Colliding winds in massive binaries generate X-ray-bright shocks, synchrotron radio emission, and sometimes even dusty "pinwheel" spirals. We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27 yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf-Rayet wind self-absorption and near-transparent O-star wind foreground each 20 yr orbit, producing phase-locked radio and X-ray variability. This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to similar to 1350 km s-1 in about one orbital cycle, naturally matching the IR spiral from 5 '' down to within 0 .'' 1, while also fitting the phase of the radio brightening. These kinematic constraints supply critical boundary conditions for future hydrodynamic simulations, which can link hot-plasma cooling, nonthermal radio emission, X-ray spectra, and dust formation in a self-consistent framework. WR 112 thus joins WR 140, WR 104, and WR 70-16 (Apep) as a benchmark system for testing colliding-wind physics under an increasingly diverse range of orbital architectures and physical conditions.

Abstract Reading impairment has been empirically associated with advantages for certain specific skills involved in the analysis of images, and given that astronomy is a highly visual science, we investigated whether such capabilities may be enhanced among astronomers. Here we examined the visuospatial abilities of 30 astrophysicists with and without a reading impairment, and compared their response with those of 74 high school students (novices). The task involved the analysis of simulated microwave spectra. (The angular span of the spectra was varied as a condition in the experiment.) As expected, the professional astrophysicists outperformed the novices, but while the performance of novices deteriorated as the span angle was broadened, performance improved in the experts. Notably, this contrast between expert and novice was especially pronounced in the scientists with a reading impairment, suggesting that those with a reading impairment may use different strategies for visual processing. (No such effects of reading impairment were observed in the novices.) In a second study, we administered a survey [Lefly Pennington(2000)] examining the incidence of reading impairment among 148 professional astrophysicists at the Harvard Smithsonian Center for Astrophysics (CfA) and 75 similarly accomplished academics at the Harvard Business School (HBS), selected at random. We found that, depending on the criteria used for reading impairment, the incidence of reading impairment is considerably higher among astronomy professionals compared with academics in business. Together, these studies suggest that astrophysics is a profession favorable to those with a reading impairment.

Radiometer experiments to detect 21-cm Hydrogen line emission from the Cosmic Dawn and Epoch of Reionization rely upon precise absolute calibration. Noise generated by amplifiers within the radiometer receiver must be accounted for; however, it is difficult to measure as the noise power varies with source impedance. In this letter, we introduce a convenient method to measure the noise parameters of a receiver system, which is practical for low-frequency receivers used in global 21-cm experiments.

Radiometer experiments to detect 21-cm Hydrogen line emission from the Cosmic Dawn and Epoch of Reionization rely upon precise absolute calibration. During calibration, noise generated by amplifiers within the radiometer receiver must be accounted for; however, it is difficult to measure as the noise power varies with source impedance. In this letter, we introduce a convenient method to measure the noise parameters of a receiver system, which is practical for low-frequency receivers used in global 21-cm experiments.

Noise parameters are a set of four measurable quantities which determine the noise performance of a radio frequency device under test (DUT). The noise parameters of a two-port device can be extracted by connecting a set of four or more source impedances at the device’s input, measuring the noise power of the device with each source connected, and then solving a matrix equation. However, sources with high reflection coefficients ( $|\Gamma |\approx 1$ ) cannot be used due to a singularity that arises in entries of the matrix. Here, we detail a new method of noise parameter extraction using a singularity-free matrix that is compatible with high-reflection sources. We show that open, short, load, and an open cable (OSLC) can be used to extract noise parameters and detail a practical measurement approach. The OSLC approach is particularly well-suited for low-noise amplifiers at frequencies below 1 GHz, where alternative methods require physically large apparatus.

Cosmic Dawn, the onset of star formation in the early universe, can in principle be studied via the 21cm transition of neutral hydrogen, for which a sky-averaged absorption signal, redshifted to MHz frequencies, is predicted to be O(10-100) mK. Detection requires separation of the 21cm signal from bright chromatic foreground emission due to Galactic structure, and the characterisation of how it couples to instrumental response. In this work, we present characterisation of antenna gain patterns for the Large-aperture Experiment to detect the Dark Ages (LEDA) via simulations, assessing the effects of the antenna ground-plane geometries used, and measured soil properties. We then investigate the impact of beam pattern uncertainties on the reconstruction of a Gaussian absorption feature. Assuming the pattern is known and correcting for the chromaticity of the instrument, the foregrounds can be modelled with a log-polynomial, and the 21cm signal identified with high accuracy. However, uncertainties on the soil properties lead to ‰ changes in the chromaticity that can bias the signal recovery. The bias can be up to a factor of two in amplitude and up to few per cent in the frequency location. These effects do not appear to be mitigated by larger ground planes, conversely gain patterns with larger ground planes exhibit more complex frequency structure, significantly compromising the parameter reconstruction. Our results, consistent with findings from other antenna design studies, emphasise the importance of chromatic response and suggest caution in assuming log-polynomial foreground models in global signal experiments.

