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Dependence of the Integrated Faraday Rotations on Total Flux Density in Radio Sources

Dependence of the Integrated Faraday Rotations on Total Flux Density in Radio Sources. Chen Y.J, Shen Z.-Q. Background of Integrated RM in BL Lac. Dependence of EVPA on wavelength squared For BL Lacs, Our galaxy makes the most contribution to the observed RM between 1.4 to 1.6 GHz.

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Dependence of the Integrated Faraday Rotations on Total Flux Density in Radio Sources

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  1. Dependence of the Integrated Faraday Rotations on Total Flux Density in Radio Sources Chen Y.J, Shen Z.-Q

  2. Background of Integrated RM in BL Lac • Dependence of EVPA on wavelength squared • For BL Lacs, Our galaxy makes the most contribution to the observed RM between 1.4 to 1.6 GHz

  3. Background Analysis • Polarized VLBI observations show that the maximum RM is frequently much more than 100 rad/ m2, up to several thousand is not unusual in some quasars; Galactic contributions is not enough • BL Lac objects show little or no emissions lines. It means the surrounding medium is very tenuous • Synchrotron emission comes from charges moving in magnetic field; The source itself must have contribution to the observed RM • Wide band of EVPA with squared lamda reflects to some degree the true RM estimation

  4. Process in searching for sample • There should be long term monitoring measurements of multi-frequency polarimetric observations available. • Michigan University DATA base: 5, 8, 15GHz, no longer available • VLBA polarization calibrators: 137 sources; 27 of them over 10 epochs

  5. Measurements with VLA • Observational Frequencies: 5 GHz, 8 GHz, 22 GHz and 43 GHz • Uniformly distributed in right ascension • Observed monthly for those famous sources • Calibrators: 3C48 (0137+331) and 3C286 (1331+305)

  6. Measurements with VLA • Configure: A B C D; The same configure used in one epoch • Measurement: R/L Phase Difference, twice the EVPA • All EVPA values are normalized to the range of -/2 to /2 →n ambiguities

  7. Uncertain factors in RM Estimation and Alleviation • Uncertain Factors: • n ambiguities • Antenna beam smoothing: in a beam size including components of different spectral index: f=pcos, → • Beam size varies with frequency, hence including different components at different freq. →different  • Using the configure at different frequencies at one epoch • Observed at 4 frequencies alleviate the n ambiguity effect to some degree • Long-term monitoring will increase credibility of RM and flux correlation results

  8. RM FITTING SITUATION (example: 0238+166)

  9. Statistic Distribution of RM • 25 OF 27 sources have maximum absolute RM values larger than 200 • n ambiguities will most probably underestimate these values

  10. Variation of RM with Flux density

  11. Variation of RM with Fractional Polarization

  12. Correlation Results of RM with flux density and Fractional Polarization

  13. Statistical Results • Quasar: 19; BL Lac: 4(RBL); Galaxy: 3; U: 1 • 14 of 27 sources show strong correlation of RM with total flux density • 9 of 27 sources show correlation of RM with fractional polarization • 6 of 27 sources show correlation of RM with both total flux density and fractional polarization

  14. DISCUSSION • The resultant RM at 4 frequencies from 1.45 to 1.65 GHz can be used to correct PA at higher frequencies to some degree (e.g. 4.8 GHz, 15GHz) (Rudnick et al. AJ 88,518) • The intrinsic EVPA is similar over wide separations in wavelength • CP is Faraday converted from LP (Faraday Conversion) within jet. • RM may dominantly occurs within jet, and related to total flux density

  15. Summary • RM is variable with time in the selected sample • About half of the 27 source show correlation with flux density, about 9 of them have correlation with fractional polarization, in spite that n ambiguities may weaken the correlation relationship • RM in the selected sample may predominantly arise from targets itself, not from medium outside • RM is correlated with flux density, suggesting that in emission particle number density might be related to flux density assuming magnetic field keeps constant

  16. KVN USAGE IN POLARIZATION AGN RESEARCH BLAZARS have higher fractional polarization at higher frequency Polarization Structure at very high frequency closer to acceleration and collimation region RM distribution reveal more information around emission region

  17. Thank Your For Your Attention

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