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
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
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
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!
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
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
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
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
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
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
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
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