Andreas Horneffer

for the LOFAR Cosmic Ray KSP

Air Shower Measurements with LOFAR

Radboud University Nijmegen

Radboud University Nijmegen

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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

Radboud University Nijmegen

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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

Radboud University Nijmegen

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LOFAR-CREnergy Ranges

Triggering on single-channel data

Triggering on beam-formed data

Radboud University Nijmegen

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VHECR-TriggeringStation View

Radboud University Nijmegen

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VHECR-TriggeringCentral Processor View

Radboud University Nijmegen

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HECR-TriggeringCentral Processor View

Radboud University Nijmegen

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VHECR Trigger I

runs on the FPGAs of the TBBs pulse detection for single channels

1. digital Filtering of some RFI (IIR-filters)

2. peak detection

3. calculation of pulse parameters (position, height, width, sum, avg. before, avg. after)

peak detected if:

|xi| > μi + k1σi

can be simplified to:

|xi| > k2μi

Radboud University Nijmegen

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Transient Buffer Boards

one TBB for 16 channels

one FPGA for 4 channels

larger FPGA allows 3 IIR filters plus peak detection per channel

Radboud University Nijmegen

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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

Radboud University Nijmegen

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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

Radboud University Nijmegen

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LOFAR Dynamic Spectrum

Radboud University Nijmegen

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IIR Filtering

No Filtering

Radboud University Nijmegen

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IIR Filtering

Filter at 88 MHz (FM-transmitter)

Radboud University Nijmegen

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IIR Filtering

Filter at 15 MHz (sw-band)

Radboud University Nijmegen

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IIR Filtering

Filters at 15 MHz and 88 MHz

Radboud University Nijmegen

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Filtering results

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

Radboud University Nijmegen

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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

Radboud University Nijmegen

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LASALayout

Radboud University Nijmegen

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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