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The 230 GHz lightcurves of Sagittarius A* (Sgr A*) predicted by general relativistic magnetohydrodynamics and general relativistic ray-tracing (GRRT) models by the Event Horizon Telescope Collaboration have higher variability M Δ T compared to observations. In this series of papers, we explore the origin of such large brightness variability. In this first paper, we performed large GRRT parameter surveys that span from the optically thin to the optically thick regimes, covering the ion-to-electron temperature ratio under strongly magnetized conditions, R Low, from 1 to 60. We find that increasing R Low can lead to either an increase or a reduction in M Δ T depending on the other model parameters, making it consistent with the observed variability of Sgr A* in some cases. Our analysis of GRRT image snapshots finds that the major contribution to the large M Δ T for the R Low = 1 models comes from the photon ring. However, secondary contributions from the accretion flow are also visible depending on the spin parameter. Our work demonstrates the importance of the electron temperature used for modeling radiatively inefficient accretion flows and places new constraints on the ion-to-electron temperature ratio. A more in-depth analysis for understanding the dependencies of M Δ T on R Low will be performed in subsequent papers. [ABSTRACT FROM AUTHOR]

In this paper, a wideband Vivaldi phased array with double band-notched performance for radio astronomy is proposed. To address the issues of radio frequency interference from 5 G mobile communication (4.8–5 GHz) and C-band satellite communication (5.9–6.5 GHz) in radio astronomy system, the hairpin ring resonator (HRR), defected ground structure and λ/2 shorted-circuit stub are utilized together to realize the double notched bands with different bandwidth. The resonate mechanism of the proposed HRR is widely investigated, which exhibits independent and controllable resonances. Meanwhile, λ/2 shorted-circuited stub is adopted for the band notched performance. As the current on the stub is induced along the shorted via to the ground, without participating in radiation, thus the notched frequency is not affected by the scan angle. With these novel and dedicated design, the proposed phased array performs double band-notched performance with high skirt selectivity and deep suppression, within the notched band the maximum rejection level is better than 22.7 dB. This is the first work to implement double notched bands in phased array to the authors' best knowledge. Finally, a prototype composed of 8 × 9 elements is fabricated and measured. The measurements agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper studies how to employ synchrotron emission gradient techniques to reveal the properties of the magnetic field within the interstellar media. Based on data cubes of three-dimensional numerical simulations of magnetohydrodynamic turbulence, we explore spatial gradients of synchrotron emission diagnostics to trace the direction of the magnetic field. According to our simulations, multifarious diagnostics for synchrotron emission can effectively determine the potential direction of projected magnetic fields. Applying the synergies of synchrotron diagnostic gradients to the archive data from the Canadian Galactic Plane Survey, we find that multifarious diagnostic techniques make consistent predictions for the Galactic magnetic field directions. With the high-resolution data presently available from Low Frequency Array for radio astronomy and those in the future from the Square Kilometer Array, the synergies of synchrotron emission gradients are supposed to perform better in tracing the actual direction of interstellar magnetic fields, especially in the low-frequency Faraday rotation regime where the traditional synchrotron polarization measure fails. [ABSTRACT FROM AUTHOR]

The search for astronomical pulsed signals within noisy data in the radio band is usually performed through an initial Fourier analysis to find "candidate" frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a χ2 test to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the χ2 statistic has widely been replaced by the statistic and H-test, as they are more sensitive to extra information, such as the harmonic content of the pulsed profile. The statistic and H-test were originally developed for use with "event data" composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the statistic and H-test for pulse profiles with Gaussian uncertainties appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual χ2 method and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for radio frequency interference rejection. [ABSTRACT FROM AUTHOR]

