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The Large Dispersion and Scattering of FRB 20190520B Are Dominated by the Host Galaxy
Ist Teil von
The Astrophysical journal, 2022-06, Vol.931 (2), p.87
Ort / Verlag
Philadelphia: The American Astronomical Society
Erscheinungsjahr
2022
Quelle
EZB Electronic Journals Library
Beschreibungen/Notizen
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 Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delay
τ
(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δ
ν
d
(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an H
α
emission measure (galaxy frame) EM
s
= 620 pc cm
−6
× (
T
/10
4
K)
0.9
, implying DM
H
α
of order the value inferred from the FRB DM budget,
DM
h
=
1121
−
138
+
89
pc cm
−3
for plasma temperatures greater than the typical value 10
4
K. Combining
τ
and DM
h
yields a nominal constraint on the scattering amplification from the host galaxy
F
˜
G
=
1.5
−
0.3
+
0.8
(
pc
2
km
)
−
1
/
3
, where
F
˜
describes turbulent density fluctuations and
G
represents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry where
τ
arises from the host galaxy and Δ
ν
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 the
τ
–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.