arXiv subjects

Simon C. -C. Ho

Publications and source records attributed to Simon C. -C. Ho.

At least 19 recordsLinked to original sources

arXiv2026

Discovery of Two Consecutive Profile Change Events in the Millisecond Pulsar PSR J0437-4715

The closest and brightest millisecond pulsar (MSP), PSR J0437-4715, is a high-priority pulsar for precision timing experiments, including the Parkes Pulsar Timing Array (PPTA) project, where it is used for both pulsar timing and for polarization calibration. Using approximately seven years of observations obtained with the Ultra-Wideband Low-Frequency receiver on Murriyang, CSIRO's Parkes radio telescope, we investigate the long-term spectro-polarimetric variability of PSR J0437-4715. We report the discovery of two consecutive discrete profile change events exhibiting the same phase-localised morphological variations, the first such behaviour reported in any MSP. Both events affect three phase-localised regions of the pulse profile that exhibit coupled and anti-correlated temporal evolution. We also identified, and corrected for, systematic profile variability induced by polarization calibration errors arising from long-term drift of the polarimetric properties of the receiver. The profile change exhibits frequency-dependent evolution in total intensity, together with variations in linear polarization, position angle and fractional linear polarization. These results confirm a magnetospheric origin for the events rather than propagation effects caused by the interstellar medium, and provide potential new constraints on MSP emission models.

astro-ph.HE↗

arXiv2026

Statistical inference of fast radio burst environments using galaxy number density

Fast radio bursts (FRBs) are bright, millisecond-duration radio transients of unknown origin. They are categorized as repeaters and non-repeaters, possibly indicating distinct progenitor types. However, validating this distinction is difficult because of the limited number of localized FRBs. Large-scale galactic environments can provide insight into the nature of the host galaxies of FRBs and their progenitors. High-number-density regions are typically associated with old galaxies, whereas low-number-density regions are linked to young star-forming or less massive quiescent galaxies. In this study, we use galaxy number density to statistically assess the environments of 19 repeaters and 253 non-repeaters from CHIME Catalog 1, using galaxies from the WISE x PS1 catalog. A Kolmogorov-Smirnov (KS) test showed no significant difference between the two populations ($p_{\rm KS} = 0.673$). This result indicates that the statistical significance of the difference could depend on small-number statistics, highlighting the necessity of future FRB samples. Intriguingly, a comparison of FRBs with random galaxy fields suggests that FRBs may preferentially occur in underdense galactic environments, with a median $p$-value ($p_{\rm KS}$) of $2.84 \times 10^{-2}$ compared to random galaxy apertures.

astro-ph.GA↗

arXiv2026

A search for Fast Radio Bursts from globular clusters in M49 with FAST

The origins of fast radio bursts (FRBs) remain uncertain, although magnetars are a leading progenitor candidate. Because magnetars are thought to form primarily through core-collapse supernovae in young stellar populations, the discovery of FRB 20200120E in a globular cluster (GC) in the nearby galaxy M81 was unexpected given the ancient stellar populations of GCs. Expanding the sample of FRBs localised to nearby galaxies is therefore essential for testing FRB formation channels in old stellar environments. M49 (NGC 4472) is a nearby (~17 Mpc), radio-quiet giant elliptical galaxy in the Virgo cluster hosting about 7000 GCs, making it an ideal target for GC FRB searches. We conducted a 9-hour SnapShotCal observation of M49 using the Five-hundred-meter Aperture Spherical Telescope (FAST) 19-beam receiver, covering approximately 4230 GCs (2.1 hr per GC), and performed a comprehensive single-pulse search over a dispersion measure range of 0-5000 pc cm^-3. No unambiguous astrophysical FRBs were detected. The most significant trigger reached a post-processed signal-to-noise ratio of 8.6 sigma at a dispersion measure of 412.2 pc cm^-3, but is statistically consistent with thermal noise after accounting for the false-alarm rate. We derive a beam-averaged peak flux-density sensitivity of about 16.5 mJy (corresponding to a fluence limit of about 16.5 mJy ms for a 1 ms burst) and place an upper limit on the FRB occurrence rate of 4.7 x 10^-4 FRB GC^-1 hr^-1. Our non-detection constrains only bright bursts above this fluence threshold during the observing window.

