ABSTRACT
We constrain the Hubble constant H0 using Fast Radio Burst (FRB) observations from the Australian Square Kilometre Array Pathfinder (ASKAP) and Murriyang (Parkes) radio telescopes. We use ...the redshift-dispersion measure (‘Macquart’) relationship, accounting for the intrinsic luminosity function, cosmological gas distribution, population evolution, host galaxy contributions to the dispersion measure (DMhost), and observational biases due to burst duration and telescope beamshape. Using an updated sample of 16 ASKAP FRBs detected by the Commensal Real-time ASKAP Fast Transients (CRAFT) Survey and localized to their host galaxies, and 60 unlocalized FRBs from Parkes and ASKAP, our best-fitting value of H0 is calculated to be $73_{-8}^{+12}$ km s−1 Mpc−1. Uncertainties in FRB energetics and DMhost produce larger uncertainties in the inferred value of H0 compared to previous FRB-based estimates. Using a prior on H0 covering the 67–74 km s−1 Mpc−1 range, we estimate a median ${\rm DM}_{\rm host}= 186_{-48}^{+59}\,{\rm pc \, cm^{-3}}$, exceeding previous estimates. We confirm that the FRB population evolves with redshift similarly to the star-formation rate. We use a Schechter luminosity function to constrain the maximum FRB energy to be log10Emax$=41.26_{-0.22}^{+0.27}$ erg assuming a characteristic FRB emission bandwidth of 1 GHz at 1.3 GHz, and the cumulative luminosity index to be $\gamma =-0.95_{-0.15}^{+0.18}$. We demonstrate with a sample of 100 mock FRBs that H0 can be measured with an uncertainty of ±2.5 km s−1 Mpc−1, demonstrating the potential for clarifying the Hubble tension with an upgraded ASKAP FRB search system. Last, we explore a range of sample and selection biases that affect FRB analyses.
PSR J0742−2822 exhibits two distinct emission states that are identified by discrete changes in the observed pulse profile. These changes have previously been shown to correlate with changes in the ...derivative of the pulse frequency. In this paper, we use observations with the Parkes radio telescope at a centre frequency of 1369 and 3100 MHz to produce high phase resolution polarization profiles for the two modes and perform a detailed study of the correlation between observed pulse shape and spin-down rate. We find no correlation for at least 200 d prior to a glitch in the pulsar at MJD 550 22, following which the correlation becomes strong. This suggests a link between the emission state switching phenomenon and glitch events. We discuss the possibility that emission state switching is driven by the interaction between the magnetosphere and the interior of the neutron star.
Abstract
Tillering and plant biomass are key determinants of rice crop productivity. Tillering at the vegetative stage is associated with weed competition, nutrient uptake, and methane emissions. ...However, little information is available on quantitative trait loci (QTLs) associated with tiller number (
qTN
), root biomass (
qRB
), and shoot biomass (
qSB
) at the active tillering stage which occurs approximately 6 weeks after planting. Here, we mapped tiller and biomass QTLs with ~ 250 recombinant inbred lines derived from a ‘Francis’ by ‘Rondo’ cross using data collected at the maximum tillering stage from two years of greenhouse study, and further compared these QTLs with those mapped at the harvest stage from a field study. Across these three studies, we discovered six
qTNs
, two
qRBs
, and three
qSBs
. Multiple linear regression further indicated that
qTN1-2
,
qTN3-3
,
qTN4-1
,
qRB3-1
, and
qRB5-1
were significant at the maximum tillering stage while
qTN3-2
was detected only at the harvest stage. Moreover,
qTN3-1
was consistently significant across different developmental stages and growing environments. The genes identified from the peak target
qTN
regions included a carotenoid metabolism enzyme, a MYB transcription factor, a CBS domain-containing protein, a SAC3/GANP family protein, a TIFY motif containing protein, and an ABC transporter protein. Two genes in the qRB peak target regions included an expressed protein and a WRKY gene. This knowledge of the QTLs, associated markers, candidate genes, and germplasm resources with high TN, RB and SB is of value to rice cultivar improvement programs.
We analyse dispersion measure (DM) variations in six years of radio observations of more than 160 young pulsars, all gamma-ray candidates for the Fermi gamma-ray telescope mostly located close to the ...Galactic plane. DMs were fitted across 256 MHz of bandwidth for observations centred at 1.4 GHz and across three frequencies - 0.7, 1.4 and 3.1 GHz - where multifrequency observations were available. Changes in dispersion measure, dDM/dt, were calculated using a weighted linear fit across all epochs of available DMs. DM variations were detected at a 3σ level in 11 pulsars, four of which were above 5σ: PSRs J0835−4510, J0908−4913, J1824−1945 and J1833−0827. We find that after 28 years of gradual decline, the DM of PSR J0835−4510 is now increasing. The magnitude of variations in three of the four (PSRs J0835−4510, J0908−4913 and J1833−0827) are above what models would predict for an interstellar medium (ISM) dominated by Kolmogorov turbulence. We attribute this excess as likely due to the pulsar's local environment - the supernova remnants near PSRs J0835−4510 and J1833−0827 and the pulsar wind nebula around PSR J0908−4913. Upper limits were determined for all pulsars without detectable values of dDM/dt, most limits were found to lie above the levels of variations predicted by ISM theory. We find our results to be consistent with scattering estimates from the NE2001 model along these lines of sight.
Development of a pulsar-based time-scale Hobbs, G; Coles, W; Manchester, R. N ...
