study of the cosmic ray radio emission pattern at …laura rossetto – lofar science workshop –...
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Study of the cosmic ray Study of the cosmic ray radio emission pattern radio emission pattern
at ground level with LOFARat ground level with LOFAR
Laura RossettoLaura Rossettoon behalf of the Cosmic Ray Key Science Projecton behalf of the Cosmic Ray Key Science Project
LOFAR Science Workshop, Assen, June 2nd – 3rd 2015
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
A. Nelles et al., 2014, Astroparticle Physics, 60, 13-24
The footprint of the radio signal The footprint of the radio signal
22
v
Xv x B
v x (v x B)
v = shower axisB = Earth magnetic field vector
B
What is the shape of the radio signal footprint?
A. Nelles et al., 2015, Journal of Cosmology and Astroparticle Physics 05, 018
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Simulation study Simulation study
33
Particle production → CORSIKA 7.400 with FLUKA 2011.2b and QGSJETII.04
Radio emission → CoREAS
Energy = 1016 – 1018.8 eV, zenith = 3° – 55°
Antenna layout → star–shape pattern in the shower plane
On the ground level
Plane perpendicular to the shower axis
Nor
th [m]
East [m]
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Simulation study Simulation study
44
Two-dimensional Gaussian distribution
P → total power of the integrated signalx' → coordinate along the v x B directiony' → coordinate along the v x (v x B) directionX
+ →location parameter along v x B
Y+ → location parameter along v x (v x B)
σ+ → width parameter
A+ → amplitude parameter
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Simulation study Simulation study
55
Two-dimensional Gaussian distribution
“Bean shape” → combination of two-dimensional Gaussian distributions
→ The two Gaussians are shifted and subtracted from each others ( A
+ > A
– )
→ 9 free parameters
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Simulation study Simulation study
66
Fit results for a single simulated shower
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Simulation study Simulation study
66
Fit results for a single simulated shower
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen 77
· simulation– linear fit
A± ∝ n
charged ∝ E2
· simulation– linear fit
Simulation study Simulation study
For coherent emission
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen 88
· simulation– second order pol. fit
· simulation– second order pol. fit
Width of the distribution σ± is proportional to the distance of the shower maximum from ground level
Simulation study Simulation study
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen 99
Shift of the positive and negative Gaussian w.r.t. the shower core is proportional to the azimuth→ combination of the geomagnetic and charge excess effect in the radio emission
· simulation– fit
· simulation– fit
Simulation study Simulation study
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Data analysis: reduction of free parameters Data analysis: reduction of free parameters
1010
The number of free parameters can be reduced by considering correlations between parameters → the maximum reduction is obtained by using only 4 free parameters
XC
→location parameter along v x B
YC
→ location parameter along v x (v x B)
σ+ → width parameter
A+ → amplitude parameter
→ C0 , C
1 and C
2 constant
→ C3 binned for zenith angle
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Parametrization applied to DATA Parametrization applied to DATA
1111
→ Fit applied to ALL LBA LOFAR data
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Parametrization applied to DATA Parametrization applied to DATA
1111
→ Fit applied to ALL LBA LOFAR data
→ Good quality fit
→ events with θ < 15º show slightly less good fit
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Reconstruction of shower parameters Reconstruction of shower parameters
1212
Shower core position
Cross-check with LORA detectors
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Reconstruction of shower parameters Reconstruction of shower parameters
1313
Cross-check with LORA detectors
Cross-check with MC simulations
Energy of primary particle
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Reconstruction of shower parameters Reconstruction of shower parameters
1414
Width parameter σ+ proportional to 1/cos(θ)
Shower maximum
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Reconstruction of shower parameters Reconstruction of shower parameters
1515
What does it happen at frequencies around 100 MHz?
A. Nelles et al., 2015, Astroparticle Physics, 65, 11-21
→ Signature of a relativistic time compression
→ the radio emission is amplified at a specific angle w.r.t. the shower axis
→ “Cherenkov ring” has a diameter of about 100 m and is dominant at frequencies above 100 MHz
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Reconstruction of shower parameters Reconstruction of shower parameters
1616
→ Fit applied to HBA data as well
→ amplified ring structure at about 100 m from shower axis
→ ring size sensitive to the depth of the shower maximum
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Laura Rossetto – LOFAR Science Workshop – June 2Laura Rossetto – LOFAR Science Workshop – June 2ndnd – 3 – 3rdrd 2015, Assen 2015, Assen
Conclusions Conclusions
1717
Simulation study of the radio emission signal at ground level → double Gaussian distribution with minimum 4 free parameters → parameters related to shower properties
The parametrization function has been used to fit ALL LOFAR data → good agreement for both LBA and HBA data
Independent method for measuring the energy, depth of the shower maximum, position of the shower axis at ground level
A. Nelles et al., 2014, Astroparticle Physics, 60, 13-24
A. Nelles et al., 2015, Journal of Cosmology and Astroparticle Physics 05, 018
A. Nelles et al., 2015, Astroparticle Physics, 65, 11-21