216 research outputs found
A Search for Fast Radio Bursts with the GBNCC Pulsar Survey
We report on a search for Fast Radio Bursts (FRBs) with the Green Bank
Northern Celestial Cap (GBNCC) Pulsar Survey at 350 MHz. Pointings amounting to
a total on-sky time of 61 days were searched to a DM of 3000 pc cm while
the rest (23 days; 29% of the total time) were searched to a DM of 500 pc
cm. No FRBs were detected in the pointings observed through May 2016. We
estimate a 95% confidence upper limit on the FRB rate of FRBs
sky day above a peak flux density of 0.63 Jy at 350 MHz for an
intrinsic pulse width of 5 ms. We place constraints on the spectral index
by running simulations for different astrophysical scenarios and
cumulative flux density distributions. The non-detection with GBNCC is
consistent with the 1.4-GHz rate reported for the Parkes surveys for in the absence of scattering and free-free absorption and in the presence of scattering, for a Euclidean flux distribution. The
constraints imply that FRBs exhibit either a flat spectrum or a spectral
turnover at frequencies above 400 MHz. These constraints also allow estimation
of the number of bursts that can be detected with current and upcoming surveys.
We predict that CHIME may detect anywhere from several to 50 FRBs a day
(depending on model assumptions), making it well suited for interesting
constraints on spectral index, the log -log slope and pulse profile
evolution across its bandwidth (400-800 MHz).Comment: 18 pages, 10 figures, Accepted for publication in Ap
Detection of Repeating FRB 180916.J0158+65 Down to Frequencies of 300 MHz
We report on the detection of seven bursts from the periodically active,
repeating fast radio burst (FRB) source FRB 180916.J0158+65 in the 300-400-MHz
frequency range with the Green Bank Telescope (GBT). Emission in multiple
bursts is visible down to the bottom of the GBT band, suggesting that the
cutoff frequency (if it exists) for FRB emission is lower than 300 MHz.
Observations were conducted during predicted periods of activity of the source,
and had simultaneous coverage with the Low Frequency Array (LOFAR) and the FRB
backend on the Canadian Hydrogen Intensity Mapping Experiment (CHIME)
telescope. We find that one of the GBT-detected bursts has potentially
associated emission in the CHIME band (400-800 MHz) but we detect no bursts in
the LOFAR band (110-190 MHz), placing a limit of on the
spectral index of broadband emission from the source. We also find that
emission from the source is severely band-limited with burst bandwidths as low
as 40 MHz. In addition, we place the strictest constraint on observable
scattering of the source, 1.7 ms, at 350 MHz, suggesting that the
circumburst environment does not have strong scattering properties.
Additionally, knowing that the circumburst environment is optically thin to
free-free absorption at 300 MHz, we find evidence against the association of a
hyper-compact HII region or a young supernova remnant (age 50 yr) with the
source.Comment: Accepted for publication in ApJ
A Distant Fast Radio Burst Associated with Its Host Galaxy by the Very Large Array
We present the discovery and subarcsecond localization of a new fast radio burst (FRB) by the Karl G. Jansky Very Large Array (VLA) and realfast search system. The FRB was discovered on 2019 June 14 with a dispersion measure of 959 pc cm⁻³. This is the highest DM of any localized FRB and its measured burst fluence of 0.6 Jy ms is less than nearly all other FRBs. The source is not detected to repeat in 15 hr of VLA observing and 153 hr of CHIME/FRB observing. We describe a suite of statistical and data quality tests we used to verify the significance of the event and its localization precision. Follow-up optical/infrared photometry with Keck and Gemini associate the FRB with a pair of galaxies with r ∼ 23 mag. The false-alarm rate for radio transients of this significance that are associated with a host galaxy is roughly 3×10⁻⁴ hr⁻¹. The two putative host galaxies have similar photometric redshifts of z_(phot) ∼ 0.6, but different colors and stellar masses. Comparing the host distance to that implied by the dispersion measure suggests a modest (~ 50 pc/cm⁻³) electron column density associated with the FRB environment or host galaxy/galaxies
LOFAR Detection of 110-188 MHz Emission and Frequency-Dependent Activity from FRB 20180916B
FRB 20180916B is a well-studied repeating fast radio burst source. Its
proximity (~150 Mpc), along with detailed studies of the bursts, have revealed
many clues about its nature -- including a 16.3-day periodicity in its
activity. Here we report on the detection of 18 bursts using LOFAR at 110-188
MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are
seen down to the lowest-observed frequency of 110 MHz, suggesting that their
spectra extend even lower. These observations provide an order-of-magnitude
stronger constraint on the optical depth due to free-free absorption in the
source's local environment. The absence of circular polarization and nearly
flat polarization angle curves are consistent with burst properties seen at
300-1700 MHz. Compared with higher frequencies, the larger burst widths
(~40-160 ms at 150 MHz) and lower linear polarization fractions are likely due
to scattering. We find ~2-3 rad/m^2 variations in the Faraday rotation measure
that may be correlated with the activity cycle of the source. We compare the
LOFAR burst arrival times to those of 38 previously published and 22 newly
detected bursts from the uGMRT (200-450 MHz) and CHIME/FRB (400-800 MHz).
Simultaneous observations show 5 CHIME/FRB bursts when no emission is detected
by LOFAR. We find that the burst activity is systematically delayed towards
lower frequencies by ~3 days from 600 MHz to 150 MHz. We discuss these results
in the context of a model in which FRB 20180916B is an interacting binary
system featuring a neutron star and high-mass stellar companion.Comment: Accepted for publication by ApJ
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