andreas horneffer for the lopes collaboration detecting radio pulses from air showers with lopes
TRANSCRIPT
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