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

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

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]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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