astro-ph.HE↗

arXiv2026

Targeted search for eccentric supermassive binary black holes in OJ 287 and nearby galaxy clusters with PPTA DR3

We perform Bayesian targeted searches for continuous gravitational waves from eccentric supermassive binary black holes (SMBBHs) using the Parkes Pulsar Timing Array third data release (PPTA DR3). Six electromagnetically motivated sky directions are analyzed, including the blazar OJ~287 and five nearby galaxy clusters (Virgo, Fornax, Norma, Hercules, and Coma). No significant signals are found. For OJ 287, by explicitly incorporating orbital eccentricity (up to $e_0 = 0.8$) to robustly capture signal power spread across multiple harmonics, we constrain the total binary mass to $M_{\rm tot} < 5.25 \times 10^{10} M_{\odot}$ (95\% credible level). We also place upper limits on the chirp mass of potential SMBBHs residing in galaxy clusters. By combining these limits with independent black hole mass estimates, we place novel constraints on the allowed binary mass ratios for potential hosts such as M87 and NGC~4889. Specifically, our results exclude binaries with mass ratios $q \gtrsim 10^{-2}$ at around 10 nHz for these massive systems, effectively ruling out equal-mass black hole mergers in the sampled parameter space. These findings demonstrate the growing power of pulsar timing arrays to probe SMBBH populations.

astro-ph.GA↗

arXiv2026

A fast radio burst cyclone in technicolour: evidence of plasma lensing

Fast radio bursts (FRBs) are bright, energetic, radio pulses of extragalactic origin. A dichotomy has emerged in the population: some produce repeat bursts, while the majority do not. Most repeating sources only show rare repetitions, and none have been studied extensively over the wide bandwidths necessary to disentangle the physical processes that produce emission from distortions to bursts caused by intervening ionised gas. Here we present radio observations of the most active repeating source, FRB 20240114A. Using an ultrawideband receiving system, we have detected 5526 repetitions, revealing an extreme spectral and temporal variability in the burst emission. The bursts exhibit longer-term broadband variations in central emission frequency over multiple months, and narrowband bursts that have correlations in central frequencies on time scales of milliseconds to minutes. The spectral and temporal properties are consistent with the source undergoing magnification by foreground plasma lenses, potentially embedded in a turbulent circumsource medium. This extreme example highlights the role of plasma lenses in the observed properties of burst emission and can explain the diversity in activity and energetics of the entire FRB population.

astro-ph.HE↗

arXiv2026

Single-Pulse Correlations in PSR B0329+54: Implications for Radio Emission Zones

Individual radio pulses from a pulsar are directly linked to the underlying emission processes and the associated magnetic field geometry within its magnetosphere. Thus, single-pulse studies across frequencies can provide crucial insights into the physics of radio emission. Multiple studies have investigated single-pulse correlations in PSR B0329+54 with widely separated discrete frequencies, reporting the broadband nature of pulsar emission. However, understanding the frequency evolution of these correlations has been limited by poor frequency sampling, and the physical origin of these correlations remains unexplored. We present a detailed study of single-pulse correlations in PSR B0329+54 at low radio frequencies using the upgraded Giant Meterwave Radio Telescope (uGMRT), with well-sampled time series spanning 300-1460 MHz. We derived an inverted flux spectrum for this pulsar, with a turnover near 470 MHz. We used flux-calibrated and scintillation-corrected single pulses to study correlations across frequencies. Our results show that maximum correlations consistently occur near the longitude of the central component, with correlation strength exceeding 69\% for all frequency combinations, while outer components exhibit correlations above 46\%. These findings indicate very strong inter-frequency correlations, with no anticorrelations detected. No cross-component correlations were observed; only corresponding components correlate across frequencies. The longitudes of maximum correlation do not coincide with the intensity peaks of the average profile. We also examine how correlations vary with frequency at selected fiducial longitudes. The observations reported in this work favor curvature radiation from relativistic charge bunches in the pulsar plasma; however, reproducing the correlation curves along with spectra remains an open challenge.