The 230 GHz lightcurves of Sagittarius A* (Sgr A*) predicted by general relativistic magnetohydrodynamics and general relativistic ray-tracing (GRRT) models by the Event Horizon Telescope Collaboration have higher variability M _Δ _T compared to observations. In this series of papers, we explore the origin of such large brightness variability. In this first paper, we performed large GRRT parameter surveys that span from the optically thin to the optically thick regimes, covering the ion-to-electron temperature ratio under strongly magnetized conditions, R _Low , from 1 to 60. We find that increasing R _Low can lead to either an increase or a reduction in M _Δ _T depending on the other model parameters, making it consistent with the observed variability of Sgr A* in some cases. Our analysis of GRRT image snapshots finds that the major contribution to the large M _Δ _T for the R _Low = 1 models comes from the photon ring. However, secondary contributions from the accretion flow are also visible depending on the spin parameter. Our work demonstrates the importance of the electron temperature used for modeling radiatively inefficient accretion flows and places new constraints on the ion-to-electron temperature ratio. A more in-depth analysis for understanding the dependencies of M _Δ _T on R _Low will be performed in subsequent papers.

We report the discovery of three millisecond pulsars (MSPs): PSRs J1120âˆ'3618, J1646âˆ'2142, and J1828+0625 with the Giant Metrewave Radio Telescope (GMRT) at a frequency of 322 MHz using a 32 MHz observing bandwidth. These sources were discovered serendipitously while conducting the deep observations to search for millisecond radio pulsations in the directions of unidentified Fermi Large Area Telescope (LAT) Îł -ray sources. We also present phase coherent timing models for these MSPs using ∼5 yr of observations with the GMRT. PSR J1120âˆ'3618 has a 5.5 ms spin period and is in a binary system with an orbital period of 5.6 days and minimum companion mass of 0.18 M ⊙, PSR J1646âˆ'2142 is an isolated object with a spin period of 5.8 ms, and PSR J1828+0625 has a spin period of 3.6 ms and is in a binary system with an orbital period of 77.9 days and minimum companion mass of 0.27 M ⊙. The two binaries have very low orbital eccentricities, in agreement with expectations for MSP-helium white dwarf systems. Using the GMRT 607 MHz receivers having a 32 MHz bandwidth, we have also detected PSR J1646âˆ'2142 and PSR J1828+0625, but not PSR J1120âˆ'3618. PSR J1646âˆ'2142 has a wide profile, with significant evolution between 322 and 607 MHz, whereas PSR J1120âˆ'3618 exhibits a single peaked profile at 322 MHz and PSR J1828+0625 exhibits a single peaked profile at both the observing frequencies. These MSPs do not have Îł -ray counterparts, indicating that these are not associated with the target Fermi LAT pointing emphasizing the significance of deep blind searches for MSPs. [ABSTRACT FROM AUTHOR]

Solar type III radio bursts and their production mechanisms have been intensively studied in both theory and observation and are believed to be the most important signatures of electron acceleration in active regions. Recently, Wu et al. proposed that the electron-cyclotron maser emission (ECME) driven by an energetic electron beam could be responsible for producing type III bursts and pointed out that turbulent Alfvén waves can greatly influence the basic process of ECME via the oscillation of these electrons in the wave fields. This paper investigates effects of homochromous Alfvén waves (HAWs) on ECME driven by electron beams. Our results show that the growth rate of the O-mode wave will be significantly modulated by HAWs. We also discuss possible application to the formation of fine structures in type III bursts, such as so-called solar type IIIb radio bursts. [ABSTRACT FROM AUTHOR]

