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1. Fast radio bursts at the dawn of the 2020s

   https://doi.org/10.1007/s00159-022-00139-w  

   Petroff, E. ; Hessels, J. W. T. ; Lorimer, D. R. ( March 2022 , The Astronomy and Astrophysics Review)

   Since the discovery of the first fast radio burst (FRB) in 2007, and their confirmation as an abundant extragalactic population in 2013, the study of these sources has expanded at an incredible rate. In our 2019 review on the subject, we presented a growing, but still mysterious, population of FRBs—60 unique sources, 2 repeating FRBs, and only 1 identified host galaxy. However, in only a few short years, new observations and discoveries have given us a wealth of information about these sources. The total FRB population now stands at over 600 published sources, 24 repeaters, and 19 host galaxies. Higher time resolution data, sustained monitoring, and precision localisations have given us insight into repeaters, host galaxies, burst morphology, source activity, progenitor models, and the use of FRBs as cosmological probes. The recent detection of a bright FRB-like burst from the Galactic magnetar SGR 1935 + 2154 provides an important link between FRBs and magnetars. There also continue to be surprising discoveries, like periodic modulation of activity from repeaters and the localisation of one FRB source to a relatively nearby globular cluster associated with the M81 galaxy. In this review, we summarise the exciting observational results from the past few years. We also highlight their impact on our understanding of the FRB population and proposed progenitor models. We build on the introduction to FRBs in our earlier review, update our readers on recent results, and discuss interesting avenues for exploration as the field enters a new regime where hundreds to thousands of new FRBs will be discovered and reported each year.

    

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2. Inferring the Energy and Distance Distributions of Fast Radio Bursts Using the First CHIME/FRB Catalog

   https://doi.org/10.3847/1538-4357/acaf06  

   Shin, Kaitlyn ; Masui, Kiyoshi W. ; Bhardwaj, Mohit ; Cassanelli, Tomas ; Chawla, Pragya ; Dobbs, Matt ; Dong, Fengqiu Adam ; Fonseca, Emmanuel ; Gaensler, B. M. ; Herrera-Martín, Antonio ; et al ( February 2023 , The Astrophysical Journal)

   Fast radio bursts (FRBs) are brief, energetic, typically extragalactic flashes of radio emission whose progenitors are largely unknown. Although studying the FRB population is essential for understanding how these astrophysical phenomena occur, such studies have been difficult to conduct without large numbers of FRBs and characterizable observational biases. Using the recently released catalog of 536 FRBs published by the Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst (CHIME/FRB) collaboration, we present a study of the FRB population that also calibrates for selection effects. Assuming a Schechter function, we infer a characteristic energy cut-off of$E_{\mathrm{char}}={2.38}_{-1.64}^{+5.35}\times {10}^{41}$erg and a differential power-law index ofγ=$-{1.3}_{-0.4}^{+0.7}$. Simultaneously, we infer a volumetric rate of [${7.3}_{-3.8}^{+8.8}$(stat.)${}_{-1.8}^{+2.0}(\mathrm{sys}.)]\times {10}^4$Gpc⁻³yr⁻¹above a pivot energy of 10³⁹erg and below a scattering timescale of 10 ms at 600 MHz, and find we cannot significantly constrain the cosmic evolution of the FRB population with star-formation rate. Modeling the host’s dispersion measure (DM) contribution as a log-normal distribution and assuming a total Galactic contribution of 80 pc cm⁻³, we find a median value of${\mathrm{DM}}_{\mathrm{host}}={84}_{-49}^{+69}$pc cm⁻³, comparable with values typically used in the literature. Proposed models for FRB progenitors should be consistent with the energetics and abundances of the full FRB population predicted by our results. Finally, we infer the redshift distribution of FRBs detected with CHIME, which will be tested with the localizations and redshifts enabled by the upcoming CHIME/FRB Outriggers project.

    

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3. Scattering variability detected from the circumsource medium of FRB 20190520B

   https://doi.org/10.1093/mnras/stac3547  

   Ocker, Stella Koch ; Cordes, James M. ; Chatterjee, Shami ; Li, Di ; Niu, Chen-Hui ; McKee, James W. ; Law, Casey J. ; Anna-Thomas, Reshma ( December 2022 , Monthly Notices of the Royal Astronomical Society)