astro-ph.HE↗

arXiv2025

JWST MIRI color classification of mid-infrared selected galaxies: MIRI color classification toward cosmic noon

We investigated the James Webb Space Telescope photometric color classification of mid-infrared (MIR) selected galaxies at high redshifts, toward cosmic noon. The aim of the present work is to obtain a z-dependent mid-infrared (MIR) photometric galaxy classification tool based on broad spectral emission and absorption lines using the JWST Mid-Infrared Instrument (MIRI) and its broadband filters. We used the largest Spitzer MIR spectral database to obtain synthetic photometry in the JWST/MIRI filters. We formed MIRI filter combinations to trace the strong polycyclic aromatic hydrocarbon (PAH) emission features and the 9.7 micron silicate feature in seven redshift windows from z = 0.25-2.10. Results. We present z-dependent MIRI color-color plots that separate active galactic nuclei (AGN), star-forming galaxies (SFGs), and silicate absorption-dominated galaxies up to z$\sim$2. We applied the photometric MIR colors to the largest ($\sim$34 arcmin square) MIRI survey called the Systematic Mid-infrared Instrument Legacy Extragalactic Survey (SMILES), to identify AGN, SFGs, and Si-absorption dominated galaxies out to substantial redshifts. Our JWST/MIRI SFGs sample includes galaxies with total IR luminosities of $10^{9.2} \sim 10^{11.9} L_{\odot}$ at 0.9 $\leq$z < 1.57. The majority of them are consistent with the z$\sim$1 main sequence. We also identified the first examples of z$\sim$1 galaxies with deep silicate absorption.

astro-ph.GA↗

arXiv2025

Machine learning classification of baseband data of CHIME FRBs

Fast Radio Bursts (FRBs) are bright millisecond radio pulses. Their origin is still unknown in the field of astronomy. A notable distinction among FRBs is that some sources repeat, while others appear to be non-repeating events. Interestingly, repeating FRBs tend to exhibit broader temporal widths and narrower spectral bandwidths compared to non-repeat events, suggesting they may arise from different physical mechanisms. However, current radio telescopes have limited coverage and sensitivity, which hinders a complete survey with continuous long-term monitoring. This issue makes it difficult to confirm repeat activity and potentially leads to misclassification of repeaters as non-repeaters; these are referred to as repeater candidates. To address this, machine learning techniques have emerged as a useful tool for classifying distinct FRB types in previous studies. In this study, we utilize the CHIME/FRB baseband catalog with three orders of magnitude better time resolution than the intensity catalog. Measured fluences are available in the baseband catalog, while only upper limits are reported in the intensity catalog. We apply machine learning to the baseband catalog to evaluate classification outcomes. We identify 15 repeater candidates among 122 non-repeating FRBs in the baseband catalog. Additionally, our classification identifies 31 sources previously categorized as repeater candidates as non-repeaters, highlighting a significant difference from the prior work. Of these repeater candidates, 14 overlap with previous findings, while 1 is newly identified in this work. Notably, one of our candidates was confirmed as a repeater by CHIME/FRB. Follow-up observations for the 14 candidates are highly encouraged.

astro-ph.HE↗

arXiv2025

Photometrically Selected Protocluster Candidates at z~9-10 in the JWST COSMOS-Web field

