43 and 86 GHz VLBI Polarimetry of 3C Adrienne Hunacek, MIT Mentor Jody Attridge MIT Haystack Observatory August 12 th, 2004

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1 43 and 86 GHz VLBI Polarimetry of 3C454.3 Adrienne Hunacek, MIT Mentor Jody Attridge MIT Haystack Observatory August 12 th, 2004

2 Introduction Quasars subclass subclass of Active Galactic Nuclei (AGN) Extremely large redshifts mean they are tens of billions of light years away This implies they are extremely luminous 3C has redshift z=0.859, optical magnitude 16.1 False color X-ray image: A. Siemiginowska Illustration: M. Weiss

3 These objects are also extremely compact (only tens of light years across) The model for these bright, compact sources is a central supermassive black hole (10 7 to 10 9 solar masses) Material from passing stars forms accretion disk that radiates as it is consumed by black hole Emits ionized gas which form two jets moving away from black hole, perpendicular to accretion disk

4 Synchrotron radiation, relativistic beaming One jet is pointing almost directly at us, other is pointing away and can t be observed Faraday rotation: polarization in the jet may be rotated before it reaches us To minimize effects, go to higher frequencies (RM λ 2 ) Polarization gives us information about the structure of quasar Magnetic field structures trace plasma in jet

5 Angular resolution is proportional to wavelength divided by telescope aperture In typical radio wavelength (7 mm) you would need a telescope several kilometers across to get one arcsec of resolution VLBI solves this problem by observing one source with two or more telescopes that are far apart from each The array of telescopes effectively serves as a large telescope aperture and gives increased resolution The VLBA antenna at Owens Valley, CA Image courtesy of NRAO

6 Data were taken using Very Long Baseline Array (VLBA), an array of 10 telescopes used for VLBI For typical 7 mm wavelengths, VLBA gives angular resolution of milliarcseconds Individual telescopes are synchronized by atomic clocks Data is recorded onto magnetic tapes and correlated on a computer

7 Imaged before at 43 GHz (and lower) General structure of 3C454.3 is core on eastern end and ejected superluminal components in form of radio jet to west Quasi-stationary stationary shock model In highly polarized quasars (HPQs( HPQs), polarization parallel to jet direction Previous Results

8 43 GHz image of 3C454.3 Marscher (1998) He measured speed of superluminal component to be 13 c (12/94-10/95)

9 43 GHz image by Gomez et al. (1999) They also identified a bright stationary component (St) about 0.6 mas from core Also saw bright moving component A at 0.26 mas Measured speed at 2.9 c Difference from Marscher---different velocities?

10 Observations and Calibration Data reduced using NRAO Astronomical Image Processing System (AIPS) Caltech software package Difmap,, to self- calibrate and CLEAN Took data back to AIPS, corrected for D-D terms, made polarization image Difficulties with 86 GHz calibration

11 43 GHz images of 3C454.3 Discussion of Images

12 We did see a component 0.24 mas from core Is this the component A identified by Gomez et al? Stationary shock wave model Large N/S spread suggests wide opening angle Why does jet later collimate? Something restricts expansion? Is there something that causes it to bend? Evidence for a helical jet? Many unanswered questions

13 86 GHz images of 3C454.3

14 Modelfit data for 3C454.3, 43 GHz (top) and 86 Ghz (bottom)

15 D Q8 Q7 Q6 W4 W3 W1 W2

16 For W4=Q8, χ=11.6 between 43 and 86 GHz images implying a RM of ~ 5500 rad/m 2 For W3=Q7, χ=8.3 between 43 and 86 GHz images implying a RM of ~ 4000 rad/m 2 For W2=Q6, χ=5.0 between 43 and 86 GHz images implying a RM of ~ 2400 rad/m 2 Rotation measure decreasing down jet, agrees with theory (Taylor 1998) Indicates presence of Faraday screen between us and the source

17 Conclusions and Future Work 86 GHz can be done for something other than 3C279 and 3C273 Future epochs to look for movement and/or stationary shocks More observations at 86 GHz for comparison Better observations, all 9 antennas of VLBA, European antennas to give us higher resolution Some way of calibrating EVPAs at 86 GHz? Try and fit helical jet models to data Some way of getting absolute amplitude calibration in order to look at spectral indices

18 Acknowledgments Thanks to Joe Salah and the Haystack Observatory Staff for a great summer Fellow REU students for fun times outside of work The NSF for funding this REU Most of all to Jody for being a terrific mentor and teaching me so much!