Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Tied Array Beams with TBBs

transientskp
December 03, 2012

Tied Array Beams with TBBs

J. Emilio Enriquez

transientskp

December 03, 2012
Tweet

More Decks by transientskp

Other Decks in Science

Transcript

  1. Tied Array Beams with TBBs
    Heino Falcke, Sander ter Veen, Arthur Corstanje, Pim Schellart.
    J. Emilio Enriquez
    LOFAR TKP Meeting Dec 3 2012

    View Slide

  2. FRATS : Fast Radio Transients
    ž  Millisecond pulses originating from:
    —  Pulsars
    —  Flaring stars
    —  Lightning from Saturn
    —  Jupiter aurora radio emission
    —  Exoplanets?
    —  SETI ??

    View Slide

  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

    View Slide

  4. One second of data...
    PSR B0329+54

    View Slide

  5. De-dispersed Dynamic Spectrum
    PSR B0329+54

    View Slide

  6. LOFAR Station: CS002
    Sanity check of coherent
    addition

    View Slide

  7. Station beam addition
    SNR ~ 9 SNR ~ 25
    (~√6 better, as expected for
    incoherent addition)

    View Slide

  8. Self Calibration:
    ž  Calibration of
    stations by Cross
    Correlation on the
    brightest pulse.
    ž  Most delay values
    are in the sub-
    sample time scale.

    View Slide

  9. PSR B0329+54
    In-coherent

    View Slide

  10. Coherent
    PSR B0329+54

    View Slide

  11. PSR B0329+54
    4
    5
    1
    2
    3
    6
    7

    View Slide

  12. Current Work :
    Station beam addition
    SNR ~ 25 SNR ~ 50 (expect ~60)

    View Slide

  13. PSR B0329+54
    pol 0 pol 1 pol 0+1
    pol 0 pol 1 pol 0+1

    View Slide

  14. Single Station Imaging
    Jana Koehler
    Arthur Corstanje

    View Slide

  15. Multi-Station Imaging
    156.2 MHz
    Time axis
    At pulse time
    Frequency axis
    PSR B0329+54

    View Slide

  16. 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

    View Slide



  17. View Slide

  18. 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?

    View Slide

  19. PSR B0329+54
    ž  Pulsar (also PSR J0332+5434).
    ž  Distance: 809.79 pc
    ž  Period: 0.71452 sec
    ž  Exoplanets?
    PSR B0329+54

    View Slide

  20. 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
    > just by
    calculating the RM
    and DM.

    View Slide

  21. 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.

    View Slide

  22. ž  DM = 27.1 pc/cm3 … (26.83 from literature) PSR B0329+54

    View Slide

  23. ž  Dv = 2/3 MHz
    ž  RM ~ 65.8 rad/m2
    (where literature
    shows RM~63.7)

    View Slide

  24. 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  > ~ 30
    ž  Scattering ?

    View Slide

  25. De-dispersed Dynamic Spectrum
    1
    2
    3
    PSR B0329+54

    View Slide

  26. View Slide

  27. 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

    View Slide

  28. 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
    =

    View Slide

  29. 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)

    View Slide

  30. 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.

    View Slide

  31. 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

    View Slide