High-redshift protoclusters are crucial for understanding the formation of galaxy clusters and the evolution of galaxies in dense environments. The James Webb Space Telescope (JWST), with its unprecedented near-infrared sensitivity, enables the first exploration of protoclusters beyond $z>$10. Among JWST surveys, COSMOS-Web Data Release 0.5 offers the largest area $\sim$0.27 deg$^2$, making it an optimal field for protocluster searches. In this study, we searched for protoclusters at $z\sim$9-10 using 366 F115W dropout galaxies. We evaluated the reliability of our photometric redshift by validation tests with the JADES DR3 spectroscopic sample, obtaining the likelihood of falsely identifying interlopers as $\sim25\%$. Overdensities ($δ$) are computed by weighting galaxy positions with their photometric redshift probability density functions (PDF), using a 2.5 cMpc aperture and a redshift slice of $\pm$0.5. We selected the most promising core galaxies of protocluster candidate galaxies with an overdensity greater than the 95th percentile of the distribution of 366 F115W dropout galaxies. The member galaxies are then linked within an angular separation of 7.5 cMpc to the core galaxies, finding seven protocluster candidates. These seven protocluster candidates have inferred halo masses of $M_{\text{halo}} \sim 10^{11} M_{\odot}$. The detection of such overdensities at these redshifts provides a critical test for current cosmological simulations. However, confirming these candidates and distinguishing them from low-redshift dusty star-forming galaxies or Balmer-break galaxies will require follow-up near-infrared spectroscopic observations.

astro-ph.GA↗

arXiv2025

Brown dwarf number density in the JWST COSMOS-Web field

Brown dwarfs are failed stars with very low mass (13 to 75 $M_J$), and an effective temperature lower than 2500 K. Thus, they play a key role in understanding the gap in the mass function between stars and planets. However, due to their faint nature, previous searches are inevitably limited to the solar neighbourhood (20 pc). To improve our knowledge of the low mass part of the initial stellar mass function and the star formation history of the Milky Way, it is crucial to find more distant brown dwarfs. Using James Webb Space Telescope (JWST) COSMOS-Web data, this study seeks to enhance our comprehension of the physical characteristics of brown dwarfs situated at a distance of kpc scale. The exceptional sensitivity of the JWST enables the detection of brown dwarfs that are up to 100 times more distant than those discovered in the earlier all-sky infrared surveys. The large area coverage of the JWST COSMOS-Web survey allows us to find more distant brown dwarfs than earlier JWST studies with smaller area coverages. To capture prominent water absorption features around 2.7 $μ$m, we apply two colour criteria, F115W-F277W+1 0.9. We then select point sources by CLASS_STAR, FLUX_RADIUS, and SPREAD_MODEL criteria. Faint sources are visually checked to exclude possibly extended sources. We conduct SED fitting and MCMC simulations to determine their physical properties and associated uncertainties. Our search reveals 25 T-dwarf and 2 Y-dwarf candidates, more than any previous JWST brown dwarf searches. They are located from 0.3 kpc to 4 kpc away from the Earth. The cumulative number count of our brown dwarf candidates is consistent with the prediction from a standard double exponential model. Three of our brown dwarf candidates were detected by HST, with transverse velocities $12\pm5$ km s$^{-1}$, $12\pm4$ km s$^{-1}$, and $17\pm6$ km s$^{-1}$.

astro-ph.SR↗

arXiv2025

Detection of over 37,000 giant pulses per hour from PSR J1823$-$3021A with UHF baseband observations from MeerKAT