Monthly notices of the Royal Astronomical Society,
21 December 2012, Letnik:
427, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Abstract
Using observations of pulsars from the Parkes Pulsar Timing Array (PPTA) project we develop the first pulsar-based time-scale that has a precision comparable to the uncertainties in ...International Atomic Time-scales (TAI). Our ensemble of pulsars provides an Ensemble Pulsar Scale (EPS) analogous to the free atomic time-scale Échelle Atomique Libre. The EPS can be used to detect fluctuations in atomic time-scales and therefore can lead to a new realization of Terrestrial Time, TT(PPTA11). We successfully follow features known to affect the frequency of the TAI, and we find marginally significant differences between TT(PPTA11) and TT(BIPM11). We discuss the various phenomena that lead to a correlated signal in the pulsar timing residuals and therefore limit the stability of the pulsar time-scale.
To obtain the most accurate pulse arrival times from radio pulsars, it is necessary to correct or mitigate the effects of the propagation of radio waves through the warm and ionized interstellar ...medium. We examine both the strength of propagation effects associated with large-scale electron-density variations and the methodology used to estimate infinite frequency arrival times. Using simulations of two-dimensional phase-varying screens, we assess the strength and non-stationarity of timing perturbations associated with large-scale density variations. We identify additional contributions to arrival times that are stochastic in both radio frequency and time and therefore not amenable to correction solely using times of arrival. We attribute this to the frequency dependence of the trajectories of the propagating radio waves. We find that this limits the efficacy of low-frequency (metre-wavelength) observations. Incorporating low-frequency pulsar observations into precision timing campaigns is increasingly problematic for pulsars with larger dispersion measures.
We present high signal-to-noise ratio, multifrequency polarization pulse profiles for 24 millisecond pulsars that are being observed as part of the Parkes Pulsar Timing Array project. The pulsars are ...observed in three bands, centred close to 730, 1400 and 3100 MHz, using a dual-band 10 cm/50 cm receiver and the central beam of the 20-cm multibeam receiver. Observations spanning approximately six years have been carefully calibrated and summed to produce high S/N profiles. This allows us to study the individual profile components and in particular how they evolve with frequency. We also identify previously undetected profile features. For many pulsars we show that pulsed emission extends across almost the entire pulse profile. The pulse component widths and component separations follow a complex evolution with frequency; in some cases these parameters increase and in other cases they decrease with increasing frequency. The evolution with frequency of the polarization properties of the profile is also non-trivial. We provide evidence that the pre- and post-cursors generally have higher fractional linear polarization than the main pulse. We have obtained the spectral index and rotation measure for each pulsar by fitting across all three observing bands. For the majority of pulsars, the spectra follow a single power-law and the position angles follow a ... relation, as expected. However, clear deviations are seen for some pulsars. We also present phase-resolved measurements of the spectral index, fractional linear polarization and rotation measure. All these properties are shown to vary systematically over the pulse profile. (ProQuest: ... denotes formulae/symbols omitted.)
ABSTRACT
The mechanism that produces fast radio burst (FRB) emission is poorly understood. Targeted monitoring of repeating FRB sources provides the opportunity to fully characterize the emission ...properties in a manner impossible with one-off bursts. Here, we report observations of the source of FRB 20201124A, with the Australian Square Kilometre Array Pathfinder (ASKAP) and the ultra-wideband low (UWL) receiver at the Parkes 64-m radio telescope (Murriyang). The source entered a period of emitting bright bursts during early 2021 April. We have detected 16 bursts from this source. One of the bursts detected with ASKAP is the brightest burst ever observed from a repeating FRB source with an inferred fluence of 640 ± 70 Jy ms. Of the five bursts detected with the Parkes UWL, none display any emission in the range 1.1–4 GHz. All UWL bursts are highly polarized, with their Faraday rotation measures (RMs) showing apparent variations. We obtain an average RM of −614 rad m−2 for this FRB source with a standard deviation of 16 rad m−2 in the UWL bursts. In one of the UWL bursts, we see evidence of significant circularly polarized emission with a fractional extent of 47 ± 1 per cent. Such a high degree of circular polarization has never been seen before in bursts from repeating FRB sources. We also see evidence for significant variation in the linear polarization position angle in the pulse profile of this UWL repeat burst. Models for repeat burst emission will need to account for the increasing diversity in the burst polarization properties.
The localization of fast radio bursts (FRBs) has been hindered by the poor angular resolution of the detection observations and inconclusive identification of transient or variable counterparts. ...Recently a γ-ray pulse of 380 s duration has been associated with FRB 131104. We report on radio-continuum imaging observations of the original localization region of the FRB, beginning three days after the event and comprising 25 epochs over 2.5 years. We argue that the probability of an association between the FRB and the γ-ray transient has been overestimated. We provide upper limits on radio afterglow emission that would be predicted if the γ-ray transient was associated with an energetic γ-ray burst. We further report the discovery of an unusual variable radio source spatially and temporally coincident with FRB 131104, but not spatially coincident with the γ-ray event. The radio variable flares by a factor of 3 above its long-term average within 10 day of the FRB at 7.5 GHz, with a factor-of-2 increase at 5.5 GHz. Since the flare, the variable has persisted with only modest modulation and never approached the flux density observed in the days after the FRB. We identify an optical counterpart to the variable. Optical and infrared photometry, and deep optical spectroscopy, suggest that the object is a narrow-line radio active galactic nucleus.
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