1. Andreas Horneffer for the LOFAR Cosmic Ray KSP
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. LOFAR Core Layout 48/96 antennas per station
inter-station baselines from 100m to 100km
beam-forming at each station

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

5. VHECR-Triggering Station View

6. VHECR-Triggering Central Processor View

7. HECR-Triggering Central Processor View

8. VHECR Trigger 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)
coincidence trigger at station level
filtering of “bad” pulses
coincidence detection
(direction fit)
data dump if pulse is found
dump more (all) stations for large events

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. LOFAR Test Measurements
one 48 antenna station and three 16 antenna stations already in the field
two stations equipped with two TBBs each
largest problem currently: control software and stability

11. LOFAR Dynamic Spectrum

12. IIR Filtering
No Filtering

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

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

15. IIR Filtering
Filters at 15 MHz and 88 MHz

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

17. LASA LOFAR Air Shower Array
small particle detector array for triggering and additional data
main goal: proof that we indeed detect air showers
4 or 5 stations with 4 scintillators each
around/inside the LOFAR “super-station”
main challenge: RFI shielding

18. LASA Layout

19. 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