Tied Array Beams with TBBs

J. Emilio Enriquez

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
   

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

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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
   

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

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5. De-dispersed Dynamic Spectrum
   PSR B0329+54
   

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6. LOFAR Station: CS002
   Sanity check of coherent
   addition
   

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

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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.
   

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9. PSR B0329+54
   In-coherent
   

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10. Coherent
    PSR B0329+54
    

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

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

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

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14. Single Station Imaging
    Jana Koehler
    Arthur Corstanje
    

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

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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
    

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17. 
    
    

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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?
    

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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
    

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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.
    

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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.
    

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

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

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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 ?
    

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

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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
    

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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
    =
    

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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)
    

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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.
    

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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
    

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