Total power radiometry with individual meter-wave antennas is a potentially effective means to detect the brightness temperature from the 21 cm line of neutral hydrogen during the Cosmic Dawn. In the process, spectra of integrated sky brightness temperature can be used to quantify properties of foreground emission. In this work we analyze a subset of data from the Large-aperture Experiment to Detect the Dark Age (LEDA) and constrain the spectral index β of foreground emission in the northern sky. We correct for the effect of gain pattern chromaticity and compare estimated absolute temperatures with simulations. We estimate variation in β with local sidereal time (LST) using two widely spaced, zenith-directed radiometers during May and December 2018, and January-May 2019. For times in the 9-12.5h LST window when the Sun is not in the Sky and the Galactic Center is at least 20° below the local horizon’ we estimate β=-2.48\pm 0.07 for the first antenna, and β=-2.57+0.12 for the second. These results are consistent with previous measurements of the southern sky. Anomalously heavy rainstorms moved through the observing site in winter 2019. The coincident timing of episodic shifts in the temperature scales of the two radiometers suggests substantial sensitivity to the the changes in the soil moisture profile, though other variables may also be involved. We extend the analysis December/January data, for which soil conditions are optimal, to an almost 24 h LST range finding results in agreement with simulated sky models.

by M. Spinelli ,1,2‹ G. Bernardi,3,4,5 H. Garsden,6 L. J. Greenhill,6 A. Fialkov,7,8 J. Dowell 9 and D. C. Price 6,10 1INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34143 Trieste, Italy 2IFPU – Institute for Fundamental Physics of the Universe, Via Beirut 2, I-34014 Trieste, Italy 3INAF – Istituto di Radioastronomia, via Gobetti 101, I-40129, Bologna, Italy 4Department of Physics and Electronics, Artillery Road, Rhodes University, Grahamstown 6140, South Africa 5South African Radio Astronomy Observatory, FIR street, Observatory, Cape Town, South Africa 6Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge MA 02138, USA 7Kavli Institute for Cosmology, Madingley Road, Cambridge CB3 0HA, UK 8Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 9University of New Mexico, 1919 Lomas Boulevard NE, Albuquerque, NM 87131, USA 10International Centre for Radio Astronomy Research, Curtin University, Bentley WA 6102, Australia

We present the first results of a solar radio event observed with the Owens Valley Radio Observatory Long Wavelength Array at metric wavelengths. We examine a complex event consisting of multiple radio sources/bursts associated with a fast coronal mass ejection (CME) and an M2.1 GOES soft X-ray flare from 2015 September 20. Images of 9 s cadence are used to analyze the event over a 120 minute period, and solar emission is observed out to a distance of ≈3.5 R ⊙ , with an instantaneous bandwidth covering 22 MHz within the frequency range of 40–70 MHz. We present our results from the investigation of the radio event, focusing particularly on one burst source that exhibits outward motion, which we classify as a moving type IV burst. We image the event at multiple frequencies and use the source centroids to obtain the velocity for the outward motion. Spatial and temporal comparison with observations of the CME in white light from the C2 coronagraph of the Large Angle and Spectrometric COronagraph, indicates an association of the outward motion with the core of the CME. By performing graduated-cylindrical-shell reconstruction of the CME, we constrain the density in the volume. The electron plasma frequency obtained from the density estimates do not allow us to completely dismiss plasma emission as the underlying mechanism. However, based on source height and smoothness of the emission in frequency and time, we argue that gyrosynchrotron is the more plausible mechanism. We use gyrosynchrotron spectral-fitting techniques to estimate the evolving physical conditions during the outward motion of this burst source.

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 ≈ 200m diameter core of the Owens Valley Long Wavelength Array (OVRO-LWA), we present a 2-D cylindrical spatial power spectrum for data at 43.1-53.5 MHz (zmedian ≈ 28) incoherently integrated for 4 hours, and an analysis of the array sensitivity. Power from foregrounds is localized to a “wedge” within k⊥, k ‖ space. After calibration of visibilities using 5 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.

