The repeating fast radio burst FRB 20190520B is an anomaly of the FRB population thanks to its high dispersion measure (DM = 1205 pc cm^{−3}) despite its low redshift of
The FLIMFLAM survey is collecting spectroscopic data of field galaxies near fast radio burst (FRB) sight lines to constrain key parameters describing the distribution of matter in the Universe. In this work, we leverage the survey data to determine the source of the excess extragalactic dispersion measure (DM), compared to Macquart relation estimates of four FRBs: FRB20190714A, FRB20200906A, FRB20200430A, and FRB20210117A. By modeling the gas distribution around the foreground galaxy halos and galaxy groups of the sight lines, we estimate DM_{halos}, their contribution to the FRB DMs. The FRB20190714A sight line shows a clear excess of foreground halos which contribute roughly twothirds of the observed excess DM, thus implying a sight line that is baryon dense. FRB20200906A shows a smaller but nonnegligible foreground halo contribution, and further analysis of the intergalactic medium is necessary to ascertain the true cosmic contribution to its DM. FRB20200430A and FRB20210117A show negligible foreground contributions, implying a large host galaxy excess and/or progenitor environment excess.
more » « less NSFPAR ID:
 10445370
 Publisher / Repository:
 DOI PREFIX: 10.3847
 Date Published:
 Journal Name:
 The Astrophysical Journal
 Volume:
 954
 Issue:
 1
 ISSN:
 0004637X
 Format(s):
 Medium: X Size: Article No. 71
 Size(s):
 ["Article No. 71"]
 Sponsoring Org:
 National Science Foundation
More Like this

Abstract z _{frb}= 0.241. This excess has been attributed to a large host contribution of DM_{host}≈ 900 pc cm^{−3}, far larger than any other known FRB. In this paper, we describe spectroscopic observations of the FRB 20190520B field obtained as part of the FLIMFLAM survey, which yielded 701 galaxy redshifts in the field. We find multiple foreground galaxy groups and clusters, for which we then estimated halo masses by comparing their richness with numerical simulations. We discover two separateM _{halo}> 10^{14}M _{⊙}galaxy clusters atz = 0.1867 and 0.2170 that are directly intersected by the FRB sight line within their characteristic halo radiusr _{200}. Subtracting off their estimated DM contributions, as well that of the diffuse intergalactic medium, we estimate a host contribution of or ${\mathrm{D}\mathrm{M}}_{\mathrm{h}\mathrm{o}\mathrm{s}\mathrm{t}}={430}_{220}^{+140}$ (observed frame), depending on whether we assume that the halo gas extends to ${280}_{170}^{+140}\phantom{\rule{0.25em}{0ex}}\mathrm{p}\mathrm{c}\phantom{\rule{0.25em}{0ex}}{\mathrm{c}\mathrm{m}}^{3}$r _{200}or 2 ×r _{200}. This significantly smaller DM_{host}—no longer the largest known value—is now consistent with Hα emission measures of the host galaxy without invoking unusually high gas temperatures. Combined with the observed FRB scattering timescale, we estimate the turbulent fluctuation and geometric amplification factor of the scattering layer to be , suggesting that most of the gas is close to the FRB host. This result illustrates the importance of incorporating foreground data for FRB analyses both for understanding the nature of FRBs and to realize their potential as a cosmological probe. $\tilde{F}G\approx 4.5\u201311{({\mathrm{pc}}^{2}\phantom{\rule{0.25em}{0ex}}\mathrm{km})}^{1/3}$ 
Abstract The distribution of gas in the circumgalactic medium (CGM) of galaxies of all types is poorly constrained. Foreground CGMs contribute an extra amount to the dispersion measure (DM) of fast radio bursts (FRBs). We measure this DM excess for the CGMs of 10^{11}–10^{13}
M _{⊙}halos using the CHIME/FRB first data release, a halo mass range that is challenging to probe in any other way. Because of the uncertainty in the FRBs’ angular coordinates, only for nearby galaxies is the localization sufficient to confidently associate them with intersecting any foreground halo. Thus we stack on galaxies within 80 Mpc, optimizing the stacking scheme to approximately minimize the stack’s variance and marginalize over uncertainties in FRB locations. The sample has 20–30 FRBs intersecting halos with masses of 10^{11}–10^{12}M _{⊙}and also of 10^{12}–10^{13}M _{⊙}, and these intersections allow a marginal 1σ –2σ detection of the DM excess in both mass bins. The bin of 10^{11}–10^{12}M _{⊙}halos also shows a DM excess at 1–2 virial radii. By comparing data with different models for the CGM gas profile, we find that all models are favored by the data up to 2σ level compared to the null hypothesis of no DM excess. With 3000 more bursts from a future CHIME data release, we project a 4σ detection of the CGM. Distinguishing between viable CGM models by stacking FRBs with CHIMElike localization would require tens of thousands of bursts. 
