RADIO EMISSION OF COSMIC-RAY AIR SHOWERS AT THE SOUTH POLE AND A NEW ICETOP TRIGGER
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Abstract
The sources of highly energetic cosmic rays are still not fully understood. Better accuracy in composition measurement at different energies is essential to establish the origin of these energetic particles. IceTop is a cosmic-ray air-shower detector at the South Pole that is sensitive in the energy range of transition from the highest energy galactic sources to the extragalactic sources. However, IceTop is losing efficiency due to the continuous accumulation of snow above its ice-Cherenkov tanks. There is an ongoing effort to enhance IceTop with additional detectors, in particular, scintillator panels and radio antennas, with raisable stands. Radio antennas have better sensitivity to inclined air showers due to the stronger geomagnetic radio emission from such air showers. The coincident measurement of inclined cosmic-ray air showers with IceTop tanks and radio antennas can improve the measurement accuracy and, consequently, increase the sky coverage for mass-sensitive anisotropy studies using IceTop.
The polarization of radio emission from air showers is used to understand the contribution of the Askaryan and the geomagnetic radio emission mechanisms. The feasibility of using the direction of air showers and the relative Askaryan fraction of their radio emission in reconstructing the depth of shower maximum, $\mathrm{X}_{\mathrm{max}}$, which is sensitive to the mass of the cosmic-ray primary particle generating the air shower, is investigated. The theoretical $\mathrm{X}_{\mathrm{max}}$ resolution achievable with this technique is 20 - 40 g cm$^{-2}$, comparable to other techniques. Also, in an effort to improve the trigger efficiency of IceTop tanks to higher zenith angles, a new trigger was implemented with relaxed trigger conditions and validated with the first data from the South Pole. The improvement on the simulated full efficiency threshold compared to the standard trigger is about 0.2 in log10(E/eV) for vertical events and about 0.5 in log10(E/eV) for inclined events.