arXiv subjects

Victoria M. Kaspi

Publications and source records attributed to Victoria M. Kaspi.

At least 19 recordsLinked to original sources

arXiv2026

The CHIME/FRB Outriggers: Commissioning the Hat Creek Outrigger and an Updated Calibration Scheme for Mitigating RFI

This work presents commissioning of the Hat Creek Outrigger (HCO), a dual-polarization 256-element radio interferometer that is part of the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) Outrigger project. Driven by a complex radio-frequency interference (RFI) environment that consistently contaminates $\sim40\%$ of HCO's usable bandwidth, we implement an improved calibration scheme using Gaussian Process Regression to recover complex gain solutions over RFI contaminated channels. To validate our method, we test the performance of the array using known transients and continuum sources over relevant timescales used for fast-transient research ($\lesssim$ seconds). We find that our updated calibration scheme results in a $\sim1.69\times~\mathrm{to}~1.87\times$ improvement in the array's point-source sensitivity, while simultaneously maintaining noise properties consistent with thermal statistics. As a result, we find that the array performs consistently within theoretical expectations across $\gtrsim80\%$ of HCO's bandpass. We further observe an improvement in the interferometric performance after applying recently developed spatial filtering techniques for RFI mitigation, which rely on accurate calibration solutions for effective removal of unwanted interference. We conclude that our approach provides a valid framework for improving calibration solutions over RFI contaminated channels for large-$N$ interferometric arrays more broadly. Our work motivates future development of more sophisticated techniques to recover astrophysical information in RFI-contaminated channels, departing from the historical practice of discarding them outright.

astro-ph.IM↗

arXiv2026

No Measurable Changes in Radio and X-ray Emission Surrounding Glitches in the Young Pulsar PSR J2229+6114

We present our first result from an ongoing pulsar glitch monitoring campaign at the Canadian Hydrogen Intensity Mapping Experiment (CHIME), in which we analyzed the radio and X-ray emission surrounding four glitches in PSR~J2229+6114. Using daily CHIME observations, we detected a glitch in PSR~J2229+6114 in near-real time and triggered an X-ray follow-up with the Nuclear Spectroscopic Telescope Array (NuSTAR) two days after the glitch. We identified three additional glitch events in archival CHIME/Pulsar observations that coincided with an independent X-ray observing campaign with the Neutron star Interior Composition Explorer (NICER).. Our data show there is no measurable change in the source's X-ray and radio emission during the four glitch events, in stark contrast to the post-glitch activity in high-magnetic-field, rotation-powered pulsars (RPPs), which have been observed to exhibit magnetar-like X-ray outbursts immediately after large glitches. Those high-magnetic-field (high-$B$) RPPs are considered transitional objects between ordinary RPPs and magnetars, thereby leading to a unifying neutron star model in which the inferred dipolar surface magnetic field strength serves as a unifying parameter. However, such a model remains challenged, in part, by the lack of constraints near the low-$B$ end of the high-$B$ regime, and our result provides additional evidence that magnetar-like post-glitch activity is likely more common among high-$B$ RPPs.

astro-ph.HE↗

arXiv2026

Generalized Non-linear Bayesian Pulsar Timing with Enterprise

In this study, we use the Bayesian methods in the Enterprise package to examine the fully general parameterization of pulsar timing models in tandem with noise. We investigate four pulsars, PSR J1600$-$3053, PSR J2043+1711, PSR J0740+6620, and PSR J1640+2224, through the lens of Bayesian timing. These four are selected as they are well-studied, but exhibit interesting characteristics under the lens of Bayesian timing. Our new pulsar mass constraints (medians and 68\% confidence intervals) for our fully general non-linear Bayesian timing models are $m_{\mathrm{p}}=1.6(1)~\mathrm{M}_{\odot}$ for PSR J2043+1711 and $m_{\mathrm{p}}=2.3^{+0.9}_{-0.7}~\mathrm{M}_{\odot}$ for PSR J1600$-$3053 both using the NANOGrav 12.5-yr data release, and $m_{\mathrm{p}}=2.06(6)~\mathrm{M}_{\odot}$ for PSR J0740+6620 using the data from Fonseca, et al., 2021. We investigate the effects on placing physical priors on timing model parameters, including restricting the upper limit on the pulsar mass for PSR J1640+2224, which has a mass often estimated to be greater than $3~\mathrm{M}_{\odot}$. We find \ark{that restricting the allowed sampling space of the pulsar mass for PSR J1640+2224 to} $m_{\mathrm{p}}<3~\mathrm{M}_{\odot}$ results in a pulsar mass of $m_{\mathrm{p}}=2.2(5)~\mathrm{M}_{\odot}$ for PSR J1640+2224 using the NANOGrav 12.5-yr data release. For the first time, we find evidence for intrinsic red noise in PSR J2043+1711. We show how fully general Bayesian timing can better model the interplay of the intrinsic noise and the timing parameters.

