ANITAIV

ANITA-IV refers to the fourth long-duration balloon mission in NASA’s Antarctic Impulsive Transient Antenna (ANITA) program. The mission built on a series of balloon-borne radio detectors designed to observe nanosecond radio impulses produced by high-energy particle cascades in Antarctic ice or in the atmosphere. ANITA-IV conducted a circumpolar flight over Antarctica, carrying a polar array of horn antennas that detected broad-band radio signals in the 200–1200 MHz range, triggered by impulsive events characteristic of the Askaryan effect and extensive air showers from cosmic rays.

The instrument combined a high-gain, wide-field antenna system with fast data acquisition and calibration subsystems to operate in the extreme Antarctic environment. By monitoring large areas of ice and the surrounding atmosphere from stratospheric altitude, ANITA-IV aimed to detect ultra-high-energy neutrinos with energies above roughly 10^18 eV, testing models of cosmogenic neutrino production and propagation, and to study primary cosmic rays through their radio signatures.

Results and impact: ANITA-IV did not yield a confirmed detection of ultra-high-energy neutrinos during its flight, but it improved upper limits on the diffuse neutrino flux at the highest energies and contributed a substantial dataset of radio-detection events from both ice and air showers. The mission continued to address anomalous upward-going event candidates observed in earlier ANITA flights, contributing to the ongoing discussion of potential beyond-Standard-Model explanations while maintaining compatibility with standard physics within current uncertainties. The experience and data from ANITA-IV informed the design of future balloon-based radio detectors and enhanced the broader program of high-energy astroparticle physics in Antarctica.