arXiv subjects

Hiroto Masaoka

Publications and source records attributed to Hiroto Masaoka.

3 recordsLinked to original sources

arXiv2026

Design and Commissioning of the BURSTT-256 Main Antenna Array for the Fast Radio Burst Survey in the Local Universe

The Bustling Universe Radio Survey Telescope in Taiwan (BURSTT) is a radio interferometer array designed for surveying fast radio bursts (FRBs) in the nearby Universe with a wide instantaneous field of view (FoV) of $\approx$6000 deg$^2$ and precisely localizing them with sub-arcsecond angular resolution. The first phase of BURSTT, BURSTT-256, consists of a main antenna array comprising 256 log-periodic dipole antennas (LPDAs) observing at 400-800 MHz for real-time beamforming and FRB search, currently with 256 beams covering $\approx$ 3200 deg$^2$ FoV, together with several smaller outrigger stations with 16-64 antennas and separated by $\mathcal{O}(10^2 - 10^3)$ km baselines for joint observations to localize FRBs using very-long baseline interferometry. This work presents the design, deployment, and commissioning of the BURSTT-256 main array, including site selection, radio-frequency (RF) background characterization, receiver antenna array and RF front-end, as well as real-time, factorized digital beamforming backend that currently generates 256 beams. The system's on-sky performance, sensitivity, and beamforming fidelity have been calibrated through observations of bright celestial calibrators. The antenna array in the initial phase using commercial LPDAs has a system equivalent flux density of $\approx$11 kJy, and is expected to achieve $\approx$4 kJy using custom-design LPDAs after optimization in late 2026. BURSTT-256 serves as a critical pathfinder for future expansion of the array to 2048 elements and beyond, operating at 300-700 MHz with $\approx$6000 deg$^2$ FoV. It establishes the framework required to discover and localize nearby FRBs with sub-arcsecond precision. By substantially increasing the number of well-localized nearby FRBs, BURSTT will facilitate multi-wavelength and multi-messenger counterpart identification, helping to unveil the elusive origin of FRBs.

astro-ph.IM↗

arXiv2026

VLBI Astrometry of Magnetars

The origin of the strongest magnetic fields in the Universe, i.e., the origin of magnetars, is a longstanding question. An enhanced dynamo effect in an irregular supernova explosion is a possible origin, which implies a stronger kick velocity and a higher proper motion of the magnetar compared to those of ordinary pulsars as well as an irregular morphology of the host supernova remnant (SNR). However, this hypothesis is not well studied yet, because there is a lack of precise measurement of the proper motion of magnetar and of identification of the host SNR. VLBI astrometry of magnetars is a unique tool to examine the hypothesis. In this chapter, we introduce the MONSTER (Monitoring Observations of the Neutron Stars That Evolve Rapidly) Project. SKA-VLBI's unprecedented sensitivity and the highest angular resolution will allow us to dramatically expand the survey volume in which we can measure the proper motion of magnetars within a radio outburst period of a few months.

astro-ph.HE↗

arXiv2026

Constraints on the Physical Association between ICECAT1 Neutrinos and Fast Radio Bursts Using the Second CHIME/FRB Catalogue

We present a search for neutrino counterparts to fast radio bursts (FRBs) using temporal and spatial cross-matching between the Second CHIME/FRB catalogue and the IceCube high-energy alert-track catalogue ICECAT1. Because current FRB--neutrino models do not provide a unique consensus on emission ordering, our primary significance test adopts a two-sided, order-agnostic temporal hypothesis. The analysis accounts for declination-dependent CHIME/FRB exposure and the look-elsewhere effect across multiple trials. No statistically significant FRB--neutrino association is found. The most significant pair is FRB\,20190630C--IC\,190629A, with a post-trial probability of $p=0.076$ ($1.43σ$), consistent with a chance coincidence. Within our statistical framework, a detectable physical association would require a time offset shorter than $\sim256$~s at $3σ$ or $\sim63$~ms at $5σ$. Using a population-level stacking analysis, we derive 90\% upper limits on the neutrino-to-radio luminosity ratio of FRBs, $ξ\lesssim 10^{8}-10^{11}$ for neutrino power-law spectral indices $γ=1.0-3.0$. These limits improve upon previous constraints by approximately two orders of magnitude and represent the most stringent bounds from FRB--neutrino coincidence searches to date. Although the current limits remain above the predictions of most magnetar-based models, they begin to constrain scenarios involving exceptionally efficient hadronic energy dissipation.

astro-ph.HE↗