astro-ph.HE↗

arXiv2026

Evidence for Enhancement in the Rate of Fast Radio Bursts Toward Galaxy Clusters

Massive galaxy clusters can introduce gravitational lensing and populations of suppressed star formation member galaxies into the line of sight, potentially changing the distribution of observable sources toward them from that of the average sky. As a result, Fast Radio Bursts (FRBs) aligned with galaxy clusters can provide a unique window into parameter spaces of the FRB population that other lines of sight do not afford. In this study, we demonstrate that the second CHIME/FRB baseband catalog contains FRBs emitted from within or behind clusters identified from the latest DECaLS data release; we isolate a sample of 26 FRBs where this is likely, including one repeating FRB and two FRBs that intersect the Coma cluster. Comparing our results against a range of simulated FRB populations, we conclude that the number of these associations represents a $3σ$ rate enhancement toward galaxy clusters, constituting $1.4\pm0.4\%$ of the FRBs detected in the second CHIME/FRB baseband catalog. We suggest that this enhancement is caused by an equal proportion of member galaxies hosting additional FRBs, and gravitational lensing magnifying background sources. We demonstrate that such contributions are sensitive to alternative progenitor channels and high redshift evolution in the FRB population, providing a future avenue for constraining these features. Considering the redshifts and masses of the associated clusters, we identify FRB 20211113A, which is aligned with the strong gravitational lens Abell 2218 as a potential lensed candidate for further consideration.

astro-ph.CO↗

arXiv2026

CHIME/Slow overview and pilot survey: A new backend to search for second-duration radio transients with the CHIME telescope

We present an overview of CHIME/Slow, a real-time transient search backend under development to search for second-duration radio transients using the CHIME telescope, and results obtained from a pilot survey carried out using the prototype version of the search pipeline. The prototype CHIME/Slow pipeline was tested on archival data obtained in December 2022, January 2023 and February 2023 with a total on-sky time of 17 days with an instantaneous Field of View (FoV) of $\sim$13 deg$^2$ . In this pilot survey, we detected nine bursts, one from a new non-repeating source and eight from the known hyperactive repeating source FRB 20220912A. Out of these nine bursts, two bursts from the repeater were not detected by CHIME/FRB, while the non-repeater was detected in the side-lobe of a beam in the CHIME/FRB exhibiting shorter pulse width and narrower bandwidth compared to the CHIME/Slow detection. Here we report properties of the bursts, discuss the sensitivity and completeness of the current version of the CHIME/Slow pipeline, and outline future development to improve its performance. Finally, based on these results, we report the all-sky rate (95% credible region) of radio transients with pulse widths between 16 ms to 5 s, fluence above 5 Jy ms and observing frequency of 600 MHz to be between 184 and 4556 bursts sky$^{-1}$ day$^{-1}$.

astro-ph.IM↗

arXiv2026

Debiasing the Observed Fast Radio Burst Population with the CHIME/FRB Selection Function

The recent release of CHIME/FRB Catalog~2 provides the largest sample to date with which to investigate the intrinsic distributions of fast radio bursts (FRBs). Leveraging an expanded campaign of 587,367 synethetic bursts injected into the live CHIME/FRB search pipeline, we perform a population analysis of the fluence, scattering timescale, pulse width, and dispersion measure distributions of Catalog~2 FRBs. We first infer the intrinsic population using a resampling-based framework that accounts for instrumental selection effects following previous CHIME/FRB population studies. A central goal of this work is to constrain the intrinsic distribution of scattering timescales, that remained weakly constrained in Catalog~1 owing to limited statistics at moderate and large scattering times ($τ\gtrsim 10\,\mathrm{ms}$ at 600~MHz) and sparse injection coverage in this regime. Second, we construct an explicit multidimensional selection function by training a logistic regression model on the injected events. This model estimates the detection probability as a function of FRB observable properties, including higher-order interaction terms. We incorporate this selection function into a simulation-based inference framework to refine the inferred intrinsic scattering-timescale distribution. We find evidence for a slight downturn in the intrinsic FRB scattering timescale distribution, though a flat or slightly rising distribution cannot be ruled out, that is further supported through a comparison with the higher-frequency scattering timescale distribution observed by Commensal Real-time ASKAP Fast Transients (CRAFT) survey.

