Recent Upgrades to TAROGE-M: Antarctic High-Mountain Radio Antenna Array for Detecting Near-Horizontal Ultra-High Energy Air Showers

TAROGE-M comprises autonomous radio antenna arrays operating at 180--450 MHz frequencies on top of $\sim2.7$ km-high Mt.~Melbourne in Antarctica, designed to detect near-horizontal ultra-high-energy (UHE) air showers with energies $>0.3$ EeV. The primary goal is to detect more of the so-called ANITA anomalous events --- air-shower-like events from below the horizon, which cannot be explained by tau neutrinos in the Standard Model, so as to address their origins. Like ANITA, TAROGE-M is at high altitude with a broad view toward the horizon, and operates in radio-quiet Antarctica with strong and near-vertical geomagnetic field which enhances the radio signal. However, TAROGE-M's mountain-based setup makes the design simpler, the duty cycle higher, and the expansion easier, and thus achieves a comparable exposure to ANITA experiments within a few station-years of operation. Since its initial detection of UHE cosmic rays (CRs) in 2020, TAROGE-M has undergone two major system upgrades. The first upgrade to a single station in February 2023 fulfilled a long-term operation extended until January 2024, including occasional operation powered by a small wind turbine in polar winter. It achieved $\sim195$-day live time, corresponding to a 56\% duty cycle. More detailed calibrations using drone-borne pulsers were conducted, complemented by the installation of a ground-based pulser for long-term calibration. The initial analysis result of 148-day data identified about 34 UHECR candidates, in agreement with simulations. With the second upgrade completed in January 2025, two stations are now operating with a more robust design to achieve reliable year-round functionality, and thus will enhance the search for ANITA anomalous events significantly. We present these system upgrades along with initial results from the CR search.