Maximally Smooth Functions (MSFs) are a form of constrained functions in which there are no inflection points or zero crossings in high order derivatives. Consequently, they have applications to signal recovery in experiments where signals of interest are expected to be non-smooth features masked by larger smooth signals or foregrounds. They can also act as a powerful tool for diagnosing the presence of systematics. The constrained nature of MSFs makes fitting these functions a non-trivial task. We introduce maxsmooth, an open source package that uses quadratic programming to rapidly fit MSFs. We demonstrate the efficiency and reliability of maxsmooth by comparison to commonly used fitting routines and show that we can reduce the fitting time by approximately two orders of magnitude. We introduce and implement with maxsmooth Partially Smooth Functions, which are useful for describing elements of non-smooth structure in foregrounds. This work has been motivated by the problem of foreground modelling in 21-cm cosmology. We discuss applications of maxsmooth to 21-cm cosmology and highlight this with examples using data from the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) and the Large-aperture Experiment to Detect the Dark Ages (LEDA) experiments. We demonstrate the presence of a sinusoidal systematic in the EDGES data with a log-evidence difference of 86.19±0.12 when compared to a pure foreground fit. MSFs are applied to data from LEDA for the first time in this paper and we identify the presence of sinusoidal systematics. maxsmooth is pip installable and available for download at: https://github.com/htjb/maxsmooth

A successful ground array Radio Frequency (RF)-only self-trigger is demonstrated with 256 dual-polarization antennas of the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA), yielding 10 high-energy cosmic ray candidates. This RF-only capability is predicated on novel techniques for Radio Frequency Interference (RFI) identification and mitigation with an analysis efficiency of approximately 45% for shower-driven events with a Signal-to-noise ratio ≳ 5 against the galactic background noise power of individual antennas. Radio self-triggering enables more efficient detection of cosmic rays over a wider range of zenith angles than possible via triggers from in-situ particle detectors and the method presented here can be easily adapted to neutrino experiments relying on RF-only detection. This paper discusses the system design, RFI characterization and mitigation techniques, and initial results from 10 cosmic ray candidate events identified within a 40-hour observing window. A design for a future optimized commensal cosmic-ray detector for the OVRO-LWA is presented, as well as recommendations for developing a similar capability for other experiments — these designs either reduce data-rate or increase sensitivity by an order of magnitude for many configurations of radio instruments.

We present a multiwavelength study of the active galactic nucleus in the nearby (D = 14.1 Mpc) low-mass galaxy IC 750, which has circumnuclear 22 GHz water maser emission. The masers trace a nearly edge-on, warped disk similar to 0.2 pc in diameter, coincident with the compact nuclear X-ray source that lies at the base of the similar to kiloparsec-scale extended X-ray emission. The position-velocity structure of the maser emission indicates that the central black hole (BH) has a mass less than 1.4 x 10(5) M-circle dot. Keplerian rotation curves fitted to these data yield enclosed masses between 4.1x10(4)M(circle dot) and 1.4x10(5)M(circle dot), with a mode of 7.2x10(4) M-circle dot. Fitting the optical spectrum, we measure a nuclear stellar velocity dispersion sigma(*) = 110.7 -(12.1)(13.4)s(-1). From near-infrared photometry, we fit a bulge mass of (7.3 +/- 2.7) x 10(8) M-circle dot and a stellar mass of 1.4 x 10(10)M(circle dot). The mass upper limit of the intermediate-mass BH in IC 750 falls roughly two orders of magnitude below the M-BH-=M-* relation M-BH-M-Bulge and M-BH-M-* relations-larger than the relations' intrinsic scatters of 0.58 0.09 dex, 0.69 dex, and 0.65 0.09 dex, respectively. These offsets could be due to larger scatter at the low-mass end of these relations. Alternatively, BH growth is intrinsically inefficient in galaxies with low bulge and/or stellar masses, which causes the BHs to be undermassive relative to their hosts, as predicted by some galaxy evolution simulations.