astro-ph.HE↗

arXiv2026

Discovery of 30 Repeating Fast Radio Burst Sources and Uniform Population Statistics of 80 Repeating Sources from CHIME/FRB

We present 30 newly discovered repeating fast radio burst (FRB) sources from the second catalog of bursts detected by the FRB backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME/FRB). These repeaters have extragalactic dispersion measures (DMs) spanning $99.4-1446.0\ \text{pc cm}^{-3}$ and burst rates between $10^{-5.7}$ and $10^{-0.5}$ hr$^{-1}$ scaled to a fluence threshold of 5 Jy ms. We report evidence of monotonic, linear DM variations in four repeaters on years-long timescales. The newly discovered sources bring CHIME/FRB's total number of observed repeating FRBs to 80, 79 of which were discovered by CHIME/FRB, between 2018 July 25 and 2023 September 15. In the full CHIME/FRB sample, only 2.4$\pm 0.4\%$ of sources have been observed to repeat, and we do not find evidence for significant evolution of this value over the duration of the experiment. We find no substantial evidence for bimodal populations of one-off and repeating FRBs in their burst rate distributions; the distribution of upper limits on repeat rates implied from observations of as-yet one-offs is entirely contained within the observed range of repeater burst rates and the distributions do not appear inconsistent. Similarly, using the population analysis framework of C. W. James (2023), we find that our observations of repeating and yet-one-off FRBs are equally well fit assuming a power-law distribution of repeat rates with 50$-$100% of the population repeating.

astro-ph.HE↗

arXiv2026

Radio Monitoring Campaign of Active Repeater FRB 20220912A with CHIME

FRB 20220912A is a highly active repeating fast radio burst (FRB) source, discovered by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) using its real-time FRB detection system (CHIME/FRB). Here, we present results from a radio monitoring campaign of FRB 20220912A using CHIME, including ~200 hours of data collected by CHIME/Pulsar, spanning 1.5 years following the source's discovery. We present an analysis of a sample of 828 CHIME-detected bursts from FRB 20220912A, in the 400-800 MHz radio frequency band. The source remains highly active for ~10 weeks and has a bimodal wait-time distribution with peaks at $160^{+120}_{-70}$ ms and $306^{+14}_{-13}$ s. Assuming a radio efficiency factor of $10^{-4}$ and a beaming angle of 0.1, we estimate the total emitted energy from the source over the entire observing campaign to be $2 \times 10^{43}$ ergs. We report a 2.3$σ$ detection of a linear increase in the DM of $1.4 \pm 0.6$ pc cm$^{-3}$ yr$^{-1}$, with no significant trend in rotation measure (with a 3$σ$ upper limit of 13.4 rad m$^{-2}$ yr$^{-1}$). We contrast our findings with other active repeaters, which exhibit different DM and RM evolution to indicate that FRB 20220912A may reside in a unique local environment.

astro-ph.HE↗

arXiv2026

A steadily declining dispersion measure for the repeating fast radio burst FRB 20220529A: Evidence for an FRB engine embedded in an expanding supernova remnant

We present the discovery and subsequent 3.2 year monitoring campaign of the repeating fast radio burst FRB 20220529A with CHIME/FRB. We observe a gradual dispersion measure (DM) decline of $-0.881\pm0.001~\mathrm{pc}~\mathrm{cm}^{-3}~\mathrm{year}^{-1}$ ($-1.235\pm0.001~\mathrm{pc}~\mathrm{cm}^{-3}~\mathrm{year}^{-1}$ in the rest frame), implying a $\geq3.5\pm0.2$% decrease of the total electron column in the source environment, and we see scattering timescale variations over weeks to years. We observe a short-lived excursion in which the DM rises by $\sim 1~\mathrm{pc}~\mathrm{cm}^{-3}$, immediately preceding a transient $\sim 2000~\mathrm{rad}~\mathrm{m}^{-2}$ Faraday rotation measure (RM) increase previously reported for this source, before returning to its gradual DM decline. We identify a local line-of-sight magnetic field around FRB 20220529A during this DM/RM excursion of $3.4 \pm 0.2~\mathrm{mG}$, corresponding to one of the most strongly magnetized FRB environments. We measure a decrease in the linear polarization fraction of FRB 20220529A bursts with decreasing frequency that we attribute to depolarization from multi-path propagation in the source environment. We also place a $5σ$ upper limit on the spectral luminosity of an associated persistent radio source of $\leq 5\times10^{28}~\mathrm{erg}~\mathrm{s}^{-1}~\mathrm{Hz}^{-1}$ at 1.5 GHz. These observations are consistent with FRB 20220529A originating from a young ($\sim$ years to centuries old) expanding supernova remnant, with short-lived DM and RM variability arising from interactions with the supernova remnant or with a binary companion.