Giant pulses (GPs) occur in high magnetic-field millisecond pulsars (MSPs) and young Crab-like pulsars. Motivated by the fast radio bursts (FRBs) discovered in a globular cluster (GC) in the M81, we undertook baseband observations of PSR J1823$-$3021A, the most active GP emitter in a GC with the MeerKAT UHF band receiver (544-1088 MHz). The steep spectral index of the pulsar yields a GP rate of over 37,000 GPs/hr with $S/N>7$, significantly higher than the 3000 GPs/hr rate detected by Abbate et al. 2020 with the L-band (856-1712 MHz) receiver. Similarly to Abbate et al 2020, we find that the GPs are (1) strongly clustered in 2 particular phases of its rotation, (2) well described by a power-law in terms of energies, (3) typically broadband, and have steep spectral indices of $\approx-3$. Although the integrated pulse profile is not significantly polarised ($<1\%$ linear and $<3\%$ circular), one of the brightest GPs displays notable polarisation of $7\%$ (linear) and $8\%$ (circular). The high-time resolution data reveals the GPs have a range of single-peak and multi-peak morphologies, including GPs with three distinct peaks. For the first time, we measured the temporal scattering of the pulsar using 49 bright, narrow, single-pulse GPs, obtaining a mean value of $5.5\pm0.6$ $μ$s at 1 GHz. The distinct periodicity and low polarisation of GPs differentiate them from typical FRBs, although potential quasi-periodicity substructures in some GPs may suggest a connection to magnetars/FRBs.

astro-ph.HE↗

arXiv2025

A Far-Infrared Search for Planet Nine Using AKARI All-Sky Survey

An unusual orbital element clustering of Kuiper belt objects (KBOs) has been observed. The most promising dynamic solution is the presence of a giant planet in the outer Solar system, Planet Nine. However, due to its extreme distance, intensive searches in optical have not been successful. We aim to find Planet Nine in the far-infrared, where it has the peak of the black body radiation, using the most sensitive all-sky far-infrared survey to date, AKARI. In contrast to optical searches, where the energy of reflected sunlight decreases by $d^{4}$, thermal radiation in the infrared decreases with the square of the heliocentric distance $d^{2}$. We search for moving objects in the AKARI Single Scan Detection List. We select sources from a promising region suggested by an N-body simulation from Millholland and Laughlin 2017: $30^{\circ}<$ R.A. $<50^{\circ}$ and $-20^{\circ}<$ Dec. $<20^{\circ}$. Known sources are excluded by cross-matching AKARI sources with 9 optical and infrared catalogues. Furthermore, we select sources with small background strength to avoid sources in the cirrus. Since Planet Nine is stationary in a timescale of hours but moves on a monthly scale, our primary strategy is to select slowly moving objects that are stationary in 24 hours but not in six months, using multiple single scans by AKARI. The selected slowly moving AKARI sources are scrutinised for potential contamination from cosmic rays. Our analysis reveals two possible Planet Nine candidates whose positions and flux are within the theoretical prediction ranges. These candidates warrant further investigation through follow-up observations to confirm the existence and properties of Planet Nine.

astro-ph.EP↗

arXiv2025

Do they repeat? Monitoring 36 non-repeating FRBs with FAST

The origin of fast radio bursts (FRBs), highly energetic, millisecond-duration radio pulses originating from beyond our galaxy, remains unknown. Observationally, FRBs are classified as non-repeating or repeating, however, this classification is complicated by limited observing time and sensitivity constraints, which may result in some repeating FRBs being misidentified as non-repeating. To address this issue, we adopt both empirical and machine-learning techniques from previous studies to identify candidates that may have been misclassified. We conducted follow-up observations of 36 such candidates, each observed for 10 minutes using the Five-hundred-meter Aperture Spherical Telescope (FAST). No radio bursts exceeding a signal-to-noise ratio of 7 were detected, with a typical 7 sigma fluence limit of ~0.013 Jy ms. We constrain the repetition rates of these sources using two statistical models of FRB occurrence. Combining our FAST non-detections with prior observations, we derive upper limits on the repetition rates of ~$10^{-2.6}$-$10^{-0.22}$ hr$^{-1}$ under a Poisson process, and ~$10^{-2.3}$-$10^{-0.25}$ hr$^{-1}$ under a Weibull process. This work presents one of the most stringent upper limits on FRB repetition rates to date, based on a sample size five times larger than those used in previous studies.

astro-ph.HE↗

arXiv2025

Decoding the cosmological baryonic fluctuations using localized fast radio bursts

