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KuPol: A New Ku-Band Polarimeter for the OVRO 40-Meter Telescope

KuPol: A New Ku-Band Polarimeter for the OVRO 40-Meter Telescope. Kirit Karkare Caltech Radio Astronomy Laboratory CASPER Workshop – August 17, 2010. In Collaboration With. Tony Readhead Timothy Pearson Kieran Cleary Glenn Jones Oliver King. Rodrigo Reeves Vasiliki Pavlidou

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KuPol: A New Ku-Band Polarimeter for the OVRO 40-Meter Telescope

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  1. KuPol:A New Ku-Band Polarimeter for the OVRO 40-Meter Telescope Kirit Karkare Caltech Radio Astronomy Laboratory CASPER Workshop – August 17, 2010

  2. In Collaboration With • Tony Readhead • Timothy Pearson • Kieran Cleary • Glenn Jones • Oliver King • Rodrigo Reeves • Vasiliki Pavlidou • Martin Shepherd • Walter Max-Moerbeck • Joey Richards • Matthew Stevenson

  3. The OVRO 40-Meter Telescope • Located near Big Pine, CA, 4 hours north of Los Angeles • Built in 1966 • Alt-azimuth, f = 0.4 • Previously used for VLBI with Parkes and CMB experiments

  4. The OVRO 40-Meter Telescope

  5. Current Activity (Healey et al, 2008) • Monitoring 1158 candidate gamma-ray blazars • CGRaBS objects with δ > -20° • In collaboration with Fermi Gamma-ray Space Telescope

  6. Blazars • Active galactic nuclei driven by matter accreting into supermassive black holes at the centers of galaxies • Blazars have jets oriented down line of sight • No accepted model for jet acceleration, emission, composition

  7. Science Goals • Correlate radio and gamma-ray light curves • Choose between different models of jet composition, distance from central engine • Delay between radio and gamma-ray peaks can tell us where they are created in the blazar

  8. First Results – Light Curves

  9. Radio lags Radio precedes First Results Gamma-ray flux density Radio flux density • Radio/gamma-ray time lags need longer duration light curves • Radio/gamma-ray flux density correlation is significant

  10. Current System • Dual-beam Dicke-switch radiometer • Single band from 13-16 GHz, 30 K system temp • Lose a factor of sqrt(2) in sensitivity from ideal receiver • What would we like? • Increased sensitivity • Wider bandwidth • Spectral capabilities (not so important for blazars) • Polarization – variability is related to magnetic field structure in jet emission region

  11. Current System

  12. New Receiver Plans

  13. New Receiver Plans • Analog front end: • Combined correlation polarimeter and balanced dual-beam radiometer • Intensity difference between two beams, polarization through correlation • 12-18 GHz • 12 * 500 MHz bands • 20 K system temperature • RF over Optical link down the feed legs to the back end in the control room

  14. Front End Plans

  15. New Receiver Plans • Digital back end: • One ROACH, two iADCs for each of the twelve 500 MHz bands • ROACH at 250 MHz, iADCs at 1 GHz • MHz spectral resolution • Identical programming for each ROACH • Inputs: (A_LCP – B_LCP), (A_LCP + B_LCP), (A_RCP – B_RCP), (A_RCP + B_RCP) • FFT, Demodulate → A_LCP, A_RCP, B_LCP, B_RCP • Stokes → For each horn we get LCP_pow, RCP_pow, real and imaginary components of Q and U

  16. Flexibility • Each of the 12 * 500 MHz bands is independent – can add identical modules to increase bandwidth • Different instruments on same receiver • High resolution spectrometer • RFI excision

  17. Status • Horn design complete • Entire front-end RF chain purchased or being fabricated • OMTs, waveguide phase shifters in fab queue at NRAO • ROACH design almost complete • Commissioning in early 2011

  18. Acknowledgements • CASPER Group • CfA travel funding • Caltech Summer Undergraduate Research Fellowship (SURF program) • Rose Hills Foundation SURF Fellowship

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