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

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

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 

One second of data... PSR B0329+54 

De-dispersed Dynamic Spectrum PSR B0329+54 

LOFAR Station: CS002 Sanity check of coherent addition 

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

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

PSR B0329+54 In-coherent 

Coherent PSR B0329+54 

PSR B0329+54 4 5 1 2 3 6 7 

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

PSR B0329+54 pol 0 pol 1 pol 0+1 pol 0 pol 1 pol 0+1 

Single Station Imaging Jana Koehler Arthur Corstanje 

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

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 


 

  

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? 

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

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. 

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. 

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

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

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 ? 

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

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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 

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 = 

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) 

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. 

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