An update on real-time triggering on beamformed data

Sander ter Veen
LOFAR TKP Meeting, Amsterdam, June 2011

Transcript

1. Update TKP meeting Amsterdam June 2011 FRATS: Real-time triggering on Fast Radio Transients with LOFAR Sander ter Veen, Pim Schellart, Clancy James, Heino Falcke for the LOFAR Transients and Cosmic Ray KSP Radboud University Nijmegen
2. 29-06-11 2 If I may look tired... LIGHTNING!
3. 29-06-11 3 Science • Real-time serendipity search for bright dispersed millisecond pulses – Pulsars (Giant pulses) – RRATS – Flare stars – Exoplanets
4. 29-06-11 4 Real-time detection principle Station beam Dipole/Tile data Dipole/Tile data Dipole/Tile data TBB buffers Station beam Dipole/Tile data Dipole/Tile data Dipole/Tile data TBB buffers Incoherent Or Coherent Beam Station beam Trigger algorithm Obtain data Obtain data
5. 29-06-11 5 Offline data analysis Station beam(s) Dipole/Tile data Dipole/Tile data Dipole/Tile data TBB buffers Station beam(s) Dipole/Tile data Dipole/Tile data Dipole/Tile data TBB buffers Many Coherent Beams (high time- resolution images) Station beam Search algorithm Accurate Position (down to few arcsec or less)
6. 29-06-11 6 Detection philosophy • Commensal observation mode – Large sky/time coverage for rare events • Offline data analysis similar to Cosmic Ray data analysis • No detailed LOFAR follow up needed to determine position • More accurate position helps Multi-WL • Real-time: no extra processing time
7. 29-06-11 7 Trigger method 20 ms 195kHz • 1 subband with 64 channels G iant Pulse from C rab pulsar DM=5, 190 MHz-150 MHz Δt = 0.36 s 190 Mhz-110 Mhz Δt = 1.12 s
8. 29-06-11 8 Trigger method 20 ms 195kHz 20 blocks • 1 subband with 64 channels Correct for dispersed time Check for coincidence Require K out of N subbands G iant Pulse from C rab pulsar
9. 29-06-11 9 Trigger Method • Take beamformed data in power • Divide total bandwidth in several bands • Dedisperse every band and look for a peak • Peak: Power > N * std + mean • Check for coincidences between the bands
10. 29-06-11 10 Status: principle proven • Crab Giant pulse Trigger Re-detection
11. 29-06-11 11 Status: principle proven • Crab Giant pulse Trigger Precise localisation
12. 29-06-11 12 TBB trigger • “External” trigger via ssh • Last year shell scripts • This year python library • PyQt GUI • Next few months: MAC/SAS implementation • UDP trigger protocol
13. 29-06-11 13 Large scale test • LOFAR Pulsar Pilot Survey (dec 2010) • 7 incoherent beams, 6.8 Mhz, 8 divisions • 255 pointings taken so far • Real-time triggering on part of the pointings • Off-line analysis on other pointings • No TBB data dumps • 30 DM trials between [10,25]
14. 29-06-11 14 The good news • Found 7 pulses from pulsar B0834+06
15. 29-06-11 15 The bad news • Many false triggers obs21756 (R) obs21781 obs21783 obs21786 obs21757 obs21796 0 50 100 150 200 250 triggers
16. 29-06-11 16 Check: DM=0 signal? obs21756 (R) obs21781 obs21783 obs21786 obs21757 obs21796 0 50 100 150 200 250 triggers no RFI within 50 samples no RFI within 100 samples no RFI within 500 samples
17. 29-06-11 17 Check: Multiple beam trigger? obs21756 (R) obs21781 obs21783 obs21786 obs21757 obs21796 0 50 100 150 200 250 triggers no 3 beam within 50 samples no 3 beam within 100 samples no 3 beam within 500 samples
18. 29-06-11 18 Check: Combine both? obs21756 (R) obs21781 obs21783 obs21786 obs21757 obs21796 0 50 100 150 200 250 triggers within 50 samples within 100 samples within 500 samples
19. 29-06-11 19 RFI excision • DM=0 with multi-beam check is efficient but not yet perfect • Need to check data after trigger (step / long duration RFI )
20. 29-06-11 20 Observing plans • MSSS: commensal incoherent beam • LOTAS: add additional stations – (19 Coherent beams pulsar survey) • Needs option to select certain stations for beamforming • All-sky low DM LBA survey
21. 29-06-11 21 All sky Low DM LBA • Low DM: Distinguishable at low freq • LBA: Wide beam, fast survey • All -sky: arc of beams in declination • Scan one RA • Move to next RA • Pointing duration depends on bandwidth • New beam center at FWHM
22. 29-06-11 22 Observation parameters • More bandwidth by more 24hr runs or less beam overlap Freq (MHz) Nr Dec Bandwidth (MHz) Repointing time Integration time Max DM (1.3 s) 10 6 8 55 52 0.02 20 12 4 27 24 0.3 30 18 2.7 18 15 1.6 40 24 2 14 11 5 50 29 1.7 11 8 11.5 60 35 1.4 9 6 24.2 70 42 1.2 8 5 44.7 80 47 1.0 7 4 80.2
23. 29-06-11 23 Summary • Principle proven: FRATS works! • Need to develop RFI discrimination • Optimize search algorithm (more DMs) • Test / run LBA survey and commensal to other data • Test / develop further TBB identification