The effect of the atmospheric refractive index on the radio signal of extensive air showers

Abstract

For the interpretation of measurements of radio emission from extensive air showers, an important systematic uncertainty arises from natural variations of the atmospheric refractive index $n$. At a given altitude, the refractivity $N=10^6(n-1)$ can have relative variations on the order of $10\%$ depending on temperature, humidity, and air pressure. Typical corrections to be applied to $N$ are about $4\%$. Using CoREAS simulations of radio emission from air showers, we have evaluated the effect of varying $N$ on measurements of the depth of shower maximum $X_{\max }$. For an observation band of 30 to 80 MHz, a difference of $4\%$ in refractivity gives rise to a systematic error in the inferred $X_{\max }$ between 3.5 and 11 $g/c{\mathrm{m}}^2$, for proton showers with zenith angles ranging from 15 to 50 degrees. At higher frequencies, from 120 to 250 MHz, the offset ranges from 10 to 22 $g/c{\mathrm{m}}^2$. These offsets were found to be proportional to the geometric distance to $X_{\max }$. We have compared the results to a simple model based on the Cherenkov angle. For the 120 to 250 MHz band, the model is in qualitative agreement with the simulations. In typical circumstances, we find a slight decrease in $X_{\max }$ compared to the default refractivity treatment in CoREAS. While this is within commonly treated systematic uncertainties, accounting for it explicitly improves the accuracy of $X_{\max }$ measurements.

arXiv comment13 pages, 5 figures. Accepted for publication in Astroparticle Physics

References in corpus (23)

• LOFAR: The LOw-Frequency ARray
• Measurements of the Cosmic Ray Composition with Air Shower Experiments
• Depth of Maximum of Air-Shower Profiles at the Pierre Auger Observatory: Measurements at Energies above 10^17.8 eV
• The Atacama Cosmology Telescope: Temperature and Gravitational Lensing Power Spectrum Measurements from Three Seasons of Data
• Simulating radio emission from air showers with CoREAS
• Radio detection of cosmic ray air showers in the digital era
• A large light-mass component of cosmic rays at 10^{17} - 10^{17.5} eV from radio observations
• A method for high precision reconstruction of air shower Xmax using two-dimensional radio intensity profiles
• Observation of Ultra-high-energy Cosmic Rays with the ANITA Balloon-borne Radio Interferometer
• Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory
• Detecting cosmic rays with the LOFAR radio telescope
• Description of Atmospheric Conditions at the Pierre Auger Observatory using the Global Data Assimilation System (GDAS)
• Coherent Cherenkov Radiation from Cosmic-Ray-Induced Air Showers
• A Realistic Treatment of Geomagnetic Cherenkov Radiation from Cosmic Ray Air Showers
• Polarized radio emission from extensive air showers measured with LOFAR
• The shape of the radio wavefront of extensive air showers as measured with LOFAR
• Measuring a Cherenkov ring in the radio emission from air showers at 110-190 MHz with LOFAR
• Radio measurements of the energy and the depth of the shower maximum of cosmic-ray air showers by Tunka-Rex
• The radio emission pattern of air showers as measured with LOFAR - a tool for the reconstruction of the energy and the shower maximum
• First Experimental Characterization of Microwave Emission from Cosmic Ray Air Showers
• The air shower maximum probed by Cherenkov effects from radio emission
• Macroscopic Model of Geomagnetic-Radiation from Air Showers, II
• Simulations of detector arrays and the impact of atmospheric parameters

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• Computing the electric field from Extensive Air Showers using a realistic description of the atmosphere
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