Adam Lanman

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, 2998 one-off FRBs from the Second CHIME/FRB Catalog, to obtain a lower limit on the maximum energy ( E iso max ) 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 iso max . We generate simulated FRB samples assuming different parameter values for a log-normal DM _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 iso max from Catalog 2 FRBs ranges between 1.1 × 10 ⁴¹ and 1.9 × 10 ⁴² erg, with best estimate 1.5 × 10 ⁴² erg. This limit is consistent with estimates of the Schechter function cutoff energy ( E iso cutoff ) derived from much smaller FRB samples. Moreover, inferred energies of hundreds of FRBs appear collectively limited around ∼10 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.

In recent years, localized fast radio bursts (FRBs) have emerged as a powerful tool to study the structure of the baryonic matter in the Universe. Their dispersion measures (DMs) scale linearly with electron density independent of gas temperature, making them particularly well suited to studying the intragroup medium (IGrM), where traditional probes such as X-ray emission and the Sunyaev–Zeldovich effect are weak. Evidence suggests that the gas in group mass halos ( M ₅₀₀ ∼ 10 ¹³ –10 ¹⁴ M _⊙ ) is strongly affected by galactic feedback, causing deviations from cluster scaling relations. Three FRBs from the first CHIME/FRB Outrigger sample come from host galaxies found within or behind galaxy clusters and groups. We estimate the DM contribution of each ICM/IGrM by integrating different halo density profiles, accounting for uncertainties in halo mass and the host galaxy line-of-sight distance. For the more massive halos, predicted cluster DMs agree with the extragalactic DM budget. One burst, FRB 20230703A, intersects three groups yet has a low extragalactic DM. By comparing model predictions with the measured DM, we constrain the gas mass fraction f _g ( R ) in these halos. Comparing with published M – f _g relations, we find consistency with recent eROSITA results at R ₅₀₀ and mild tension at R ₂₀₀ and with earlier X-ray–based relations. As CHIME/FRB Outriggers build a large catalog of localized FRBs, many additional sightlines through groups and clusters will be obtained. These will enable systematic tests of intragroup and intracluster gas properties and sharpen constraints on the distribution of baryons in massive halos.

We present a catalog of 4539 fast radio bursts (FRBs) observed with the Canadian Hydrogen Intensity Mapping Experiment telescope between 2018 July 25 and 2023 September 15. These bursts originate from 3641 unique sources, including 981 bursts from 83 known repeating sources. For each FRB, the catalog provides an O ( 1 0 ′ ) 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.

We report the first upper limits on the power spectrum of 21 cm fluctuations during the Epoch of Reionization and Cosmic Dawn from Phase II of the Hydrogen Epoch of Reionization Array (HERA) experiment. HERA Phase II constitutes several significant improvements in the signal chain compared to Phase I, most notably resulting in expanded frequency bandwidth, from 50–250 MHz. In these first upper limits, we investigate a small two-week subset of the available Phase II observations, with a focus on identifying new systematic characteristics of the instrument, and establishing an analysis pipeline to account for them. We report 2 σ upper limits in eight spectral bands, spanning 5.6 ≤ z ≤ 24.4 that are consistent with thermal noise at the 2 σ level for k ≳ 0.6–0.9 h Mpc ⁻¹ (band dependent). Our tightest limit during Cosmic Dawn ( z > 12) is 1.13 × 10 ⁶ mK ² at ( k = 0.55 h Mpc ⁻¹ , z = 16.78), and during the EoR (5.5 < z < 12), it is 1.78 × 10 ³ mK ² at ( k = 0.70 h Mpc ⁻¹ , z = 7.05). We find that mutual coupling has become our dominant systematic, leaking foreground power that strongly contaminates the low- k modes, resulting in the loss of modes from k = 0.35 to 0.55 compared to Phase I data.