   Fast radio bursts (FRBs) are millisecond-time-scale radio transients, the origins of which are predominantly extragalactic and likely involve highly magnetized compact objects. FRBs undergo multipath propagation, or scattering, from electron density fluctuations on sub-parsec scales in ionized gas along the line of sight. Scattering observations have located plasma structures within FRB host galaxies, probed Galactic and extragalactic turbulence, and constrained FRB redshifts. Scattering also inhibits FRB detection and biases the observed FRB population. We report the detection of scattering times from the repeating FRB 20190520B that vary by up to a factor of 2 or more on minutes to days-long time-scales. In one notable case, the scattering time varied from 7.9 ± 0.4 ms to less than 3.1 ms ($95{{\ \rm per\ cent}}$ confidence) over 2.9 min at 1.45 GHz. The scattering times appear to be uncorrelated between bursts or with dispersion and rotation measure variations. Scattering variations are attributable to dynamic, inhomogeneous plasma in the circumsource medium, and analogous variations have been observed from the Crab pulsar. Under such circumstances, the frequency dependence of scattering can deviate from the typical power law used to measure scattering. Similar variations may therefore be detectable from other FRBs, even those with inconspicuous scattering, providing a unique probe of small-scale processes within FRB environments.

    

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4. Radio Scattering Horizons for Galactic and Extragalactic Transients

   https://doi.org/10.3847/1538-4357/ac75ba  

   Ocker, Stella Koch ; Cordes, James M. ; Chatterjee, Shami ; Gorsuch, Miranda R. ( July 2022 , The Astrophysical Journal)

   Radio wave scattering can cause severe reductions in detection sensitivity for surveys of Galactic and extragalactic fast (∼ms duration) transients. While Galactic sources like pulsars undergo scattering in the Milky Way interstellar medium (ISM), extragalactic fast radio bursts (FRBs) can also experience scattering in their host galaxies and other galaxies intervening in their lines of sight. We assess Galactic and extragalactic scattering horizons for fast radio transients using a combination of NE2001 to model the dispersion measure and scattering time (τ) contributed by the Galactic disk, and independently constructed electron density models for the Galactic halo and other galaxies’ ISMs and halos that account for different galaxy morphologies, masses, densities, and strengths of turbulence. For source redshifts 0.5 ≤z_s≤ 1, an all-sky, isotropic FRB population has simulated values ofτ(1 GHz) ranging from ∼1μs to ∼2 ms (90% confidence, observer frame) that are dominated by host galaxies, althoughτcan be ≫2 ms at low Galactic latitudes. A population atz_s= 5 has 0.01 ≲τ≲ 300 ms at 1 GHz (90% confidence), dominated by intervening galaxies. About 20% of these high-redshift FRBs are predicted to haveτ> 5 ms at 1 GHz (observer frame), and ≳40% of FRBs betweenz_s∼ 0.5–5 haveτ≳ 1 ms forν≤ 800 MHz. Our scattering predictions may be conservative if scattering from circumsource environments is significant, which is possible under specific conditions. The percentage of FRBs selected against from scattering could also be substantially larger than we predict if circumgalactic turbulence causes more small-scale (≪1 au) density fluctuations than observed from nearby halos.

    

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5. Proposed Host Galaxies of Repeating Fast Radio Burst Sources Detected by CHIME/FRB

   https://doi.org/10.3847/1538-4357/ad0893  

   Ibik, Adaeze L. ; Drout, Maria R. ; Gaensler, B. M. ; Scholz, Paul ; Michilli, Daniele ; Bhardwaj, Mohit ; Kaspi, Victoria M. ; Pleunis, Ziggy ; Cassanelli, Tomas ; Cook, Amanda M. ; et al ( January 2024 , The Astrophysical Journal)

   We present a search for host galaxy associations for the third set of repeating fast radio burst (FRB) sources discovered by the CHIME/FRB Collaboration. Using the ∼1′ CHIME/FRB baseband localizations and probabilistic methods, we identify potential host galaxies of two FRBs, 20200223B and 20190110C at redshifts of 0.06024(2) and 0.12244(6), respectively. We also discuss the properties of a third marginal candidate host galaxy association for FRB 20191106C with a host redshift of 0.10775(1). The three putative host galaxies are all relatively massive, fall on the standard mass–metallicity relationship for nearby galaxies, and show evidence of ongoing star formation. They also all show signatures of being in a transitional regime, falling in thegreen valley, which is between the bulk of star-forming and quiescent galaxies. The plausible host galaxies identified by our analysis are consistent with the overall population of repeating and nonrepeating FRB hosts while increasing the fraction of massive and bright galaxies. Coupled with these previous host associations, we identify a possible excess of FRB repeaters whose host galaxies haveM_u−M_rcolors redder than the bulk of star-forming galaxies. Additional precise localizations are required to confirm this trend.

    

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