astro-ph.HE↗

arXiv2026

Constraining the mass of the M31 ionized baryon Halo using CHIME/FRB Catalog 2

The circumgalactic medium (CGM) surrounding galaxies is believed to be a significant reservoir of baryons, yet its total mass remains poorly constrained. We present a novel approach to probe the CGM of the Andromeda galaxy (M31) using fast radio bursts (FRBs) from the CHIME/FRB Catalog 2. By comparing the dispersion measures (DMs) of 171 FRBs whose sightlines intersect M31's halo (within $r_{\rm vir}= 302\,\mathrm{kpc}$) to a control sample of 684 FRBs, we estimate the DM contribution from M31's CGM. We find evidence for an excess DM of $δ\mathrm{DM} = 5.9$--$59.6\,\mathrm{pc\,cm^{-3}}$ in the inner halo ($\approx 0$--$151\,\mathrm{kpc}$) and $δ\mathrm{DM} = 25.7$--$64.6\,\mathrm{pc\,cm^{-3}}$ in the outer halo ($\approx 151$--$302\,\mathrm{kpc}$). Using a generalized halo model parameterized by a closure radius $r_{\mathrm{close}}$, we constrain the baryon distribution and infer a best-fit value for $r_{\mathrm{close}}$ to be $9.2^{+9.9}_{-4.9}\,r_{\rm vir}$ ($1σ$), corresponding to a total CGM mass of $M_{b,\mathrm{halo}} = 18.6^{+7.9}_{-8.4} \times 10^{10}\,M_\odot$. Our results suggest that M31 may harbor a substantial fraction of its cosmic baryon budget in diffuse, ionized gas. This work demonstrates the potential of FRBs as a powerful tool for studying the CGM of nearby galaxies, with future larger samples expected to provide tighter constraints on the baryon content of galactic halos.

astro-ph.GA↗

arXiv2026

Probing the maximum energy of fast radio bursts using thousands of sources from the Second CHIME/FRB Catalog

Quantifying the maximum energy of fast radio bursts (FRBs) can provide stringent constraints on their emission mechanisms and progenitor models. However, the most energetic bursts are rare, requiring a large sample of FRBs to detect them. In this work, we use the largest available such sample, 2,998 one-off FRBs from the Second CHIME/FRB Catalog, to obtain a lower limit on the maximum energy ($E^{\mathrm{max}}_{\mathrm{iso}}$) of FRBs, assuming isotropic energy distribution from FRB sources. In the absence of known redshifts ($z$) for most sources, we present a framework that uses the dispersion measures (DMs) and fluences of these FRBs, together with the probability distribution of $z$ given DM, to derive the lower limit on $E^{\mathrm{max}}_{\mathrm{iso}}$. We generate simulated FRB samples assuming different parameter values for a log-normal $\mathrm{DM}_{\mathrm{host}}$ distribution and a Schechter function form of the FRB energy function to estimate how many outliers -- FRBs with large DM contributions from the host galaxy or intervening galaxy halos -- could artificially inflate this limit. After accounting for outliers, the lower limit on $E^{\mathrm{max}}_{\mathrm{iso}}$ from Catalog 2 FRBs ranges between $1.2\times10^{41}$ and $1.9\times10^{42}$ erg, with best estimate $1.2\times10^{42}$ erg. This limit is consistent with those derived from much smaller FRB samples. Moreover, inferred energies of hundreds of FRBs appear collectively limited around $\sim10^{42}$ erg, suggesting a physical limit on the energy reservoir of FRB sources. The corresponding isotropic-equivalent FRB source energy is consistent with the total energy available in a magnetar's external dipole magnetic field, supporting magnetars as FRB progenitors.

