The birth of the first luminous sources and the ensuing epoch of reionization are best studied via the redshifted 21-cm emission line, the signature of the first two imprinting the last. In this ...work, we present a fully Bayesian method, hibayes, for extracting the faint, global (sky-averaged) 21-cm signal from the much brighter foreground emission. We show that a simplified (but plausible) Gaussian model of the 21-cm emission from the Cosmic Dawn epoch (15 ≲ z ≲ 30), parametrized by an amplitude
$A_{\rm H\,\small {I}}$
, a frequency peak
$\nu _{\rm H\,\small {I}}$
and a width
$\sigma _{\rm H\,\small {I}}$
, can be extracted even in the presence of a structured foreground frequency spectrum (parametrized as a seventh-order polynomial), provided sufficient signal-to-noise (400 h of observation with a single dipole). We apply our method to an early, 19-min-long observation from the Large aperture Experiment to detect the Dark Ages, constraining the 21-cm signal amplitude and width to be
$-890 \lt A_{\rm H\,\small {I}} \lt 0$
mK and
$\sigma _{\rm H\,\small {I}} \gt 6.5$
MHz (corresponding to Δz > 1.9 at redshift z ≃ 20) respectively at the 95-per cent confidence level in the range 13.2 < z < 27.4 (100 > ν > 50 MHz).
ABSTRACT
The Large-aperture Experiment to detect the Dark Age (LEDA) was designed to measure the 21-cm signal from neutral hydrogen at Cosmic Dawn, z ≈ 15–30. Using observations made with the ≈ 200 m ...diameter core of the Owens Valley Radio Observatory Long Wavelength Array (OVRO–LWA), we present a 2D cylindrical spatial power spectrum for data at 43.1–53.5 MHz (zmedian ≈ 28) incoherently integrated for 4 h, and an analysis of the array sensitivity. Power from foregrounds is localized to a ‘wedge’ within k⊥, $k_\parallel$ space. After calibration of visibilities using five bright compact sources including Vir A, we measure Δ2(k) ≈ 2 × 1012 mK2 outside the foreground wedge, where an uncontaminated cosmological signal would lie, in principle. The measured Δ2(k) is an upper limit that reflects a combination of thermal instrumental and sky noise, and unmodelled systematics that scatter power from the wedge, as will be discussed. By differencing calibrated visibilities for close pairs of frequency channels, we suppress foreground sky structure and systematics, extract thermal noise, and use a mix of coherent and incoherent integration to simulate a noise-dominated power spectrum for a 3000 h observation and z = 16−37. For suitable calibration quality, the resulting noise level, Δ2(k) ≈ 100 mK2 (k = 0.3 Mpc−1), would be sufficient to detect peaks in the 21-cm spatial power spectrum due to early Ly-α and X-ray sources, as predicted for a range of theoretical model parameters.
We present results of the coordinated observing campaign that made the first subarcsecond localization of a fast radio burst, FRB 121102. During this campaign, we made the first simultaneous ...detection of an FRB burst using multiple telescopes: the VLA at 3 GHz and the Arecibo Observatory at 1.4 GHz. Of the nine bursts detected by the Very Large Array at 3 GHz, four had simultaneous observing coverage at other observatories at frequencies from 70 MHz to 15 GHz. The one multi-observatory detection and three non-detections of bursts seen at 3 GHz confirm earlier results showing that burst spectra are not well modeled by a power law. We find that burst spectra are characterized by a ∼500 MHz envelope and apparent radio energy as high as 1040 erg. We measure significant changes in the apparent dispersion between bursts that can be attributed to frequency-dependent profiles or some other intrinsic burst structure that adds a systematic error to the estimate of dispersion measure by up to 1%. We use FRB 121102 as a prototype of the FRB class to estimate a volumetric birth rate of FRB sources Mpc−3 yr−1, where Nr is the number of bursts per source over its lifetime. This rate is broadly consistent with models of FRBs from young pulsars or magnetars born in superluminous supernovae or long gamma-ray bursts if the typical FRB repeats on the order of thousands of times during its lifetime.