The 21 cm transition of neutral hydrogen is opening an observational window into the Cosmic Dawn of the universe-the epoch of first star formation. We use 28 hr of data from the Owens Valley Radio Observatory Long Wavelength Array to place upper limits on the spatial power spectrum of 21 cm emission at z approximate to 18.4 (Delta 21 less than or similar to 10(4) mK), and within the absorption feature reported by the EDGES experiment. In the process we demonstrate the first application of the double Karhunen-Loeve transform for foreground filtering, and diagnose the systematic errors that are currently limiting the measurement. We also provide an updated model for the angular power spectrum of low-frequency foreground emission measured from the northern hemisphere, which can be used to refine sensitivity forecasts for next-generation experiments.

We report on a search for low-frequency radio variability in 944 bright (>4 Jy at 154 MHz) unresolved, extragalactic radio sources monitored monthly for several years with the Murchison Widefield Array. In the majority of sources, we find very low levels of variability with typical modulation indices <5 per cent. We detect 15 candidate low-frequency variables that show significant long-term variability (>2.8 yr) with time-averaged modulation indices (M) over bar = 3.1-7.1 per cent. With 7/15 of these variable sources having peaked spectral energy distributions, and only 5.7 per cent of the overall sample having peaked spectra, we find an increase in the prevalence of variability in this spectral class. We conclude that the variability seen in this survey is most probably a consequence of refractive interstellar scintillation and that these objects must have the majority of their flux density contained within angular diameters less than 50 milliarcsec (which we support with multiwavelength data). At 154 MHz, we demonstrate that interstellar scintillation time-scales become long (similar to decades) and have low modulation indices, while synchrotron-driven variability can only produce dynamic changes on time-scales of hundreds of years, with flux density changes less than one milli-jansky (without relativistic boosting). From this work, we infer that the low-frequency extragalactic southern sky, as seen by SKA-Low, will be non-variable on time-scales shorter than 1 yr.

A dual beam, dual polarization, low noise receiver has been installed at a Cassegrain focus of the NASA 70[Formula: see text]m antenna near Canberra, Australia. It operates in five pairs of 1[Formula: see text]GHz bands from 17 to 27[Formula: see text]GHz simultaneously. The receiver temperature measured at the feed is 21–22[Formula: see text]K at 22[Formula: see text]GHz and, during dry winter night-time conditions, zenith system temperatures as low as 35[Formula: see text]K have been observed in the 21–22[Formula: see text]GHz band. The native polarization is linear but can be converted to circular prior to down-conversion. The downconverters have complex mixers, followed by quadrature hybrids which can be bypassed or used to convert the quadrature phase channels into an upper and lower sideband, each 1000[Formula: see text]MHz wide. For spectroscopy, four ROACH1 signal processors each currently providing 32[Formula: see text]K channel spectra across four 1000[Formula: see text]MHz bands, for 0.4[Formula: see text]km/s velocity resolution at 22[Formula: see text]GHz. Using both beam- and position-switching, the receiver achieved a noise level of 5[Formula: see text]mK r.m.s. in an hour of integration and 31[Formula: see text]kHz resolution. The NASA 70[Formula: see text]m antennas have a 45 arcsec beamwidth at 22[Formula: see text]GHz and an aperture efficiency of 35.5% giving a sensitivity of 0.49[Formula: see text]K/Jy.

We have conducted the most sensitive low-frequency (below 100 MHz) search to date for prompt, low-frequency radio emission associated with short-duration gamma-ray bursts (GRBs), using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). The OVRO-LWA's nearly full-hemisphere field of view (similar to 20,000 square degrees) allows us to search for low-frequency (sub-100 MHz) counterparts for a large sample of the subset of GRB events for which prompt radio emission has been predicted. Following the detection of short GRB 170112A by Swift, we used all-sky OVRO-LWA images spanning one hour prior to and two hours following the GRB event to search for a transient source coincident with the position of GRB 170112A. We detect no transient source to within a 3 sigma flux density limit of 4.5. Jy at 13 s timescales for frequencies spanning 27-84. MHz. We place constraints on a number of models predicting prompt, low-frequency radio emission accompanying short GRBs and their potential binary neutron star merger progenitors, and place an upper limit of L-radio/L gamma less than or similar to 3.5 x 10(-6) on the fraction of energy released in the prompt radio emission, under the assumptions of negligible scattering of the radio pulse and beaming of emission along the line of sight. These observations serve as a pilot effort for a program targeting a wider sample of both short and long GRBs with the OVRO-LWA, including bursts with confirmed redshift measurements that are critical to placing constraining limits on prompt radio emission models, as well as a program for the follow-up of gravitational wave compact binary coalescence events detected by advanced LIGO and Virgo.