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Tied Array Beams with TBBs

December 03, 2012

Tied Array Beams with TBBs

J. Emilio Enriquez


December 03, 2012

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  1. Tied Array Beams with TBBs Heino Falcke, Sander ter Veen,

    Arthur Corstanje, Pim Schellart. J. Emilio Enriquez LOFAR TKP Meeting Dec 3 2012
  2. FRATS : Fast Radio Transients ž  Millisecond pulses originating from:

    —  Pulsars —  Flaring stars —  Lightning from Saturn —  Jupiter aurora radio emission —  Exoplanets? —  SETI ??
  3. How to detect them? LOFAR hardware/software FRATS Tools ž  All

    Sky —  LOFAR ž  All the time —  Parallel Observations (Piggybacking). —  Triggering ◦  Sander’s Talk ◦  ARTEMIS ◦  Others… ž  Look back in time —  TBBs (1-5 sec) —  Offline processing. ž  Bright events —  Coherent addition: ◦  High SNR ž  Accurate position —  Multi-station Imaging
  4. Station beam addition SNR ~ 9 SNR ~ 25 (~√6

    better, as expected for incoherent addition)
  5. Self Calibration: ž  Calibration of stations by Cross Correlation on

    the brightest pulse. ž  Most delay values are in the sub- sample time scale.
  6. Summary Future Work ž  Coherent Beams ž  Multi-Station Imaging ž 

    Use larger number of stations ž  FRATS pipeline —  RFI mitigation (from CR tasks) —  Antenna gain ž  Imaging: —  projected station positions —  Store complex beams from beamformed LOFAR data
  7. Outline ž  Method —  Dedispersion? —  Incoherent Station Addition — 

    Self Calibration —  Coherent Station Addition —  Imaging (preliminary) ◦  Jupiter all-sky Image ◦  Pulsar Image ž  Example —  Linear polarization (faraday rotation) —  Period? DM?
  8. PSR B0329+54 ž  Pulsar (also PSR J0332+5434). ž  Distance: 809.79

    pc ž  Period: 0.71452 sec ž  Exoplanets? PSR B0329+54
  9. Some more fun physics… ž  DM by measuring the time

    delay. ž  RM by measuring the bandwidth needed for full polarization shift. ž  We can calculate <B|| > just by calculating the RM and DM.
  10. How to detect them? ž  All Sky —  LOFAR Beamsize:

    LBA: All-sky (30000 sq. deg) HBA: 500 sq. deg ž  All the time —  Parallel observations —  Internal and external triggers. (AARTFAAC, ARTEMIS, Nancay trigger?, Xray telescopes?) ž  Look back in time.
  11. ž  Dv = 2/3 MHz ž  RM ~ 65.8 rad/m2

    (where literature shows RM~63.7)
  12. PSR B0329+54 ž  Distance: 809.79 pc ž  Period : 0.71452

    sec ž  DM = 27.1 pc/cm3 ž  Polarization ž  RM = 65.8 rad/m2 ž  <B|| > ~ 30 ž  Scattering ?
  13. ž  import numpy as np ž  RM=63.7 ž  v1=130e6 ž 

    v2=145e6 ž  c=3e8 ž  l1=c/v1 ž  l2=c/v2 ž  v3=130.667e6 ž  l3=c/v3 ž  RM*(l1**2-l3**2)*57 ž  v4=145.667e6 ž  l4=c/v4 ž  RM*(l2**2-l4**2)*57 ž  (Out[22]+Out[25])/2 ž  180/(RM*57) = 0.049574485664711225 ž  v5=160e6 ž  l5=c/v5 ž  np.sqrt(l5**2+0.049574485664711225)=1.888173 ž  c/1.888173/1e6 = 158.88369715755792 ž  158.88369715755792 -160 = -1.1163 MHz band
  14. The Stationary, Quasi-Monochromatic Radio-Frequency Interferometer X s s b c

    g / s b⋅ = τ ) ( cos 2 t E V ω = ] ) ( cos[ 1 g t E V τ ω − = ] ) 2 ( cos ) ( [cos g g t P ωτ ω ωτ − + multiply average The path lengths from sensors to multiplier are assumed equal! Geometric Time Delay Rapidly varying, with zero mean Unchanging ) ( cos g C P R ωτ =
  15. LOFAR and TBBs ž  Transient Buffer Board (TBBs): —  RAM,

    used as ring buffer, on each LBA/HBA ž  Data Storage: ring stopped, dump to disk. ž  Can reproduce any LOFAR signal. ž  1Gb memory ~ 1 sec /antenna element —  (5 sec in the future)
  16. Dispersion Measure (DM) ž  Dispersive nature of interstellar plasma: radio

    wave interaction with free electrons makes for slower group velocities for lower frequencies. ž  Time delay is calculated by: ž  DM Total column density of free electrons, or a distance estimate with ne models of the ISM.
  17. Faraday Rotation ž  If the ISM has a B, then

    it becomes birefringent. ž  LCP and RCP have different refractive index : different group velocities. ž  Rotates linearly polarized waves. λ Pulsar B A β Aristeidis Noutsos, Astronomische Gesellschaft 2010 PSR B0329+54 d β = λ2 * RM RM = π*/(λ1 –λ2 )2