Recent Developments on FRATS

Transcript

1. Recent developments on FRATS Sander ter Veen Heino Falcke, Emilio

   Enriquez, Anya Bilous, Jörg Rachen, Pim Schellart In collaboration with Cosmic Ray KSP and Pulsar Working Group 1

2. FRATS Real-time detection of Fast Radio Transients 2 •  Science:

   •  Millisecond pulses •  Searching for Unknown Objects •  Searching for Unknown classes/ processes •  Statistics on known sources •  Fishing expedition •  Fast: beamforming mode

3. Objects emitting millisecond pulses 3 Pulsars/ RRATs (exo) planets Humans

   Flare stars

4. Catch them all! Fish in the big pool 4 Incoherent

   summation of the station beam Keeps large FoV Parallel observing to other observations FoV (sq. degr) LBA INNER LBA OUTER 30 MHz 419 65.8 60 MHz 105 16.5 HBA CORE HBA 150 MHz 18.4 10.3

5. Disperion “refractive index of space” 5 •  Dispersion effect: Signal

   at lower frequencies arrive later. •  Data is split in small channels (~ kHz ) •  Channels are summed according to dispersion law •  Many (>100) DM trials Lorimer et al. 2007 Trigger moment Stop delay

6. What is it? 6

7. What is it? Is it celestial? 7 Lorimer Burst Lorimer

   et al. 2007 Is it a Peryton? Burke-Spoloar et al. 2010 Need an array for confirmation! Two more found!

8. Trigger on source Real-time detection. 8 Dedispersion in multiple frequency

   bands Coincidence requirement between the bands

9. Transient Buffer Board (TBBs) RAM Ring buffer for each LBA/HBA

   element Data stored, stopped, dumped to disk. Reproduce any LOFAR signal; Also your data! Limited memory => limited time Beamsize: LBA: All-sky (30000 sq. degr) HBA: 500 sq. degr. 9

10. Use TBB data to identify the source Real-time detection. 10

    Dedispersion in multiple frequency bands Coincidence requirement between the bands Image from TBB data Use to identify source +Multiwavelength Follow-up 4 stations See Presentation by Emilio at 17:05

11. FRATS + MSSS LBA •  MSSS LBA •  All-sky observations

    •  3 beams of 8x2 MHz •  Test observations have run •  100 hours remaining •  1 locus node per beam •  150 DM trials 11

12. Search parameters: Maximum DM •  After trigger, same bandwidth should

    be available in TBB data for easy checking •  Dispersion delay •  ΔtDM =1.3 s (buffer length) •  Max DM depends on frequency 12

13. DM step and time window 13 •  Error in DM

    trial vs DM pulse •  Decreases efficiency •  Compared samples summed for for one DM trial compared to the next •  150-200 DM trials in real-time •  ΔDM=0.1 reasonable •  Lower frequencies problematic, skip? •  Time window 200 ms

14. Coincidence between bands single triggers 14

15. Coincidence between bands dual channel triggers 15

16. Coincidence between bands triple channel triggers 16

17. RFI mitigation: Raw data 17

18. RFI mitigation: Divide by spectrum 18

19. RFI mitigation: Flagging method •  Gaussian data: •  Flag channels

    that are outliers •  Narrow time flagging: -  Dedisperse DM=0 -  Coincidence of 2 bands 19 n ⌅ i=1 a2 i ⇥ n ⌅ i=1 ai ⇤2 = C

20. RFI mitigation: Flag RFI 20

21. Different averages per block 21 Top to bottom: 73-75 MHz

    65-67 MHz 60-62 MHz 54-56 MHz 48-50 MHz 42-44 MHz 36-38 MHz 30-32 MHz Arbitrary offset between channels

22. Artifacts in dedispersed data 22 Top to bottom: 73-75 MHz

    65-67 MHz 60-62 MHz 54-56 MHz 48-50 MHz 42-44 MHz 36-38 MHz 30-32 MHz Arbitrary offset between channels

23. RFI mitigation: Subtract average timeseries (zeroDM-ing) 23

24. Sometimes there is just too much RFI 24

25. Manual trigger verification 25 BAD

26. Manual trigger verification Real pulse from B1919+21 26 Good

27. Trigger settings MSSS LBA 8x 2 MHz bands at: 30-32

    MHz 36-38 MHz 42-44 MHz 48-50 MHz 54-56 MHz 60-62 MHz 65-67 MHz 73-75 MHz DM range 0-15 pc cm-3 DM step: 0.01 pc cm-3 Coincidence time window: 200 ms Coincidences required: 3 bands 27

28. Log N / Log S 1 hour of data 4x11

    minute 28

29. Status and outlook •  Trigger algorithm now runs 150 DM

    trials real-time •  Trigger parameters defined •  First test observations have been run (3x 4 hours) -  Handled triggers were all RFI events, apart from a trigger on B1919+21 •  To do: -  Run during remaining MSSS LBA observation (100 h) -  Run during MSSS HBA observations (full sky) -  Run during other observations? -  Make FRATS an easy add-on in LOFAR online system -  Further tuning of trigger algorithm -  Only use core-stations for incoherent beam •  TBB localisation (see talk by Emilio Enriquez) •  Trigger from ARTEMIS and other sources 29

30. Summary FRATS searches for dispersed millisecond pulses from various objects

    with a wide FoV parallel to other observations. Transient Buffer Boards see the whole sky for 1.3 seconds and thereby are a powerful tool to identify short duration signals First commissioning observations have been run 30

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32. Scattering Low DM, low scattering 32

33. Trigger parameters LBA bright small-band pulses observed or Scintillation effects?

    33 Subband group 38 MHz 54 MHz Sample number Detected pulses in each band