Kavli Affiliate: Kiyoshi W. Masui
| First 5 Authors: Swarali Shivraj Patil, Swarali Shivraj Patil, , ,
| Summary:
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$^circ$, 0.9$^circ$), spanning an area of 216.2
deg$^2$. This detection gap spatially coincides with the Cygnus X region $–$ a
plasma-rich star-forming region in the Milky Way. This lack of FRB detections
is most likely the result of increased sky temperature and strong multi-path
scattering by turbulent ionized plasma, which broadens the FRB signals beyond
detectability in the CHIME band. Our simulations yield a mean of 6 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 $tau_rm sc,, 1,GHz geq 4.13$ ms is sufficient to
suppress the observed signal-to-noise ratio of all FRBs. In addition to Cygnus
X, a similar suppression is seen in Catalog 2 along other high-emission measure
(EM) sightlines ( i.e., EM$geq$2900 pc cm$^-6$), further supporting a
broader trend of suppression due to Galactic scattering. Future very long
baseline interferometry (VLBI) measurements of scattering disks with CHIME
Outriggers could help confirm our interpretation. Our work highlights the
substantial impact of the ionized and turbulent Galactic interstellar medium on
the detectability of FRBs.
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