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
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. One second of data... PSR B0329+54
5. De-dispersed Dynamic Spectrum PSR B0329+54
6. LOFAR Station: CS002 Sanity check of coherent addition
7. Station beam addition SNR ~ 9 SNR ~ 25 (~√6 better, as expected for incoherent addition)
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.
9. PSR B0329+54 In-coherent
10. Coherent PSR B0329+54
11. PSR B0329+54 4 5 1 2 3 6 7
12. Current Work : Station beam addition SNR ~ 25 SNR ~ 50 (expect ~60)
13. PSR B0329+54 pol 0 pol 1 pol 0+1 pol 0 pol 1 pol 0+1
14. Single Station Imaging Jana Koehler Arthur Corstanje
15. Multi-Station Imaging 156.2 MHz Time axis At pulse time Frequency axis PSR B0329+54
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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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?
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
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 <B|| > just by calculating the RM and DM.
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.
22. ž  DM = 27.1 pc/cm3 … (26.83 from literature) PSR B0329+54
23. ž  Dv = 2/3 MHz ž  RM ~ 65.8 rad/m2 (where literature shows RM~63.7)
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  <B|| > ~ 30 ž  Scattering ?
25. De-dispersed Dynamic Spectrum 1 2 3 PSR B0329+54
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
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 =
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)
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.
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