324 research outputs found
Five new real-time detections of Fast Radio Bursts with UTMOST
We detail a new fast radio burst (FRB) survey with the Molonglo Radio
Telescope, in which six FRBs were detected between June 2017 and December 2018.
By using a real-time FRB detection system, we captured raw voltages for five of
the six events, which allowed for coherent dedispersion and very high time
resolution (10.24 s) studies of the bursts. Five of the FRBs show temporal
broadening consistent with interstellar and/or intergalactic scattering, with
scattering timescales ranging from 0.16 to 29.1 ms. One burst, FRB181017, shows
remarkable temporal structure, with 3 peaks each separated by 1 ms. We searched
for phase-coherence between the leading and trailing peaks and found none,
ruling out lensing scenarios. Based on this survey, we calculate an all-sky
rate at 843 MHz of events sky day to a fluence
limit of 8 Jy-ms: a factor of 7 below the rates estimated from the Parkes and
ASKAP telescopes at 1.4 GHz assuming the ASKAP-derived spectral index
(). Our results suggest that FRB
spectra may turn over below 1 GHz. Optical, radio and X-ray followup has been
made for most of the reported bursts, with no associated transients found. No
repeat bursts were found in the survey.Comment: 13 pages, 11 figures, submitted to MNRA
Measuring the cosmic proper distance from fast radio bursts
The cosmic proper distance is a fundamental distance in the Universe.
Unlike the luminosity and angular diameter distances, which correspond to the
angular size, the proper distance is the length of light path from the source
to observer. However, the proper distance has not been measured before. The
recent redshift measurement of a repeat fast radio burst (FRB) can shed light
on the proper distance. We show that the proper distance-redshift relation can
indeed be derived from dispersion measures (DMs) of FRBs with measured
redshifts. From Monte Carlo simulations, we find that about 500 FRBs with DM
and redshift measurements can tightly constrain the proper distance-redshift
relation. We also show that the curvature of our Universe can be constrained
with a model-independent method using this derived proper distance-redshift
relation and the observed angular diameter distances. Owing to the high event
rate of FRBs, hundreds of FRBs can be discovered in the future by upcoming
instruments. The proper distance will play an important role in investigating
the accelerating expansion and the geometry of the Universe.Comment: 9 pages, 4 figures, proof versio
Frbs: Fuzzy Rule-Based Systems for Classification and Regression in R
Fuzzy rule-based systems (FRBSs) are a well-known method family within soft computing. They are based on fuzzy concepts to address complex real-world problems. We present the R package frbs which implements the most widely used FRBS models, namely, Mamdani and Takagi Sugeno Kang (TSK) ones, as well as some common variants. In addition a host of learning methods for FRBSs, where the models are constructed from data, are implemented. In this way, accurate and interpretable systems can be built for data analysis and modeling tasks. In this paper, we also provide some examples on the usage of the package and a comparison with other common classification and regression methods available in R.This work was supported in part by the Spanish Ministry of Science and Innovation (MICINN) under Projects TIN2009-14575, TIN2011-28488, TIN2013-47210-P, and P10-TIC-06858. Bergmeir held a scholarship from the Spanish Ministry of Education (MEC) of the \Programa de Formación del Profesorado Universitario (FPU)"
VOEvent Standard for Fast Radio Bursts
Fast radio bursts are a new class of transient radio phenomena currently
detected as millisecond radio pulses with very high dispersion measures. As new
radio surveys begin searching for FRBs a large population is expected to be
detected in real-time, triggering a range of multi-wavelength and
multi-messenger telescopes to search for repeating bursts and/or associated
emission. Here we propose a method for disseminating FRB triggers using Virtual
Observatory Events (VOEvents). This format was developed and is used
successfully for transient alerts across the electromagnetic spectrum and for
multi-messenger signals such as gravitational waves. In this paper we outline a
proposed VOEvent standard for FRBs that includes the essential parameters of
the event and where these parameters should be specified within the structure
of the event. An additional advantage to the use of VOEvents for FRBs is that
the events can automatically be ingested into the FRB Catalogue (FRBCAT)
enabling real-time updates for public use. We welcome feedback from the
community on the proposed standard outlined below and encourage those
interested to join the nascent working group forming around this topic.Comment: 11 pages, 2 figures, parameter definition table in appendi
The UTMOST Survey for Magnetars, Intermittent pulsars, RRATs and FRBs I: System description and overview
We describe the ongoing `Survey for Magnetars, Intermittent pulsars, Rotating
radio transients and Fast radio bursts' (SMIRF), performed using the newly
refurbished UTMOST telescope. SMIRF repeatedly sweeps the southern Galactic
plane performing real-time periodicity and single-pulse searches, and is the
first survey of its kind carried out with an interferometer. SMIRF is
facilitated by a robotic scheduler which is capable of fully autonomous
commensal operations. We report on the SMIRF observational parameters, the data
analysis methods, the survey's sensitivities to pulsars, techniques to mitigate
radio frequency interference and present some early survey results. UTMOST's
wide field of view permits a full sweep of the Galactic plane to be performed
every fortnight, two orders of magnitude faster than previous surveys. In the
six months of operations from January to June 2018, we have performed
sweeps of the Galactic plane with SMIRF. Notable blind re-detections include
the magnetar PSR J16224950, the RRAT PSR J09413942 and the eclipsing
pulsar PSR J17482446A. We also report the discovery of a new pulsar, PSR
J170554. Our follow-up of this pulsar with the UTMOST and Parkes telescopes
at an average flux limit of mJy and mJy respectively,
categorizes this as an intermittent pulsar with a high nulling fraction of Comment: Submitted to MNRAS, comments welcom
A Millisecond Interferometric Search for Fast Radio Bursts with the Very Large Array
We report on the first millisecond timescale radio interferometric search for
the new class of transient known as fast radio bursts (FRBs). We used the Very
Large Array (VLA) for a 166-hour, millisecond imaging campaign to detect and
precisely localize an FRB. We observed at 1.4 GHz and produced visibilities
with 5 ms time resolution over 256 MHz of bandwidth. Dedispersed images were
searched for transients with dispersion measures from 0 to 3000 pc/cm3. No
transients were detected in observations of high Galactic latitude fields taken
from September 2013 though October 2014. Observations of a known pulsar show
that images typically had a thermal-noise limited sensitivity of 120 mJy/beam
(8 sigma; Stokes I) in 5 ms and could detect and localize transients over a
wide field of view. Our nondetection limits the FRB rate to less than
7e4/sky/day (95% confidence) above a fluence limit of 1.2 Jy-ms. Assuming a
Euclidean flux distribution, the VLA rate limit is inconsistent with the
published rate of Thornton et al. We recalculate previously published rates
with a homogeneous consideration of the effects of primary beam attenuation,
dispersion, pulse width, and sky brightness. This revises the FRB rate downward
and shows that the VLA observations had a roughly 60% chance of detecting a
typical FRB and that a 95% confidence constraint would require roughly 500
hours of similar VLA observing. Our survey also limits the repetition rate of
an FRB to 2 times less than any known repeating millisecond radio transient.Comment: Submitted to ApJ. 13 pages, 9 figure
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