Full Stokes Polarimetry with the Effelsberg Radiotelescope Elena Cenacchi MPIfR Bonn. Alexander Kraus, MPIfR Bonn Karl-Heinz Mack, IRA-INAF Bologna

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1 Full Stokes Polarimetry with the ffelsberg adiotelescope lena Cenacchi MPf Bonn Alexander Kraus, MPf Bonn Karl-Hez Mack, A-NAF Bologna

2 Outle Measurg Circular Polarization Full Stokes polarimetry with a sgle-dish radiotelescope A new calibration procedure for the 00-m ffelsberg telescope Observed Sample The selected sample of extragalactic radio sources Monitorg of the sample at 5 GHz durg 007 xtension of the calibration procedure the range GHz Source Model: Mode Conversion Mode conversion as orig of circular polarization (CP) A theoretical model that can frame the observed data both lear (P) and circular polarization New Polarimetric Survey August, 008: 5 GHz full Stokes survey of the Northern Kühr Catalogue Combed efforts of the ffelsberg and Westerbork adiotelescopes

3 CP and P with a sgle-dish radio-telescope Measurg CP Observed Sample Observed Sample Observed Sample Source Model : Mode Conversion Source Model : Mode Conversion Source Model : Mode Conversion Full Stokes K Full Stokes K Full Stokes Küühr Survey hr Survey hr Survey Jones formalism: used to describe the strument adopted to measure the comg radiation Stokes parameters: used to describe the radio-astronomical source polarimetric properties A perfect strument that doesn t affect the measurements would supply a simple relation of proportionality between the comg radiation and the correspondg measured voltage ( ) i U Q Total Power etectors Multiplyg Polarimeter ( ) ( ) ( ) ( ) i i

4 eceiver fluence on the measurements [ ] [ ] G g G g [ ] [ ] G G G G Measurg CP Observed Sample Observed Sample Observed Sample Source Model : Mode Conversion Source Model : Mode Conversion Source Model : Mode Conversion Full Stokes K Full Stokes K Full Stokes Küühr Survey hr Survey hr Survey

5 Calibration of the 00-m telescope U Müller matrix of the strument Q m m m m 4 3 m m m m 4 Q 3 Q Q Q m 3 m m m U U U U m 4 m m m Mathematical defition of each element up to the nd order (frequency dependent), e.g. m 4 : cos ( ϕ c ) cos ( ϕ c ) cos ( ϕ ) cos ( ϕ ) 4 cos ( ϕ c c )cos ( ϕ ) Cenacchi,. et al., 009, A&A Accep. c c xample at 5 GHz M egular test observations at 5 GHz from ec. 006 to ec ± 0.04% 0.6 ± 0.08% φ -.4 ± 3.8 φ -3.7 ± 8.4 Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

6 Selected sample of extra-galactic radio sources 43 sources: 39 extragalactic sources, planetary nebulae, planets (calibration purpose). Nearly monthly observations at 5 GHz from ecember 006 to ecember 007. CP > 3σ, P 3% CP > 3σ, P < 3% ariable CP Never >3σ Typical CP accuracy of % Good agreement with the few previously known CP values [%], e.g. : Source Michigan 6m BA ffelsberg 3 ffelsberg ± ± ± 0.0, rms ± ± ± ± 0.0, rms 0.5 3C ± ± ± 0.0, rms 0.3 Aller, H.., Aller, M.F., & Plotk,.M From November 007 sgle observg session Homan,.C., Attridge, J.M., & Wardle, J.F.C From the whole set of available measurements Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

7 Multi-frequency polarimetric study Contemporary measurement of,q,u, Frequency dependent Advantages of the new calibration procedure Technical description of the receiver (-terms amplitude and phase) The calibration procedure is suitable to any receiver that supplies circularly polarized puts and is equipped with total power detectors and a multiplyg polarimeter (nowadays the most common receivg architecture) ec. 007 First cross-check: 3 sources observed by ATCA durg a technical session encouragg results, but not enough we start planng a larger survey. CP > 3σ, P 3% Multifrequency study Group Mode conversion candidates Possible correlation among,q,u, variabilities ariable CP CP > 3σ, P < 3% Never >3σ Multifrequency study Group Possible new 0 calibrators Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

8 Multi-frequency polarimetric study The sub-sample of 6 sources that exhibited a CP value systematically above 3σ and an P level greater than 3% has been selected for the first multi-frequency full Stokes study at.7, 5, 8.5 and 0 GHz. Old data for,q,u were available the ffelsberg archive also at.4 and 3 GHz Quasar, z Quasar, z log [Jy] a P % CP P log [GHz] log [GHz] 0767 BAC, z 0.3 (?) 0767 BAC, z 0.3 (?) log [Jy] a P % CP P log [GHz] log [GHz} Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

9 Mode conversion as orig of CP Magnetized plasma of low-energy electrons sotropic particle distribution Non-null component of B perpendicular to the le of sight (e.g. helical field) ariation of the Stokes parameters along the le of sight, accordg to the radiative transfer (emissivity and absorption coefficients) a typical frame appropriately rotated: d η k kqq k ds dq ηq k Q kq k FU ds du k U k FQ kc ds d η k k kcu ds k,q, k F k C Absorption coefficients otation coefficient Conversion coefficient Beckert, T., Falcke H., 00 Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

10 Theoretical model vs. Measured values xtended Unpolarized Synchrotron Source 8x0 cm n e 0-3 cm -3 p.45 B 4 mg quipartition Compact Jet Component.5x0 9 cm n e 5x0 - cm -3 B 90 mg Helical B χ 85 δ 6 3 rd Component? Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Küühr Survey

11 The 5 GHz Northern Kühr full Stokes survey Westerbork Array ffelsberg Telescope 4 x 5-m dishes terferometer.7 km lear array quatorial mountg Native lear feeds at 5 GHz Sgle dish radiotelescope 00-m diameter antenna Alt-Azimutal mountg Native circular feeds at 5 GHz i s ( ) x x y y y x COATO POST POCSSNG Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Kühr Survey

12 The 5 GHz Northern Kühr full Stokes survey Aug. 8th-th, 008: B-WB contemporary observation Northern Kühr Cataloge 83 pot like sources at δ > -0, flux > Jy at 5 GHz 44 Sources (cludg calibrators) observed by both the struments CP CABATON 75 Sources observed by ffelsberg only, -0 < δ Sources observed by Westerbork only, δ >30 UPAT FU STOKS CATAOGU ffelsberg data already reduced, Westerbork reduction currently ongog at A Measurg CP Observed Sample Source Model : Mode Conversion Full Stokes Kühr Survey

13 Conclusions So far A new polarimetric calibration for the ffelsberg telescope has been developed, allowg full Stokes measurements with an overall accuracy CP of % Nearly monthly observations of a sample of 39 extragalactic radio sources have been carried at 5 GHz, durg 007. Nearly 30% of the CP detections are over 3σ Sources that systematically exhibited CP above 3σ and P>3% were object of a first full Stokes multi-frequency study, durg 008, to vestigate the mode conversion process Comparison with a theoretical model, to derive the physical properties of the source magnetic field and surroundg medium. 5 GHz Northern Kühr full Stokes survey, August 8th-th 008, performed by ffelsberg and Westerbork together. and the next future Completion of the data reduction from the polarimetric survey (Westerbork part) xtension of the multi-frequency full Stokes observations to other sources, selected from the Kühr polarimetric survey nd of Ph planned by the end of 009