Andreas Horneffer

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
LOFAREffective Area

• 48/96 antennas per station
• inter-station baselines from 100m to 100km
• beam-forming at each station

5
LOFAR-CREnergy Ranges
Triggering on beam-formed data
Triggering on single-channel data
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VHECR-TriggeringStation View
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VHECR-TriggeringCentral Processor View
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HECR-TriggeringCentral Processor View
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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 gt µi k1si
• can be simplified to
• xi gt k2µi

10
Transient Buffer Boards

• one TBB for 16 channels
• one FPGA for 4 channels
• larger FPGA allows 3 IIR filters plus peak
  detection per channel

11
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

12
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

13
LOFAR Dynamic Spectrum
14
IIR Filtering

• No Filtering

15
IIR Filtering
Filter at 88 MHz (FM-transmitter)
16
IIR Filtering
Filter at 15 MHz (sw-band)
17
IIR Filtering
Filters at 15 MHz and 88 MHz
18
Filtering results

• filtering of FM-transmitter increases SNR
• short-wave band filtering increases stability of
  SNR

19
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

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LASALayout
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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