Kavli Affiliate: Kiyoshi W. Masui
| First 5 Authors: Hsiu-Hsien Lin, Paul Scholz, Cherry Ng, Ue-Li Pen, Mohit Bhardwaj
| Summary:
We report ten fast radio bursts (FRBs) detected in the far side-lobe region
(i.e., $geq 5^circ$ off-meridian) of the Canadian Hydrogen Intensity Mapping
Experiment (CHIME) from 2018 August 28 to 2021 August 31. We localize the
bursts by fitting their spectra with a model of the CHIME/FRB synthesized beam
response. We find that the far side-lobe events have on average ~500 times
greater fluxes than events detected in CHIME’s main lobe. We show that the
side-lobe sample is therefore statistically ~20 times closer than the main-lobe
sample. We find promising host galaxy candidates (P$_{rm cc}$ < 1%) for two of
the FRBs, 20190112B and 20210310B, at distances of 38 and 16 Mpc, respectively.
CHIME/FRB did not observe repetition of similar brightness from the uniform
sample of 10 side-lobe FRBs in a total exposure time of 35580 hours. Under the
assumption of Poisson-distributed bursts, we infer that the mean repetition
interval above the detection threshold of the far side-lobe events is longer
than 11880 hours, which is at least 2380 times larger than the interval from
known CHIME/FRB detected repeating sources, with some caveats, notably that
very narrow-band events could have been missed. Our results from these far
side-lobe events suggest one of two scenarios: either (1) all FRBs repeat and
the repetition intervals span a wide range, with high-rate repeaters being a
rare subpopulation, or (2) non-repeating FRBs are a distinct population
different from known repeaters.
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