc  RM=-26 rad/m 2

18. Rotation Measure results: South Calculation: linear fitting the PAs at 6cm, 11cm and 21cm (PI > 5  r.m.s) Results: Southern part –-21 rad/m 2 –Rotation of PA ~4  intrinsic magnetic direction magnetic field along the shell –Consistent with previous results –Foreground contribution n e =0.02 cm -3, B || =-3  G, D=540 pc  RM=-26 rad/m 2

20. Rotation Measure results: North Region C:Region C –RM=-28 rad/m 2 –Projection? Region NE1, NE2 and W: –21cm totally depolarized –Ambiguity n  362 rad/m 2 –Average RM for three possibilities: N=0: RM=-73 rad/m 2 N=-1: RM= 290 rad/m 2 N=1: RM= -430 rad/m 2

22. Rotation Measure results: North Region C: –RM=-28 rad/m 2 –Projection? Region NE1, NE2 and W:NE1, NE2 and W –21cm totally depolarized –Ambiguity n  362 rad/m 2 –Average RM for three possibilities: N=0: RM=-73 rad/m 2 N=-1: RM= 290 rad/m 2 N=1: RM= -430 rad/m 2

24. Rotation Measure results: North Region C: –RM=-28 rad/m 2 –Projection? Region NE1, NE2 and W: –21cm totally depolarized –Ambiguity n  362 rad/m 2 –Average RM for three possibilities: N=0: RM=-73 rad/m 2 N=-1: RM= 290 rad/m 2 N=1: RM= -430 rad/m 2

25. Minimum Rotation Measure Case (n=0)

26. Large Rotation Measure Case (n=1):NE1+NE2 Magnetic field: energy equipartition  47  G –Flux density: 11 Jy –Spectral index: -0.4 –Emission volume: 400 pc 3 Electron density: 1 cm -3  pressure balance –10-100 cm -3  Optical filament observation O VI (Long et al. 1992) S II (Patnaude et al. 2002) –Several cm -3  X-ray observation ASCA (Miyata et al. 1994) ROSAT (Lu & Aschenbach 2005) Depth of the filament: 4.8 pc  RM=-128 rad/m 2 strict lower limit by a factor of a few

27. Large Rotation Measure Case (n=1)

28. Depolarization Analysis Description of depolarization: Depolarization mechanism: –Bandwidth depolarization: –Internal depolarization: –External depolarization: –Beam depolarization Similar to external depolarization Depends on the resolution Polarization angle changes in the scale of beam size

29. Depolarization Analysis Bandwidth depolarization NOT important –  =600 MHz @ 6cm –  =40 MHz @ 11cm –  =20 MHz @ 21cm Beam depolarization is NOT important –No distortions in polarization angle maps –Depolarization does not depend on the resolution (both at 10 arcmin and 1 arcmin)

30. Depolarization Analysis Southern part and C filament –Observation: PC 6cm ~PC 11cm ~PC 21cm –Explanation: no depolarization Northern part –Observation: DP 21cm ~0 NE1: PC 6cm ~27% PC 11cm ~23% NE2: PC 6cm ~28% PC 11cm ~23% W: PC 6cm ~20% PC 11cm ~15% –Minimal RM case (-73 rad/m 2 ): DP 6cm =94% DP 11cm =50% –Large RM case (-430 rad/m 2 ): DP 6cm ~0 –Large RM case (290 rad/m 2 ): DP 6cm =33% DP 11cm =12%

31. Remarks on Two-SNR picture Different properties between the northern part and the southern part at: radio (new observations) other bands (X-ray, optical, …) Interaction of the two SNR: Similar distance no enhancement in the overlap (SNRs DEM L316 in LMC Williams et al. 1997)

32. Conclusions No spectral curvatures in: –Spectrum of integrated flux density –Overall spectral maps RM –-21 rad/m 2 for southern part  foreground –-73 rad/m 2 or 290 rad/m 2 for the northern part –Internal depolarization at the northern part Two-SNR scenario –Different properties in the south and north