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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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slide1

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

Kirit Karkare

Caltech Radio Astronomy Laboratory

CASPER Workshop – August 17, 2010

slide2

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
slide3

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
slide5

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
slide6

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
slide7

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
slide9

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
current system
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
new receiver plans1
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
new receiver plans2
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
flexibility
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
status
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
slide20

Acknowledgements

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