We report high angular resolution observations, made with the Atacama Large Millimeter Array in band 6, of high excitation molecular lines of CH 3 CN and SO2 and of the H29 α radio recombination line toward the G345.0061+01.794 B HC H ii region in order to investigate the physical and kinematical characteristics of its surroundings. Emission was detected in all observed components of the J = 14 →13 rotational ladder of CH 3 CN and in the 304,26–303,27, and 324,28–323,29 lines of SO2. The peak of the velocity-integrated molecular emission is located ∼0.″4 northwest of the peak of the continuum emission. The first-order moment images and channel maps show a velocity gradient of 1.1 km s−1 arcsec−1 across the source and a distinctive spot of blueshifted emission toward the peak of the zero-order moment. The rotational temperature is found to decrease from 252±24 K at the peak position to 166±16 K at its edge, indicating that our molecular observations are probing a hot molecular core that is internally excited. The emission in the H29 α line arises from a region of 0.″65 in size, where its peak coincides with that of the dust continuum. We model the kinematical characteristics of the "central blue spot" feature as due to infalling motions, suggesting a central mass of 172.8±8.8 M ⊙. Our observations indicate that this HC H ii region is surrounded by a compact structure of hot molecular gas, which is rotating and infalling toward a central mass, that is most likely confining the ionized region. The observed scenario is reminiscent of a "butterfly pattern" with an approximately edge-on torus and ionized gas roughly parallel to its rotation axis. [ABSTRACT FROM AUTHOR]

We present a new upper limit on the cosmic molecular gas density at z = 2.4–3.4 obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1–0) line emission of 0.129 Jy km s−1. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity L CO ′ of eBOSS quasars of ≤1.26 × 1011 K km pc2 s−1, or an average molecular gas density ρ H 2 in regions of the Universe containing a quasar of ≤1.52 × 108 M ⊙ cMpc−3. The L CO ′ upper limit falls among CO line luminosities obtained from individually targeted quasars in the COMAP redshift range, and the ρ H 2 value is comparable to upper limits obtained from other line intensity mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5 yr COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both as a technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data. [ABSTRACT FROM AUTHOR]

The noise performance of integrated low noise amplifiers (LNAs) is impaired by on-chip inductors owing to their low-quality factor, especially when inductors are used in the signal path at the input, such as for the inductively degenerated common-emitter amplifier. The inductively degenerated common-emitter configuration is largely used in LNA design, owing mainly to its ability to achieve impedance and noise matching simultaneously. This paper proposes an LNA configuration that achieves impedance matching and noise matching simultaneously without an inductor in the input signal path, owing to capacitive feedback and transistor sizing. Only the resistive component of the optimum noise resistance is matched to the source resistance. The impact of the mismatch due to the reactive component to the noise figure is reduced by the ratio Gs/Rn. A technique initially developed for the broadband matching of a single-layer microstrip patch antenna is used for the output matching network. Using a 130 nm silicon–germanium heterojunction bipolar transistor process, simulation results indicate a noise figure of 2.3 dB, a gain of 26 dB and S11 and S22 that are better than −12 dB at 1.42 GHz. This frequency corresponds to the 21 cm hydrogen line. This novel multi-stage LNA can be used for the detection of electromagnetic radiation from neutral hydrogen atoms from space in radio astronomy and the proposed design methodology can be generalized to LNAs. [ABSTRACT FROM AUTHOR]

The depth-dependent abundance of both gas-phase and solid-state water within dense, quiescent, molecular clouds is important to both the cloud chemistry and gas cooling. Where water is in the gas phase, it is free to participate in the network of ion-neutral reactions that lead to a host of oxygen-bearing molecules, and its many ortho- and para-energy levels make it an effective coolant for gas temperatures greater than 20 K. Where water is abundant as ice on grain surfaces, and unavailable to cool the gas, significant amounts of oxygen are removed from the gas phase, suppressing the gas-phase chemical reactions that lead to a number of oxygen-bearing species, including O2. Models of far-UV (FUV)-illuminated clouds predict that the gas-phase water abundance peaks in the range ∼ 3 and 8 mag of the cloud surface, depending on the gas density and FUV field strength. Deeper within such clouds, water is predicted to exist mainly as ice on grain surfaces. More broadly, these models are used to analyze a variety of other regions, including outflow cavities associated with young stellar objects and the surface layers of protoplanetary disks. In this paper, we report the results of observational tests of FUV-illuminated cloud models toward the Orion Molecular Ridge and Cepheus B using data obtained from the Herschel Space Observatory and the Five College Radio Astronomy Observatory. Toward Orion, 2220 spatial positions were observed along the face-on Orion Ridge in the H2O 1– 101 557 GHz and NH3J, K = 1,0–0,0 572 GHz lines. Toward Cepheus B, two strip scans were made in the same lines across the edge-on ionization front. These new observations demonstrate that gas-phase water exists primarily within a few magnitudes of dense cloud surfaces, strengthening the conclusions of an earlier study based on a much smaller data set, and indirectly supports the prediction that water ice is quite abundant in dense clouds. [ABSTRACT FROM AUTHOR]