ABSTRACT
Total-power radiometry with individual meter-wave antennas is a potentially effective way to study the Cosmic Dawn (z ∼ 20) through measurement of the sky brightness arising from the 21 cm ...transition of neutral hydrogen, provided this can be disentangled from much stronger Galactic and extra-galactic foregrounds. In the process, measured spectra of integrated sky brightness temperature can be used to quantify the foreground emission properties. In this work, we analyse a subset of data from the Large-aperture Experiment to Detect the Dark Age (LEDA) in the 50–87 MHz range and constrain the foreground spectral index β in the northern sky visible from mid-latitudes. We focus on two zenith-directed LEDA radiometers and study how estimates of β vary with local sidereal time (LST). We correct for the effect of gain pattern chromaticity and compare estimated absolute temperatures with simulations. We select a reference data set consisting of 14 d of observations in optimal conditions. Using this data set, we find, for one radiometer, that β varies from −2.55 at LST <6 h to a steeper −2.58 at LST ∼13 h, consistently with sky models and previous southern sky measurements. In the 13 − 24 h LST range, however, we find that β varies between −2.55 and −2.61 (data scatter ∼0.01). We observe a similar β versus LST trend for the second radiometer, although with slightly smaller |β| over the 24 h, in the −2.46 < β < −2.43 range (data scatter ∼ 0.02). Combining all data gathered during the extended campaign between mid-2018 and mid-2019, and focusing on the LST = 9−12.5 h range, we infer good instrument stability and find −2.56 < β < −2.50 with 0.09 < Δβ < 0.12.
Background
Patients with cancer are increasingly offered genomic sequencing, including germline testing for cancer predisposition or other disorders. Such testing is unfamiliar to patients and ...families, and clear communication is needed to introduce genomic concepts and convey risk and benefit information.
Methods
Parents of children with cancer were offered the opportunity to have their children’s tumor and germline examined with clinical genomic sequencing. Families were introduced to the study with a 2‐visit informed consent model. Baseline genetic knowledge and self‐reported literacy/numeracy were collected before a study introduction visit, during which basic concepts related to genomic sequencing were discussed. Information was reinforced during a second visit, during which informed consent was obtained and a posttest was administered.
Results
As reflected by the percentage of correct answers on the pretest and posttest assessments, this model increased genetic knowledge by 11.1% (from 77.8% to 88.9%; P < .0001) in 121 parents participating in both the study introduction and consent visits. The percentage of parents correctly identifying the meaning of somatic and germline mutations increased significantly (from 18% to 59% somatic and from 31% to 64% germline; P < .0001). Nevertheless, these concepts remained unfamiliar to one‐third of the parents. No relation was identified between the change in the overall percentage of correct answers and self‐reported literacy, numeracy, or demographics.
Conclusions
The use of a 2‐visit communication model improved knowledge of concepts relevant to genomic sequencing, particularly differences between somatic and germline testing; however, these areas remained confusing to many participants, and reinforcement may be necessary to achieve complete understanding.
Quality informed consent begins with an adequate understanding of concepts relevant to the decision. A 2‐visit consent model using structured communication about genomic sequencing can increase baseline genetic knowledge in parents of children with cancer.
ABSTRACT The utility of Faraday rotation to measure the magnetic field of the solar corona and large-scale transients within is a small, yet growing field in solar physics. This is largely because it ...has been recognized as a potentially valuable frontier in space weather studies, because the ability to measure the intrinsic magnetic field within coronal mass ejections (CMEs) when they are close to the Sun is of great interest for understanding a key element of space weather. Such measurements have been attempted over the last few decades using radio signals from artificial sources (i.e., spacecraft on the far side of the Sun), but studies involving natural radio sources are scarce in the literature. We report on a preliminary study involving an attempt to detect the Faraday rotation of a CME that passed in front of a pulsar (PSR B0950+08) in 2015 August. We combine radio measurements with those from a broadband visible light coronagraph, to estimate the upper limit of the magnetic field of the CME when it was in the corona. We find agreement between different approaches for obtaining its density, and values that are consistent with those predicted from prior studies of CME density close to the Sun.
ABSTRACT
Efforts are underway to use high-precision timing of pulsars in order to detect low-frequency gravitational waves. A limit to this technique is the timing noise generated by dispersion in ...the plasma along the line of sight to the pulsar, including the solar wind. The effects due to the solar wind vary with time, influenced by the change in solar activity on different time-scales, ranging up to ∼11 yr for a solar cycle. The solar wind contribution depends strongly on the angle between the pulsar line of sight and the solar disc, and is a dominant effect at small separations. Although solar wind models to mitigate these effects do exist, they do not account for all the effects of the solar wind and its temporal changes. Since low-frequency pulsar observations are most sensitive to these dispersive delays, they are most suited to test the efficacy of these models and identify alternative approaches. Here, we investigate the efficacy of some solar wind models commonly used in pulsar timing using long-term, high-cadence data on six pulsars taken with the Long Wavelength Array, and compare them with an operational solar wind model. Our results show that stationary models of the solar wind correction are insufficient to achieve the timing noise desired by pulsar timing experiments, and we need to use non-stationary models, which are informed by other solar wind observations, to obtain accurate timing residuals.
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