astro-ph.HE↗

arXiv2026

The Second CHIME/FRB Catalog of Fast Radio Bursts

We present a catalog of 4539 fast radio bursts (FRBs) observed with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope between 25 July 2018 and 15 September 2023. These bursts originate from 3641 unique sources, including 981 bursts from 83 known repeating sources. For each FRB, the catalog provides a $O(10')$ estimate of sky location along with corresponding measurements of cumulative exposure time and survey sensitivity over the observing period. It includes a total-intensity dynamic spectrum between 400 and 800 MHz at 0.983 ms resolution. From this spectrum, we constrain a model of the burst morphology and measure key parameters such as arrival time, intrinsic temporal width, dispersion measure, scattering time, and flux density. This second catalog includes all FRBs from the first catalog, with every event reprocessed using a uniform and improved analysis framework. We show that previously published inferences remain valid under the updated measurements. We assess consistency of the detection rate across observational parameters, present initial distributions of burst properties, and outline ongoing and future studies that will use this catalog to investigate the nature of FRBs and their utility as astrophysical and cosmological probes.

astro-ph.HE↗

arXiv2025

CHIME/FRB/Pulsar discovery of a nearby long period radio transient with a timing glitch

We present the discovery of a 421 s long period radio transient (LPT) using the CHIME telescope, CHIME J0630+25. The source is localized to RA=06:30:38.4$\pm1'$ Dec=25:26:24$\pm1'$ using voltage data acquired with the CHIME baseband system. A timing analysis shows that a model including a glitch is preferred over a non-glitch model with $dF/F=1.3\times10^{-6}$, consistent with other glitching neutron stars. The timing model suggests a surface magnetic field of $\sim1.5\times10^{15}$ G and a characteristic age of $\sim1.28\times10^{6}$ yrs. A separate line of evidence to support a strong local magnetic field is an abnormally high rotation measure of $RM=-347.8(6) \mathrm{rad\, m^{-2}}$ relative to CHIME J0630+25's modest dispersion measure of 22(1) pc cm$^{-2}$, implying a dense local magneto-ionic structure. As a result, we believe that CHIME J0630+25 is a magnetized, slowly spinning, isolated neutron star. This marks CHIME J0630+25 as the longest period neutron star and the second long period neutron star with an inferred magnetar-like field. Based on dispersion measure models and comparison with pulsars with distance measurements, CHIME J0630+25 is located at a nearby distance of 170$^{+310}_{-100}$ pc (95.4\%), making it an ideal candidate for follow-up studies.

astro-ph.HE↗

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↗

arXiv2025

Constraining the Faint-End Slope of the FRB Energy Function Using CHIME/FRB Catalog-1 and Local Volume Galaxies

Despite hundreds of detected fast radio bursts (FRBs), the faint-end slope ($γ$) of their energy distribution remains poorly constrained, hindering understanding of whether bright, cosmological FRBs and faint, Galactic magnetar SGR 1935+2154-like bursts share a common origin. In this study, we constrain this faint-end slope, modeled with a Schechter-like distribution, by searching for potential associations between bursts from the CHIME/FRB Catalog-1 and galaxies in the local volume. We cross-matched Catalog-1 FRBs with 495 local volume galaxies within 21 Mpc, identified from the HECATE catalog, and found no associations. Assuming the FRB energy function extends to $\sim 3 \times 10^{34}$ erg-the energy of the Galactic magnetar burst from SGR 1935+2154-this null result constrains $γ$ to be $<$ 2.3 (95% confidence upper limit), representing the first empirical estimate for extragalactic FRBs at such low energies. This finding supports the hypothesis that the FRB population is dominated by bright, likely cosmological bursts with a relatively flat energy distribution ($γ< 2.5$). However, the constraint weakens if higher energy thresholds are assumed. A flatter energy function is consistent with the observed anti-correlation between FRB dispersion measure and fluence, as seen across various observational bands. While the contribution of low-energy bursts, such as those from the Galactic magnetar SGR 1935+2154, appears minimal, our results suggest that normal magnetars like SGR 1935+2154 could dominate the FRB population if their burst rates and energies scale with age and magnetic field. Upcoming CHIME/FRB Catalog-2 data and targeted nearby galaxy surveys will further refine these constraints, offering critical insight into whether FRBs arise from a single population or diverse origins.

astro-ph.HE↗

arXiv2025

FRB 20250316A: A Brilliant and Nearby One-Off Fast Radio Burst Localized to 13 parsec Precision