Aims: The enigma of the missing baryons poses a prominent and unresolved problem in astronomy. Dispersion measures (DM) serve as a distinctive observable of fast radio bursts (FRBs). They quantify the electron column density along each line of sight and reveal the missing baryons that are described in the Macquart (DM-z) relation. The scatter of this relation is anticipated to be caused by the variation in the cosmic structure. This is not yet statistically confirmed, however. We present statistical evidence that the cosmological baryons fluctuate. Methods: We measured the foreground galaxy number densities around 14 and 13 localized FRBs with the WISE-PS1-STRM and WISE x SCOS photometric redshift galaxy catalog, respectively. The foreground galaxy number densities were determined through a comparison with measured random apertures with a radius of 1 Mpc. Results: We found a positive correlation between the excess of DM that is contributed by the medium outside galaxies (DM_cosmic) and the foreground galaxy number density. The correlation is strong and statistically significant, with median Pearson coefficients of 0.6 and 0.6 and median p-values of 0.012 and 0.032 for the galaxy catalogs, respectively, as calculated with Monte Carlo simulations. Conclusions: Our findings indicate that the baryonic matter density outside galaxies exceeds its cosmic average along the line of sight to regions with an excess galaxy density, but there are fewer baryons along the line of sight to low-density regions. This is statistical evidence that the ionized baryons fluctuate cosmologically on a characteristic scale of $\lesssim$6 Mpc.

astro-ph.CO↗

arXiv2025

A Search for Planet Nine with IRAS and AKARI Data

The outer solar system is theoretically predicted to harbour an undiscovered planet, often referred to as P9. Simulations suggest that its gravitational influence could explain the unusual clustering of minor bodies in the Kuiper Belt. However, no observational evidence for P9 has been found so far, as its predicted orbit lies far beyond Neptune, where it reflects only a faint amount of Sunlight. This work aims to find P9 candidates by taking advantage of two far-infrared all-sky surveys, which are IRAS and AKARI. The epochs of these two surveys were separated by 23 years, which is large enough to detect the ~3'/year orbital motion of P9. We use a dedicated AKARI Far-Infrared point source list for our P9 search - AKARI Monthly Unconfirmed Source List, which includes sources detected repeatedly only in hours timescale, but not after months. We search for objects that moved slowly between IRAS and AKARI detections given in the catalogues. First, we estimated the expected flux and orbital motion of P9 by assuming its mass, distance, and effective temperature to ensure it can be detected by IRAS and AKARI, then applied the positional and flux selection criteria to narrow down the number of sources from the catalogues. Next, we produced all possible candidate pairs whose angular separations were limited between 42' and 69.6', corresponding to the heliocentric distance range of 500 - 700 AU and the mass range of 7 - 17 Earth masses. There are 13 pairs obtained after the selection criteria. After image inspection, we found one good candidate, of which the IRAS source is absent from the same coordinate in the AKARI image after 23 years and vice versa. However, AKARI and IRAS detections are not enough to determine the full orbit of this candidate. This issue leads to the need for follow-up observations, which will determine the Keplerian motion of our candidate.

astro-ph.EP↗

arXiv2025

Machine learning based Photometric Redshifts for Galaxies in the North Ecliptic Pole Wide field: catalogs of spectroscopic and photometric redshifts

We perform an MMT/Hectospec redshift survey of the North Ecliptic Pole Wide (NEPW) field covering 5.4 square degrees, and use it to estimate the photometric redshifts for the sources without spectroscopic redshifts. By combining 2572 newly measured redshifts from our survey with existing data from the literature, we create a large sample of 4421 galaxies with spectroscopic redshifts in the NEPW field. Using this sample, we estimate photometric redshifts of 77755 sources in the band-merged catalog of the NEPW field with a random forest model. The estimated photometric redshifts are generally consistent with the spectroscopic redshifts, with a dispersion of 0.028, an outlier fraction of 7.3%, and a bias of -0.01. We find that the standard deviation of the prediction from each decision tree in the random forest model can be used to infer the fraction of catastrophic outliers and the measurement uncertainties. We test various combinations of input observables, including colors and magnitude uncertainties, and find that the details of these various combinations do not change the prediction accuracy much. As a result, we provide a catalog of 77755 sources in the NEPW field, which includes both spectroscopic and photometric redshifts up to z~2. This dataset has significant legacy value for studies in the NEPW region, especially with upcoming space missions such as JWST, Euclid, and SPHEREx.