Among the thousands of observed fast radio bursts (FRBs), a few sources exhibit exceptionally high burst activity observable by many telescopes across a broad range of radio frequencies. Almost all of these highly active repeaters have been discovered by the Canadian Hydrogen Intensity Mapping Experiment/FRB project (CHIME/FRB), due to its daily observations of the entire northern sky as a transit radio telescope. FRB 20240114A is a source discovered and reported by CHIME/FRB to the community in 2024 January; given its low declination, even the detection of a few bursts hints at a high burst rate. Following the community announcement of this source as a potentially active repeater, it was extensively followed up by other observatories and has emerged as one of the most prolific FRB repeaters ever observed. This paper presents the five bursts CHIME/FRB observed from FRB 20240114A, with channelized raw voltage data saved for two bursts. We do not observe changes in the dispersion measure of the source greater than ∼1.3 pc cm ⁻³ in our observations over a nearly 1 yr baseline. We find a rotation measure of ∼+320 rad m ⁻² . We do not find evidence for scattering at the level of <0.3 ms in the bursts, and we find no evidence for astrophysical scintillation. In our observations of FRB 20240114A, we see a burst rate ∼49 times higher than the median upper limit on the burst rate of apparent nonrepeaters also discovered by CHIME/FRB. With many thousands of bursts observed to date, FRB 20240114A has given the field an extraordinary opportunity to extensively study an FRB and understand its origins.

We analyze the positional and morphological properties of about 3600 unique fast radio burst (FRB) sources reported in the second FRB catalog generated by the Canadian Hydrogen Intensity Mapping Experiment (CHIME) telescope. We find a two-dimensional dependence of FRB detections on sky position and identify a significant absence of detections in a roughly circular region centered at Galactic coordinates (77 . ° 7, 0 . ° 9), spanning an area of 213.6 deg ² . This detection gap spatially coincides with the Cygnus X region—a plasma-rich star-forming region in the Milky Way. This feature is most likely the result of increased sky temperature and strong multipath scattering by turbulent ionized plasma, which broadens the FRB signals beyond detectability in the CHIME band. Our simulations yield a mean of six expected FRB detections within the gap when accounting for the elevated sky temperature in the direction of the detection gap. We infer that a lower limit of the maximum scattering timescale τ _{sc, 1 GHz} ≥ 5.59 ms, obtained without assuming a model of the Galactic electron distribution, is sufficient to suppress the brightness of all coincident FRBs. A similar suppression is seen in Catalog 2 along other high emission measure (EM) sight lines (i.e., EM ≥ 2900 pc cm ⁻⁶ ), further supporting a broader trend of suppression due to Galactic scattering. Future very long baseline interferometry measurements of scattering disks with CHIME Outriggers can help confirm our interpretation. Our work highlights the notion that FRBs can serve as new, model-independent tracers of the warm ionized medium within our Galaxy.

Fast radio bursts (FRBs) are unique probes of extragalactic ionized baryonic structure as each signal, through its burst properties, holds information about the ionized matter it encounters along its sightline. FRB 20200723B is a burst with a scattering timescale of τ _{400 MHz} > 1 s at 400 MHz and a dispersion measure of DM ∼244 pc cm ⁻³ . Observed across the entire Canadian Hydrogen Intensity Mapping Experiment (CHIME)/FRB frequency band, it is the single-component burst with the largest scattering timescale yet observed by CHIME/FRB. The combination of its high scattering timescale and relatively low dispersion measure present an uncommon opportunity to use FRB 20200723B to explore the properties of the cosmic web it traversed. With an ∼arcminute-scale localization region, we find the most likely host galaxy is NGC 4602 (with PATH probability P ( O ∣ x ) = 0.985), which resides ∼30 Mpc away within a cosmic sheet structure on the outskirts of the Virgo Cluster. We place an upper limit on the average free electron density of this cosmic structure of 〈 n e 〉 < 4 . 6 − 2.0 + 9.6 × 1 0 − 5 cm ⁻³ , broadly consistent with expectations from cosmological simulations. We investigate whether the source of scattering lies within the same galaxy as the FRB, or at a farther distance from an intervening structure along the line of sight. Comparing with Milky Way pulsar observations, we suggest the scattering may originate from within the host galaxy of FRB 20200723B.