1,277 research outputs found
Probing motion of fast radio burst sources by timing strongly lensed repeaters
Given the possible repetitive nature of fast radio bursts (FRBs), their
cosmological origin, and their high occurrence, detection of strongly lensed
sources due to intervening galaxy lenses is possible with forthcoming radio
surveys. We show that if multiple images of a repeating source are resolved
with VLBI, using a method independent of lens modeling, accurate timing could
reveal non-uniform motion, either physical or apparent, of the emission spot.
This can probe the physical nature of FRBs and their surrounding environments,
constraining scenarios including orbital motion around a stellar companion if
FRBs require a compact star in a special system, and jet-medium interactions
for which the location of the emission spot may randomly vary. The high timing
precision possible for FRBs () compared to the typical time
delays between images in galaxy lensing () enables the
measurement of tiny fractional changes in the delays (), and
hence the detection of time-delay variations induced by relative motions
between the source, the lens, and the Earth. We show that uniform cosmic
peculiar velocities only cause the delay time to drift linearly, and that the
effect from the Earth's orbital motion can be accurately subtracted, thus
enabling a search for non-trivial source motion. For a timing accuracy of ms and a repetition rate (of detected bursts) per day of a
single FRB source, non-uniform displacement AU of the
emission spot perpendicular to the line of sight is detectable if repetitions
are seen over a period of hundreds of days.Comment: 21 pages, 6 figures, 1 table. New version accepted to ApJ with
abstract revised, typo corrected, and references adde
Implications from ASKAP Fast Radio Burst Statistics
Although there has recently been tremendous progress in studies of fast radio
bursts (FRBs), the nature of their progenitors remains a mystery. We study the
fluence and dispersion measure (DM) distributions of the ASKAP sample to better
understand their energetics and statistics. We first consider a simplified
model of a power-law volumetric rate per unit isotropic energy dN/dE ~
E^{-gamma} with a maximum energy E_max in a uniform Euclidean Universe. This
provides analytic insights for what can be learnt from these distributions. We
find that the observed cumulative DM distribution scales as N(>DM) ~
DM^{5-2*gamma} (for gamma > 1) until a maximum value DM_max above which bursts
near E_max fall below the fluence threshold of a given telescope. Comparing
this model with the observed fluence and DM distributions, we find a reasonable
fit for gamma ~ 1.7 and E_max ~ 10^{33} erg/Hz. We then carry out a full
Bayesian analysis based on a Schechter rate function with cosmological factor.
We find roughly consistent results with our analytical approach, although with
large errors on the inferred parameters due to the small sample size. The
power-law index and the maximum energy are constrained to be gamma = 1.6 +/-
0.3 and log(E_max) [erg/Hz] = 34.1 +1.1 -0.7 (68% confidence), respectively.
From the survey exposure time, we further infer a cumulative local volumetric
rate of log N(E > 10^{32} erg/Hz) [Gpc^{-3} yr^{-1}] = 2.6 +/- 0.4 (68%
confidence). The methods presented here will be useful for the much larger FRB
samples expected in the near future to study their distributions, energetics,
and rates.Comment: ApJ accepted. Expanded beyond the scope of the earlier version into 8
pages, 7 figures. Following referees' comments, we included a full Bayesian
analysis based on a Schechter rate function with cosmological factor. The PDF
of the inferred model parameters are presented by MCMC sampling in Figure 4
(the most important result). We also discussed the completeness of ASKAP
sample in Section
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