Radboud University Nijmegen Air Shower Measurements with LOFAR
Radboud University Nijmegen Air Shower Measurements with LOFAR Andreas Horneffer for the LOFAR-CR Team
LOFAR A new kind of Radio Telescope n n n Digital radio interferometer for the frequency range of 10 - 270 MHz Array of 36+ Dutch and 8+ international stations of 48 to 96 simple antennas Two antenna types: l l n Radboud University Nijmegen Low band (10 -90 MHz) High band (110 -270 MHz) Fully digital: received waves are digitized and processed in computers: l l Streaming data for astronomy (interferometry and tied-array) Transient Buffer Boards (TBB) for cosmic rays and other short transients 2
LOFAR for Cosmic Rays n LOFAR works in the frequency range of interest for cosmic ray measurements: l l n n 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 l l n Radboud University Nijmegen Can store the full waveform information for >1 s Beam-forming after a trigger gives full sensitivity LOPES has demonstrated the ability of such a system to detect air showers 3
LOFAR Status n n 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 l l n Radboud University Nijmegen 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 12 th June 4
LOFAR Roll Out Radboud University Nijmegen http: //www. astron. nl/~heald/lofar. Status. Map. html http: //www. astron. nl/radio-observatory/astronomers/current-status 5
LOFAR Opening 12 th June Radboud University Nijmegen 6
Queens Helicopter Radboud University Nijmegen 7
LOFAR-CR Energy Ranges Radboud University Nijmegen Air Shower detection Triggering on beam -formed on data Triggering singlechannel data Looking at the Moon 8
LOFAR for Air Showers n Designed as an astronomical telescope not an air shower detector: l l n “Small” stations with lots of antennas in a small area Different baselines between stations Consequences: l l l n Radboud University Nijmegen Low effective area for the number of antennas High sensitivity Very good calibration This makes LOFAR an unique tool to study air showers: l l l Develop the method (triggering, reconstruction) Understand the emission process (lateral distribution, spectrum, curvature) Air shower physics (new particles? ) 9
Superterp Radboud University Nijmegen ca. 400 m 76 m 10
Radio Signature of Air Showers n Random arrival times and directions l n n Depending on primary energy Curvature of radio front l n Can ignore (man made) pulses from the horizon Broad-band, short time pulse (~10 ns) Limited illuminated area on the ground l n Radboud University Nijmegen Similar (but not identical) to point source in few km height Coincident with other air shower signs l E. g. particle front 11
Transient Buffer Boards Radboud University Nijmegen External trigger 12
Transient Buffer Boards Radboud University Nijmegen G. trigger External trigger Local Control Unit Trigger 13
LOFAR TBB-Status n n TBB hard- and firmware is working and stable TBB DAQ software: l l n Radboud University Nijmegen 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: l l l Several modules done (e. g. read-in, skymapper) Algorithm development in Python Analysis with custom made C++ applications or Python scripts 14
VHECR Trigger n 1. Three level triggering scheme: Pulse detection for single channels n n 2. n n Detect coincidences of many (all? ) channels Select good air shower candidates Dump local data for those Large/marginal event detection at CEP n n n Online processing of the data stream from each dipole Send trigger message for each detected pulse Coincidence trigger at station level n 3. Radboud University Nijmegen 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 15
1 st level VHECR Trigger n n Runs on the FPGAs of the TBBs Pulse detection for single channels 1. 2. 3. n n Radboud University Nijmegen 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| > k 2μi Peak detected if several (nearly) consecutive samples above threshold 16
Noise Level (during construction) Radboud University Nijmegen Blue: No filter Green: 15 MHz Red: 88 MHz 17
TBB Trigger Rate Radboud University Nijmegen 18
2 nd level VHECR Trigger n n TBBs send “trigger messages” to station LCU Coincidence trigger at station level l n Radboud University Nijmegen Filtering of “bad” pulses Coincidence detection Direction fit → tbd → implemented → first version After trigger: dump 1 ms worth of data → 1 st vers. (1 k. Hz frequency resolution) 19
Direction Reconstruction Radboud University Nijmegen by A. Corstanje 20
Radio Triggered Event after beam-forming Radboud University Nijmegen 21
Skymap of Triggered Radboud University Nijmegen Event 22
Skymap from LOPES data Radboud University Nijmegen 23
LORA LOFAR Radboud Air Shower Array n n Small particle detector array for triggering and additional data 5 stations with 4 scintillators each Around/inside the LOFAR “super-station” Status: l l n Radboud University Nijmegen Hardware and DAQ done Currently working on detector calibration Deployment: l l First station: ASAP Full array: September Worked on by S. Thoudam 24
Timeline n LOFAR VHECR: l l n Radboud University Nijmegen First air shower measurements: soon Stable (piggy-back) observations: August/September Analysis pipeline: September First science results: this year LORA deployment: l l First station: ASAP Full array: September 25
Summary n LOFAR is an unique tool for air shower measurements: l l n High sensitivity Excellent calibration All digital triggering for VHECR: l n Radboud University Nijmegen 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 26
Spare Slides Radboud University Nijmegen 27
Skymap of LOFAR data with 200 m roc Radboud University Nijmegen 28
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