1. Andreas Horneffer for the LOFAR-CR Team
Radboud University Nijmegen
Air Shower Measurements
with LOFAR
Andreas Horneffer
for the LOFAR-CR Team

2. LOFAR A new kind of Radio Telescope
Digital radio interferometer for the frequency range of MHz
Array of 36+ Dutch and 8+ international stations of 48 to 96 simple antennas
Two antenna types:
Low band (10-90 MHz)
High band ( MHz)
Fully digital: received waves are digitized and processed in computers:
Streaming data for astronomy (interferometry and tied-array)
Transient Buffer Boards (TBB) for cosmic rays and other short transients

3. LOFAR for Cosmic Rays
LOFAR works in the frequency range of interest for cosmic ray measurements:
Air showers: 30 – 90 MHz
Radio flashes from the moon: 110 – 180 MHz
Two orders of magnitude improvement in resolution and sensitivity over other telescopes
Fully digital design gives “look back” capability
Can store the full waveform information for >1s
Beam-forming after a trigger gives full sensitivity
LOPES has demonstrated the ability of such a system to detect air showers 3

4. LOFAR Status
Roll out going on: 24 NL & 2 D stations ready, to be finished this year)
Standard imaging, Pulsar and VHECR are first observing modes to be commissioned
Automated pipeline for uncalibrated images
High-quality images with lots of fiddeling
Several pulsar observations done
About to do first air shower test observations
Big opening ceremony 12th June

5. LOFAR Roll Out http://www.astron.nl/~heald/lofarStatusMap.html

6. LOFAR Opening 12th June

7. Queens Helicopter

8. LOFAR-CR Energy Ranges
Air Shower detection
Triggering on beam-formed data
Triggering on single-channel data
Looking at the Moon

9. LOFAR for Air Showers
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 (lateral distribution, spectrum, curvature)
Air shower physics (new particles?)

10. Superterp
ca. 400m
76m

11. 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

12. Transient Buffer Boards
External trigger 12

13. Transient Buffer Boards
G. trigger
External trigger
Local Control Unit
Trigger 13

14. LOFAR TBB-Status TBB hard- and firmware is working and stable
TBB DAQ software:
Scripts for setup and simultaneous dumping of data
Inclusion into general DAQ system has started
First radio triggered data available
Interface to calibration data still missing
Analysis software:
Several modules done (e.g. read-in, skymapper)
Algorithm development in Python
Analysis with custom made C++ applications or Python scripts

15. VHECR Trigger Three level triggering scheme:
Pulse detection for single channels
Online processing of the data stream from each dipole
Send trigger message for each detected pulse
Coincidence trigger at station level
Detect coincidences of many (all?) channels
Select good air shower candidates
Dump local data for those
Large/marginal event detection at CEP
Dump more (all) stations for large events
Detect multi-station events that are sub-threshold in single stations
Final decision: Air Shower ↔ RFI in post-processing

16. 1st level VHECR Trigger Implemented and working
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)
Single sample threshold: |xi| > k2μi
Peak detected if several (nearly) consecutive samples above threshold
Implemented
and working

17. Noise Level (during construction)
Blue: No filter
Green: 15MHz
Red: 88MHz

18. TBB Trigger Rate

19. 2nd level VHECR Trigger TBBs send “trigger messages” to station LCU
Coincidence trigger at station level
Filtering of “bad” pulses → tbd
Coincidence detection → implemented
Direction fit → first version
After trigger: dump 1ms worth of data → 1st vers. (1kHz frequency resolution)

20. Direction Reconstruction
by A. Corstanje

21. Radio Triggered Event after beam-forming

22. Skymap of Triggered Event

23. Skymap from LOPES data

24. LORA LOFAR Radboud Air Shower Array
Small particle detector array for triggering and additional data
5 stations with 4 scintillators each
Around/inside the LOFAR “super-station”
Status:
Hardware and DAQ done
Currently working on detector calibration
Deployment:
First station: ASAP
Full array: September
Worked on by S. Thoudam

25. Timeline LOFAR VHECR: LORA deployment:
First air shower measurements: soon
Stable (piggy-back) observations: August/September
Analysis pipeline: September
First science results: this year
LORA deployment:
First station: ASAP
Full array: September

26. Summary LOFAR is an unique tool for air shower measurements:
High sensitivity
Excellent calibration
All digital triggering for VHECR:
Filtering, peak detection, and pulse parameter determination in FPGA → tested!
Coincidence trigger at station level → working version
Central coincidence stage to trigger additional stations
Small particle detector array
First cosmic rays measured this year

27. Spare Slides

28. Skymap of LOFAR data with 200m roc