Abstract A sample of 14 FRBs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (IGM), galaxy halos, and the disks of host galaxies. The IGM and galaxy halos contribute significantly to dispersion measures (DMs) but evidently not to scattering, which is then dominated by host galaxies. This enables the usage of scattering times for estimating DM contributions from host galaxies and also for a combined scattering–dispersion redshift estimator. Redshift estimation is calibrated using the scattering of Galactic pulsars after taking into account different scattering geometries for Galactic and intergalactic lines of sight. The DMonly estimator has a bias of ∼0.1 and rms error of ∼0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm^{−3}for the host galaxy’s DM contribution. The combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%–40% smaller rms error. We find that values for the baryonic fraction of the ionized IGM
f _{igm}≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. Our study suggests that 2 of the 14 candidate galaxy associations (FRB 20190523A and FRB 20190611B) should be reconsidered. 
Abstract The repeating fast radio burst FRB 20190520B is localized to a galaxy at
z = 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm^{−3}. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Fivehundredmeter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delayτ (1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δν _{d}(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an Hα emission measure (galaxy frame) EM_{s}= 620 pc cm^{−6}× (T /10^{4}K)^{0.9}, implying DM_{Hα}of order the value inferred from the FRB DM budget, pc cm^{−3}for plasma temperatures greater than the typical value 10^{4}K. Combining ${\mathrm{DM}}_{\mathrm{h}}={1121}_{138}^{+89}$τ and DM_{h}yields a nominal constraint on the scattering amplification from the host galaxy , where $\tilde{F}G\phantom{\rule{0.50em}{0ex}}=\phantom{\rule{0.50em}{0ex}}{1.5}_{0.3}^{+0.8}{({\mathrm{pc}}^{2}\phantom{\rule{0.25em}{0ex}}\mathrm{km})}^{1/3}$ describes turbulent density fluctuations and $\tilde{F}$G represents the geometric leverage to scattering that depends on the location of the scattering material. For a twoscreen scattering geometry whereτ arises from the host galaxy and Δν _{d}from the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using theτ –DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way. 
Abstract The Macquart relation describes the correlation between the dispersion measure (DM) of fast radio bursts (FRBs) and the redshift
z of their host galaxies. The scatter of the Macquart relation is sensitive to the distribution of baryons in the intergalactic medium including those ejected from galactic halos through feedback processes. The variance of the distribution in DMs from the cosmic web (DM_{cosmic}) is parameterized by a fluctuation parameterF . In this work, we present a new measurement ofF using 78 FRBs of which 21 have been localized to host galaxies. Our analysis simultaneously fits for the Hubble constantH _{0}and the DM distribution due to the FRB host galaxy. We find that the fluctuation parameter is degenerate with these parameters, most notablyH _{0}, and use a uniform prior onH _{0}to measure at the 3 ${\mathrm{log}}_{10}F>0.86$σ confidence interval and a new constraint on the Hubble constant . Using a synthetic sample of 100 localized FRBs, the constraint on the fluctuation parameter is improved by a factor of ∼2. Comparing our ${H}_{0}={85.3}_{8.1}^{+9.4}\phantom{\rule{0.25em}{0ex}}\mathrm{km}\phantom{\rule{0.25em}{0ex}}{\mathrm{s}}^{1}\phantom{\rule{0.25em}{0ex}}{\mathrm{Mpc}}^{1}$F measurement to simulated predictions from cosmological simulation (IllustrisTNG), we find agreement between redshifts 0.4 <z andz < 2.0. However, atz < 0.4, the simulations underpredictF , which we attribute to the rapidly changing extragalactic DM excess distribution at low redshift.