astro-ph.CO↗

arXiv2025

Retracing the Cold Plasma Dispersion Law in Pulsar B0329+54: New Insights into Frequency-Dependent Dispersion Measures

Multiple studies have investigated potential frequency-dependent dispersion measures (DM) in PSR B0329+54, with sensitivities at levels of $10^{-3} \, \text{pc} \, \text{cm}^{-3}$ or higher, using frequencies below 1 GHz. Utilizing the extensive bandwidth of the upgraded Giant Meterwave Radio Telescope, we conducted simultaneous observations of this pulsar across a frequency range of 300 to 1460 MHz. Our observations reveal a distinct point in the pulse profile of PSR B0329+54 that appears to align remarkably well with the cold-plasma dispersion law, resulting in a unique measured DM across the entire frequency range. In contrast, using times of arrival (ToAs) from widely adopted pulsar timing techniques (e.g., FFTFIT)-leads to frequency-dependent DMs. We investigated the potential causes of these frequency-dependent DMs in this pulsar and their relationship with the underlying magnetic field geometry corresponding to the radio emission. Our study reveals that all frequencies in the range 300-1460 MHz originate from a region no larger than 204 km, and the dipolar magnetic-field geometry model indicates that the emission region is centered at $\sim$800 km from the star. This is the tightest constraint on the size of the emission region reported so far for PSR B0329+54 at the given frequencies, and it is at least five times more stringent than the existing emission height constraints based on the dipolar geometry model.

astro-ph.HE↗

arXiv2024

Constraining the Hubble constant with scattering in host galaxies of fast radio bursts

Measuring the Hubble constant (H$_0$) is one of the most important missions in astronomy. Nevertheless, recent studies exhibit differences between the employed methods. Fast radio bursts (FRBs) are coherent radio transients with large dispersion measures (DM) with a duration of milliseconds. DM$_{\rm IGM}$, DM in the intergalactic medium (IGM), could open a new avenue for probing H$_0$. However, it has been challenging to separate DM contributions from different components (i.e., the IGM and the host galaxy plasma), and this hampers the accurate measurements of DM$_{\rm IGM}$ and hence H$_0$. We adopted a method to overcome this problem by using the temporal scattering of the FRB pulses due to the propagation effect through the host galaxy plasma (scattering time). The scattering-inferred DM in a host galaxy improves the estimate of DM$_{\rm IGM}$, which in turn leads to a better constraint on H$_0$. In previous studies, a certain value or distribution has conventionally been assumed of the dispersion measure in host galaxies (DM$_{\rm h}$). We compared this method with ours by generating 100 mock FRBs, and we found that our method reduces the systematic (statistical) error of H$_0$ by 9.1% (1%) compared to the previous method. We applied our method to 30 localized FRB sources with both scattering and spectroscopic redshift measurements to constrain H$_0$. Our result is H$_0$=74$_{-7.2}^{+7.5}$ km s$^{-1}$ Mpc$^{-1}$, where the central value prefers the value obtained from local measurements over the cosmic microwave background. We also measured DM$_{\rm h}$ with a median value of $103^{+68}_{-48}$ pc cm$^{-3}$. The reduction in systematic error is comparable to the Hubble tension ($\sim10$%). Combined with the fact that more localized FRBs will become available, our result indicates that our method can be used to address the Hubble tension using future FRB samples.

astro-ph.CO↗