showers with LOFAR Laura Rossetto 35 th ICRC July 13 th 2017 - - PowerPoint PPT Presentation

Characterisation of radio frequency spectrum emitted by high energy air showers with LOFAR

35th ICRC – July 13th 2017 – Bexco, Busan, South Korea

Laura Rossetto

Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

th 2017, Busan

2017, Busan

The The LO LOw w F Frequency requency AR ARray ray

2 2

• M. van Haarlem et al., A&A 556, A2, 2013

→ 24 stations (~ 2 km radius) located in Northern Netherlands form the LOFAR core → 6 stations (~ 320 m diameter) form the LOFAR “Superterp” → 50 stations in Northern Europe: The Netherlands, France, Germany, Ireland, Poland, Sweden, and UK

The The LO LOw w F Frequency requency AR ARray ray

3 3 Each Dutch station has: → 96 Low Band Antennas (LBAs) frequency = 10 – 90 MHz → two orthogonal dipole arms with

• rientation NE – SW and NW – SE

→ 48 High Band Antennas (HBAs) frequency = 110 – 240 MHz Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

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2017, Busan 3 3

The The LO LOw w F Frequency requency AR ARray ray

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

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ICRC – July 13th

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Posters id 402 id 413

• S. Thoudam et al., Nucl. Inst. Meth. A 767, 339, 2014

→ the six central stations are instrumented with 20 scintillators which give the main trigger for Cosmic Ray event detection → cosmic ray E = 1016 – 1018 eV

Geomagnetic synchrotron emission

→ separation of charged particles due to the geomagnetic field

Charge excess emission

→ negative charge excess produced at the shower front

Radio emission processes of EAS Radio emission processes of EAS

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• A. Nelles et al., JCAP 05, 18, 2015
• O. Scholten et al., PRD 94, 103010, 2016

Frequency spectrum study Frequency spectrum study

GOALS:

→ to characterise the pattern of radio signals in the frequency–domain → to improve the reconstruction of the showers, i.e. position of the shower axis at ground, energy and mass composition of primary particle

ANALYSIS:

→ Analysis applied to data collected by LOFAR since 2011 and CORSIKA/CoREAS simulated showers

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Dmax = 3.6 km Dmax = 5.9 km Dmax = 6.1 km

Frequency spectrum study: the method Frequency spectrum study: the method

• 1. Signal in the time–domain has been converted to the frequency–domain by applying a

Fast Fourier Transform on Δt = 128 samples = 640 ns (1 sample = 5 ns)

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Frequency spectrum study: the method Frequency spectrum study: the method

• 1. Signal in the time–domain has been converted to the frequency–domain by applying a

Fast Fourier Transform on Δt = 128 samples = 640 ns (1 sample = 5 ns)

• 2. |FFT|2

Signal → evaluated on Δt = [ t0 – 240 ns , t0 + 400 ns ] where t0 = time of the pulse–peak

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

th 2017, Busan

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Frequency spectrum study: the method Frequency spectrum study: the method

• 1. Signal in the time–domain has been converted to the frequency–domain by applying a

Fast Fourier Transform on Δt = 128 samples = 640 ns (1 sample = 5 ns)

• 2. |FFT|2

Signal → evaluated on Δt = [ t0 – 240 ns , t0 + 400 ns ] where t0 = time of the pulse–peak

• 3. |FFT|2

Background → evaluated on 400 sub-windows outside the pulse region

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

th 2017, Busan

2017, Busan 7 7

Frequency spectrum study: the method Frequency spectrum study: the method

• 1. Signal in the time–domain has been converted to the frequency–domain by applying a

Fast Fourier Transform on Δt = 128 samples = 640 ns (1 sample = 5 ns)

• 2. |FFT|2

Signal → evaluated on Δt = [ t0 – 240 ns , t0 + 400 ns ] where t0 = time of the pulse–peak

• 3. |FFT|2

Background → evaluated on 400 sub-windows outside the pulse region

• 4. |FFT|2

= |FFT|2 Signal – |FFT|2 Background

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

th 2017, Busan

2017, Busan 7 7

Frequency spectrum study: the method Frequency spectrum study: the method

• 1. Signal in the time–domain has been converted to the frequency–domain by applying a

Fast Fourier Transform on Δt = 128 samples = 640 ns (1 sample = 5 ns)

• 2. |FFT|2

Signal → evaluated on Δt = [ t0 – 240 ns , t0 + 400 ns ] where t0 = time of the pulse–peak

• 3. |FFT|2

Background → evaluated on 400 sub-windows outside the pulse region

• 4. |FFT|2

= |FFT|2 Signal – |FFT|2 Background

• 5. linear fit applied to log10|FFT|2 in the range ν = 33 – 70 MHz

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

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ICRC – July 13th

th 2017, Busan

2017, Busan 7 7 log10|FFT|2 = a + slope · ν

Real data results Real data results

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2017, Busan 8 8 → Event selection criteria: 1) at least 1 station with half antennas having signal > 10 σ → 142 events 2) events with at least 10 antennas with

| FFT(νi ) | 2 > RMS ( | FFT(νi ) | 2

B )

→ 103 events

→ Linear–fit applied to all antennas

• f each selected event

Real data results – Shower axis distance Real data results – Shower axis distance

3 3 Laura Rossetto – 35 Laura Rossetto – 35th

th ICRC – July 13

ICRC – July 13th

th 2017, Busan

2017, Busan 9 9 → Event selection criteria: 1) at least 1 station with half antennas having signal > 10 σ → 142 events 2) events with at least 10 antennas with

| FFT(νi ) | 2 > RMS ( | FFT(νi ) | 2

B )

→ 103 events

→ Linear–fit applied to all antennas

• f each selected event

E = 1.7 · 1017 eV Xmax = 757 g/cm2

→ the slope–parameter shows a parabolic distribution as function of distance to the shower axis

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ICRC – July 13th

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→ comparison to simulations → maximum around 100 m in agreement with the Cherenkov ring region

• syst. unc.

Xmax (sim) = 755 g/cm2 Xmax = 757 g/cm2 → Event selection criteria: 1) at least 1 station with half antennas having signal > 10 σ → 142 events 2) events with at least 10 antennas with

| FFT(νi ) | 2 > RMS ( | FFT(νi ) | 2

B )

→ 103 events

→ Linear–fit applied to all antennas

• f each selected event

Real data results – Shower axis distance Real data results – Shower axis distance

Real data results – D Real data results – Dmax

max correlation

correlation

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Dmax (km) Dmax (km)

33/103 events 22/103 events

→ the slope parameter depends on the geometrical distance of the observer from Xmax (i.e. Dmax) → at fix distances from the shower axis:

slope (D max)= α 1+exp(−β⋅ D max)−γ

Slope at 180 m ( MHz –2 ) Slope at 220 m ( MHz –2 )

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ICRC – July 13th

th 2017, Busan

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Conclusions Conclusions

• Radio frequency spectrum has been studied in the range 30 – 70 MHz
• linear–fit applied to real data detected by LOFAR since 2011, and to

corresponding CORSIKA/CoREAS simulated showers

• clear dependence of the frequency spectrum as function of distance to the

shower axis has been obtained → this can be used as an independent method to reconstruct the position of the shower axis at ground

• At fixed distances from the shower axis, the frequency spectrum depends

also on the geometrical distance to Xmax → independent method for Xmax reconstruction

Poster id 402