The Second CHIME/FRB Catalog of Fast Radio Bursts

TL;DR

This work updates CHIME/FRB catalogs with Catalog 2, containing 4539 FRBs from 3641 sources observed from 2018 to 2023, all reprocessed with a uniform analysis framework. It delivers per-event measurements including sky localization with exposure-weighted estimates, total-intensity dynamic spectra in 400–800 MHz at 0.983 ms resolution, and fitburst-based morphology, dispersion measure, scattering, flux density, and fluence, plus associated sensitivity thresholds. Validation shows population-level inferences from Catalog 1 remain valid under the new analysis, while exposing instrumental biases and residual rate variations that are addressed with exposure and sensitivity corrections. The catalog serves as a basis for FRB progenitor and cosmology studies and enables future work such as injection campaigns, baseband analyses, repeater discovery, cross-correlations with galaxies, and real-time low-frequency VLBI via outriggers.

Abstract

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.

Figures (15)

• Figure 1: Sky distributions of 3558 non-repeating sources and 83 repeating sources (Cook et al., in preparation) are shown as blue circles and red stars, respectively. Marker color indicates the extragalactic $\text{DM}$, obtained by subtracting the Galactic DM -- estimated using the NE2001 model ne2001 and a 30 pc cm$^{-3}$ contribution from the Galactic halo cbg+23 -- from the measured DM. For repeating sources, we show the inverse-variance-weighted average of the localizations and extragalactic DM values from all associated bursts (see §\ref{['sec:repeater']} for details on the methodology used to identify repeating FRBs). The gray shaded region at the bottom indicates declinations outside the CHIME/FRB field of view ($\text{decl.}\xspace \leq -9.5^{\circ}$). The black line marks the Galactic plane, while thin gray lines denote graticules of constant Galactic longitude, spaced by $30^{\circ}$. As a transit telescope, CHIME provides relatively uniform exposure in this Mercator projection of equatorial coordinates.
• Figure 2: Daily sensitivity variation from 4 September 2018 to 15 September 2023. The vertical axis represents the relative RMS noise, $\sigma_{\rm pulsar}(t)$, computed from the $\text{S/N}$ of individual pulses detected from a selection of known pulsars transiting overhead aab+21. The color bar indicates the number of distinct pulsars detected per day. Dashed gray lines mark days where the RMS noise variation exceeded 10%; these days, comprising approximately 4.5% of the total observing time, were excluded from the final exposure calculation. Reduced sensitivity observed during early 2023 corresponds to heavy snowfall at the site in January and February of that year.
• Figure 3: Galactic coordinate sky maps, depicting the locations of all non-repeating (blue circles) and repeating (red crosses) FRB sources observed during the period from 4 September 2018 to 15 September 2023, overlaid on the total exposure of the CHIME/FRB system during that time. The top panel displays the sky locations that transit through the primary beam of the telescope once per day (with $\text{decl.}\xspace < 70^{\circ}$), while the bottom panels illustrate the upper (left) and lower (right) transit exposures for sources that transit through the primary beam twice per day (with $\text{decl.}\xspace > 70^{\circ}$). The bottom panel maps are centered on the North Celestial Pole and utilize a logarithmic color scale. We detect fewer FRBs in the lower transit due to reduced sensitivity.
• Figure 4: Total exposure per source in Catalog 2 shown for the observational period from 4 September 2018 to 15 September 2023. The left panel displays the exposure during upper and lower transits as a function of both declination and zenith angle. FRBs with $\text{decl.}\xspace > 70^{\circ}$ undergo two transits through CHIME's field of view, with the transits exhibiting different durations and consequently different exposure times and sensitivities. The right panel presents the distribution of exposure for sources observed during both upper and lower transits. The error bars account for uncertainties in source localization, as discussed in §\ref{['sec:localization']}.
• Figure 5: (Left.) A scatter plot of revised fitburst estimates of scattering timescale (all referenced to 400.195 MHz) made for FRBs first presented in Catalog 1; a Kolmogorov-Smirnov (KS) test between these two distributions yields a $p$-value of 0.7, indicating that the Catalog 1 and Catalog 2 estimates are statistically consistent despite changes to the fitburst model described in §\ref{['sec:fitburst']}. (Middle.) A similar scatter plot and KS test for fitburst estimates of the spectral running between Catalog 1 and Catalog 2. The statistically significant differences reflect changes in the fitburst model that lead to improved fits against narrow-band (i.e., repeater-like) features in dynamic spectra, which tend to yield large magnitudes of spectral running. (Right.) A similar scatter plot and KS test for the full-width-at-tenth-maximum (FWTM) emission bandwidth, derived from best-fit fitburst models using an algorithm described by p++21.