Precise localizations of a small number of repeating fast radio bursts (FRBs) using very long baseline interferometry (VLBI) have enabled multiwavelength follow-up observations revealing diverse local environments. However, the 2--3\% of FRB sources that are observed to repeat may not be representative of the full population. Here we use the VLBI capabilities of the full CHIME Outriggers array for the first time to localize a nearby (40 Mpc), bright (kJy), and apparently one-off FRB source, FRB 20250316A, to its environment on 13-pc scales. We use optical and radio observations to place deep constraints on associated transient emission and the properties of its local environment. We place a $5σ$ upper limit of $L_{\mathrm{9.9~\mathrm{GHz}}} < 2.1\times10^{25}~\mathrm{erg~s^{-1}~Hz^{-1}}$ on spatially coincident radio emission, a factor of 100 lower than any known compact persistent radio source associated with an FRB. Our KCWI observations allow us to characterize the gas density, metallicity, nature of gas ionization, dust extinction and star-formation rate through emission line fluxes. We leverage the exceptional brightness and proximity of this source to place deep constraints on the repetition of FRB 20250316A, and find it is inconsistent with all well-studied repeaters given the non-detection of bursts at lower spectral energies. We explore the implications of a measured offset of 190$\pm20$ pc from the center of the nearest star-formation region, in the context of progenitor channels. FRB 20250316A marks the beginning of an era of routine localizations for one-off FRBs on tens of mas-scales, enabling large-scale studies of their local environments.

astro-ph.HE↗

arXiv2025

James Webb Space Telescope Observations of the Nearby and Precisely-Localized FRB 20250316A: A Potential Near-IR Counterpart and Implications for the Progenitors of Fast Radio Bursts

We present deep James Webb Space Telescope near-infrared imaging to search for a quiescent or transient counterpart to FRB 20250316A, which was precisely localized with the CHIME/FRB Outriggers array to an area of $11\times13$ pc in the outer regions of NGC 4141 at $d\approx40$ Mpc. Our F150W2 image reveals a faint source near the center of the FRB localization region ("NIR-1"; $M_{\rm F150W2}\approx-2.5$ mag; probability of chance coincidence $\approx0.36$), the only source within $\approx2.7σ$. We find that it is too faint to be a globular cluster, young star cluster, red supergiant star, or a giant star near the tip of the red giant branch (RGB). It is instead consistent with a red giant near the RGB "clump" or a massive ($\gtrsim20$ M$_{\odot}$) main sequence star, although the latter explanation is less likely. The source is too bright to be a supernova remnant, Crab-like pulsar wind nebula, or isolated magnetar. Alternatively, NIR-1 may represent transient emission, namely a dust echo from an energetic outburst associated with the FRB, in which case we would expect it to fade in future observations. We explore the stellar population near the FRB and find that it is composed of a mix of young massive stars ($\sim10-100$ Myr) in a nearby HII region that extends to the location of FRB 20250316A, and old evolved stars ($\gtrsim$ Gyr). The overlap with a young stellar population, containing stars of up to $\approx20$ M$_\odot$, may implicate a neutron star / magnetar produced in the core collapse of a massive star as the source of FRB 20250316A.

astro-ph.HE↗

arXiv2025

Measurement of the Dispersion$\unicode{x2013}$Galaxy Cross-Power Spectrum with the Second CHIME/FRB Catalog

The dispersion of extragalactic fast radio bursts (FRBs) can serve as a powerful probe of the diffuse plasma between and surrounding galaxies, which contains most of the Universe's baryons. By cross-correlating the dispersion of background FRBs with the locations of foreground galaxies, we can study the relative spatial distributions of plasma and galaxies on scales of 0.1 to 50 Mpc, which are strongly affected by feedback processes in galaxy formation. Here we present the measurement of the dispersion$\unicode{x2013}$galaxy angular cross-power spectrum between 2873 FRBs from the Second CHIME/FRB Catalog and nearly 6 million galaxies from the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Survey. Over five photometric galaxy redshift bins spanning $0.05 < z <0.5$ and at 5.1$σ$ significance, we make the first definitive detection of spatial correlations in FRB dispersion measure due to cosmic structure. While parameter inferences should be interpreted with caution because of incomplete modelling of both the signal and systematic errors, our data indicate that the plasma$\unicode{x2013}$galaxy cross-power spectrum cuts off relative to the matter power spectrum at a scale $k_\textrm{cut}^{-1}=0.9^{+0.4}_{-0.4}\,\textrm{Mpc}$. This scale is consistent with those X-ray stacking analyses that suggest dark-matter halos with group-scale masses are largely evacuated of their baryons by feedback processes. Our study demonstrates that FRBs are promising tools to discern the physics of baryonic structure formation and will only become more powerful as FRB surveys expand.

astro-ph.CO↗