Andreas Horneffer for the LOFAR Cosmic Ray KSP

1. Radboud University Nijmegen Air Shower Measurements with LOFAR Andreas Horneffer for the LOFAR Cosmic Ray KSP

2. LOFAR for Cosmic Rays • designed as an astronomical telescope not an air shower detector: • “small” stations with lots of antennas in a small area • different baselines between stations • consequences: • low effective area for the number of antennas • high sensitivity • very good calibration • this makes LOFAR an unique tool to study air showers: • Develop the method (triggering, reconstruction) • Understand the emission process • Air shower physics (new particles?) • Change galactic→extragalactic cosmic rays

3. Radio Signature of Air Showers • random arrival times and directions • can ignore (man made) pulses from the horizon • broad-band, short time pulse (~10ns) • limited illuminated area on the ground • depending on primary energy • curvature of radio front • similar (but not identical) to point source in few km height • coincident with other air shower signs • e.g. particle front

4. LOFAR-CREnergy Ranges Triggering on beam-formed data Triggering on single-channel data

5. VHECR-TriggeringStation View

6. VHECR-TriggeringCentral Processor View

7. HECR-TriggeringCentral Processor View

8. VHECR Trigger I • runs on the FPGAs of the TBBs • pulse detection for single channels • digital Filtering of some RFI (IIR-filters) • peak detection • calculation of pulse parameters (position, height, width, sum, avg. before, avg. after) • peak detected if: |xi| > μi + k1σi • can be simplified to: |xi| > k2μi

9. Transient Buffer Boards • one TBB for 16 channels • one FPGA for 4 channels • larger FPGA allows 3 IIR filters plus peak detection per channel

10. VHECR Trigger II • TBBs send “trigger messages” to station LCU • coincidence trigger at station level • filtering of “bad” pulses • coincidence detection • (direction fit) • data dump if pulse is found • stations send messages to CEP • dump more (all) stations for large events

11. LOFARTest Measurements • one 48 antenna station and three 16 antenna stations already in the field • two stations equipped with two TBBs each • 64 channels available • read out with low-level tools • dump to “raw dump” files • read in of raw-files or conversion to new file format

12. LOFAR Dynamic Spectrum

13. IIR Filtering No Filtering

14. IIR Filtering Filter at 88 MHz (FM-transmitter)

15. IIR Filtering Filter at 15 MHz (sw-band)

16. IIR Filtering Filters at 15 MHz and 88 MHz

17. Filtering results • filtering of FM-transmitter increases SNR • short-wave band filtering increases stability of SNR

18. LASALOFAR Air Shower Array • small particle detector array for triggering and additional data • main goal: proof that we indeed detect air showers • Needed to convince the cosmic ray community! • 5 stations with 4 scintillators each • around/inside the LOFAR “super-station” • main challenge: RFI shielding

19. LASALayout

20. Summary • LOFAR is an unique tool for air shower measurements: • high sensitivity • excellent calibration • measure in two modes: • HECR: trigger on beam-formed data • VHECR: trigger on single channel data • all digital triggering for VHECR: • filtering, peak detection, and pulse parameter determination in FPGA • coincidence trigger at station level • 2nd level coincidence to trigger additional stations • small particle detector array