Andreas Horneffer

for the LOPES Collaboration

Detecting Radio Pulses from Air Showers with LOPES

LOPES(LOFAR Prototype Station)

prototype of a LOFAR station frequency range of 40 – 80 MHz set up at the KASCADE-Grande

site 10 antennas in the first phase, 30 antennas in the second phase

Goals: develop techniques to measure the radio emission from air showers determine the radiation mechanism of air showers calibrate the radio data with theoretical and experimental values from

an existing air shower array

Hardware of LOPES

Hardware of LOPES

LOPES-Antenna short dipole with “inverted vee shape” beamwidth 80°-120° (parallel/

perpendicular to dipole)

Hardware of LOPES

Receiver Module direct sampling of the radio

signal with minimal analog parts: amplifier, filter, AD-converter

sampling with 80 MSPS in the 2nd Nyquist domain of the AD-converter

Hardware of LOPES

Memory Buffer

aka. TIM-Module(Twin Input Module)

uses PC133-type memory memory for up to 6.1 seconds

per channel pre- and post-trigger

capability

Hardware of LOPES10

Clock & Trigger

distribution board

1 master & 3 slave boards master board generates

clock and accepts trigger slave boards distribute

clocks and trigger

LOPES: Setup & Status

30 antennas running at KASCADE

(10 antennas in first phase: LOPES10) triggered by large event (KASCADE) trigger

(10 out of 16 array clusters) offline or online correlation of KASCADE &

LOPES events KASCADE provides starting points for LOPES

air shower reconstruction core position of the air shower direction of the air shower size of the air shower

Averages 2500 – 3000 events per full day ca. 10 GByte uncompressed data per day ca. 3.6 TByte per year

Data Processing

steps of the data processing:1. instrumental delay correction from TV-phases

2. frequency dependent gain correction

3. filtering of narrow band interference

4. flagging of antennas

5. correction of trigger & instrumental delay

6. beam forming in the direction of the air shower

7. optimizing radius of curvature

8. quantification of peak parameters

Delay correction

TV-transmitter with picture- and two sound carriers relative phases between antennas lets us correct

for delay errors

delay corrections residual delays

Gain calibration

LNA (dark blue), cable (green), receiver Module (red), total (light blue)

measured the gain of the different parts “in the lab” combined all to a frequency dependent gain curve biggest uncertainty: match of antenna to LNA

Digital Filtering

raw data:

filtered data:blocksize: 128 samples blocksize: 64k samples

power spectrum:

Beamforming

Electric field and power after time shifting

Electric field and power before time shifting

Event Discrimination criteria for “good” events:

existence of a coherent pulse position in time of pulse uniform pulse height in all antennas

selection currently done manually

Good Event Bad Event

Example events 1

Antenna Data

Formed BeamPulse undetected by programGood Event Bad Event

LOPES10 Data

LOPES10 ran from January to September 2004 630 thousand events total

used selection for further study: KASCADE array processor didn’t fail distance of the core to the array center < 91m shower size (number of electrons) > 5e6 or

truncated muon number > 2e5 → 412 events

Detected Events 228 out of 412 events considered good Fraction of “good” to “bad” events increases with increasing

Muon number and increasing geomagnetic angle → fraction also increases with zenith angle

Dependencies: Geomagnetic Angle

Divided pulse height by muon number Fit results to the cosine of the geomagnetic angle Fit exponential decrease to distance

Divided pulse height by the results from previous fits. Added undetected events with height 2σ Only little dependency on electron number Power law is a good fit for muon number or energy

Dependencies: Size, Nµtrunc and Energy

Summary

LOPES measured radio pulses from air showers for the first time since 30 years

with digital filtering and beam forming these radio pulses can be measured even in a radio loud environment

measured radio pulse height depends on the angle to the geomagnetic field

radio pulse height correlates well with Nµ and energy and not so well with Ne

radio can give useful complementary information for air shower analysis additional value for energy and mass determination independent direction measurement position of the shower center