Lessons learned from CHIME repeating FRBs. (arXiv:2003.12581v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Lu_W/0/1/0/all/0/1">Wenbin Lu</a> (Caltech), <a href="http://arxiv.org/find/astro-ph/1/au:+Piro_A/0/1/0/all/0/1">Anthony L. Piro</a> (Carnegie Observatories), <a href="http://arxiv.org/find/astro-ph/1/au:+Waxman_E/0/1/0/all/0/1">Eli Waxman</a> (Weizmann Institute)
CHIME has now detected 18 repeating fast radio bursts (FRBs). We explore what
can be learned about the energy distribution and activity level of the
repeaters by constructing a realistic FRB population model, taking into account
wait-time clustering and cosmological effects. For a power-law energy
distribution dN/dE ~ E^{-gamma} for the repeating bursts, a steep energy
distribution means that most repeaters should be found in the local Universe
with low dispersion measure (DM), whereas a shallower distribution means some
repeaters may be detected at large distances with high DM. It is especially
interesting that there are two high-DM repeaters (FRB 181017 and 190417) with
DM ~ 1000 pc/cm^3. These can be understood if: (i) the energy distribution is
shallow gamma = 1.7 + 0.3 – 0.1 (68% confidence) or (ii) a small fraction of
sources are extremely active. In the second scenario, these high-DM sources
should be repeating more than 100 times more frequently than FRB 121102, and
the energy index is constrained to be gamma = 1.9 + 0.3 – 0.2 (68% confidence).
In either case, this power-law index is consistent with the energy dependence
of the non-repeating ASKAP sample, which suggests that they are drawn from the
same population. Finally, we show that the CHIME repeating fraction can be used
to infer the distribution of activity level in the whole population.
CHIME has now detected 18 repeating fast radio bursts (FRBs). We explore what
can be learned about the energy distribution and activity level of the
repeaters by constructing a realistic FRB population model, taking into account
wait-time clustering and cosmological effects. For a power-law energy
distribution dN/dE ~ E^{-gamma} for the repeating bursts, a steep energy
distribution means that most repeaters should be found in the local Universe
with low dispersion measure (DM), whereas a shallower distribution means some
repeaters may be detected at large distances with high DM. It is especially
interesting that there are two high-DM repeaters (FRB 181017 and 190417) with
DM ~ 1000 pc/cm^3. These can be understood if: (i) the energy distribution is
shallow gamma = 1.7 + 0.3 – 0.1 (68% confidence) or (ii) a small fraction of
sources are extremely active. In the second scenario, these high-DM sources
should be repeating more than 100 times more frequently than FRB 121102, and
the energy index is constrained to be gamma = 1.9 + 0.3 – 0.2 (68% confidence).
In either case, this power-law index is consistent with the energy dependence
of the non-repeating ASKAP sample, which suggests that they are drawn from the
same population. Finally, we show that the CHIME repeating fraction can be used
to infer the distribution of activity level in the whole population.
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