arXiv subjects

Obinna Modilim

Publications and source records attributed to Obinna Modilim.

3 recordsLinked to original sources

arXiv2026

The 256-antenna Coherent All-Sky Monitor

Radio astronomy is uniquely coupled to exponential trends in computation because the optics (cross-correlation, beamforming, and imaging) and spectrometry (i.e. channelization) can now be done digitally. Inexpensive analog-to-digital converters (ADCs) can sample signals from large numbers of antennas and graphics processing units (GPUs) allow us to coherently process wide-field radio data in real time, motivating large-$N$ aperture arrays at moderate cost. We describe the 256-antenna Coherent All-Sky Monitor (CASM-256), a dense aperture array operating at 375-500\,MHz, currently being deployed at the Owens Valley Radio Observatory (OVRO) in Big Pine, California. The large field-of-view (FoV$\sim10^4$\,deg$^2$) and point-source sensitivity of CASM-256 will allow it to detect local Universe fast radio bursts (FRBs). The nearby sample is ideal for unveiling the physical origin of FRBs, measuring the baryonic content of nearby galaxy halos, and discovering prompt multi-wavelength and multi-messenger counterparts to FRBs. CASM will search for fast transients in the Milky Way such as FRB analogs, pulsar giant pulses, and the new source class known as long-period radio transients. We describe the instrument and present on-sky data from the first two dozen antennas, including an operational real-time GPU based FRB search pipeline. We emphasize the scalability of the concept and describe paths to a future CASM array with tens of thousands of antennas that could detect one million FRBs.

astro-ph.IM↗

arXiv2025

CHIME/FRB Discovery of an Unusual Circularly Polarized Long-Period Radio Transient with an Accelerating Spin Period

We report the discovery of CHIME J1634+44, a Long Period Radio Transient (LPT) unique for two aspects: it is the first known LPT to emit fully circularly polarized radio bursts, and it is the first LPT with a significant spin-up. Given that high circular polarization ($>90$\%) has been observed in FRB~20201124A and in some giant pulses of PSR~B1937+21, we discuss the implications of the high circular polarization of CHIME J1634+44 and conclude its emission mechanism is likely to be ``pulsar-like''. While CHIME J1634+44 has a pulse period of 841 s, its burst arrival patterns are indicative of a secondary 4206 s period, probably associated with binary activity. The timing properties suggest it has a significantly negative period derivative of $\dot{P}=-9.03(0.11)\times 10^{-12}$ s s$^{-1}$. Few systems have been known to spin-up, most notably transitional millisecond pulsars and cataclysmic binaries, both of which seem unlikely progenitors for CHIME J1634+44. If the period was only associated with the spin of the object, then the spin up is likely generated by accretion of material from a companion. If, however, the radio pulse period and the orbital period are locked, as appears to be the case for two other LPTs, the spin up of CHIME J1634+44 could be driven by gravitational wave radiation.

astro-ph.HE↗

arXiv2023

Host Galaxies for Four Nearby CHIME/FRB Sources and the Local Universe FRB Host Galaxy Population

We present the host galaxies of four apparently non-repeating fast radio bursts (FRBs), FRBs 20181223C, 20190418A, 20191220A, and 20190425A, reported in the first Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB) catalog. Our selection of these FRBs is based on a planned hypothesis testing framework where we search all CHIME/FRB Catalog-1 events that have low extragalactic dispersion measure (< 100 pc cm$^{-3}$), with high Galactic latitude (|b| > 10$\deg$) and saved baseband data. We associate the selected FRBs to galaxies with moderate to high star-formation rates located at redshifts between 0.027 and 0.071. We also search for possible multi-messenger counterparts, including persistent compact radio and gravitational wave (GW) sources, and find none. Utilizing the four FRB hosts from this study along with the hosts of 14 published local Universe FRBs (z < 0.1) with robust host association, we conduct an FRB host demographics analysis. We find all 18 local Universe FRB hosts in our sample to be spirals (or late-type galaxies), including the host of FRB 20220509G, which was previously reported to be elliptical. Using this observation, we scrutinize proposed FRB source formation channels and argue that core-collapse supernovae are likely the dominant channel to form FRB progenitors. Moreover, we infer no significant difference in the host properties of repeating and apparently non-repeating FRBs in our local Universe FRB host sample. Finally, we find the burst rates of these four apparently non-repeating FRBs to be consistent with those of the sample of localized repeating FRBs observed by CHIME/FRB. Therefore, we encourage further monitoring of these FRBs with more sensitive radio telescopes.

astro-ph.HE↗