Maximum Entropy is an image reconstruction method conceived to image a sparsely occupied field of view, therefore it is particularly effective at achieving super-resolution effects. Although widely used in image deconvolution, this method has been formulated in radio astronomy for the analysis of observations in the spatial frequency domain, and an Interactive Data Language code has been implemented for image reconstruction from solar X-ray Fourier data. However, this code relies on a non-convex formulation of the constrained optimization problem addressed by the Maximum Entropy approach, and this sometimes results in unreliable reconstructions characterized by unphysical shrinking effects. This paper introduces a new approach to Maximum Entropy based on the constrained minimization of a convex functional. In the case of observations recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), the resulting code provides the same super-resolution effects of the previous algorithm, while also working properly when that code produces unphysical reconstructions. We also obtain results via testing the algorithm with synthetic data simulating observations of the Spectrometer/Telescope for Imaging X-rays (STIX) in Solar Orbiter. The new code is available in the HESSI folder of the Solar SoftWare (SSW) tree. [ABSTRACT FROM AUTHOR]

We present the detection of a secondary outflow associated with a Class I source, Ser-emb 15, in the Serpens Molecular Cloud. We reveal two pairs of molecular outflows consisting of three lobes, that is, primary and secondary outflows, using Atacama Large Millimeter/submillimeter Array 12CO and SiO line observations at a resolution of ∼318 au. The secondary outflow is elongated approximately perpendicular to the axis of the primary outflow in the plane of the sky. We also identify two compact structures, Sources A and B, within an extended structure associated with Ser-emb 15 in the 1.3 mm continuum emission at a resolution of ∼40 au. The projected sizes of Sources A and B are 137 au and 60 au, respectively. Assuming a dust temperature of 20 K, we estimate the dust mass to be 2.4 × 10−3 M ⊙ for Source A and 3.3 × 10−4 M ⊙ for Source B. C18O line data imply rotational motion around the extended structure, but we cannot resolve rotational motion in Source A and/or B because the angular and frequency resolutions are insufficient. Therefore, we cannot conclude whether Ser-emb 15 is a single or binary system. Thus, either Source A or Source B could drive the secondary outflow. We discuss two scenarios that might explain the driving mechanism of the primary and secondary outflows: the Ser-emb 15 system is (1) a binary system composed of Sources A and B, or (2) a single-star system composed of Source A alone. In either case, the system could be a suitable target for investigating the disk and/or binary formation processes in complicated environments. Detecting these outflows should contribute to understanding complex star-forming environments, which may be common in the star formation processes. [ABSTRACT FROM AUTHOR]

We present the results of molecular line observations performed toward the NGC 2068 and NGC 2071 regions of the Orion B cloud as the TRAO-FUNS project to study the roles of the filamentary structure in the formation of dense cores and stars in the clouds. Gaussian decomposition for the C18O spectra with multiple velocity components and the application of a friends-of-friends algorithm for the decomposed components allowed us to identify a few tens of velocity-coherent filaments. We also identified 48 dense cores from the observations of N2H+ using a core finding tool, FellWalker. We performed a virial analysis for these filaments and dense cores, finding that the filaments with N2H+ dense core are thermally supercritical, and the filaments with a larger ratio between the line mass and the thermal critical line mass tend to have more dense cores. We investigated the contribution of the nonthermal motions in dense cores and filaments, showing the dense cores are mostly in transonic/subsonic motions while their natal filaments are mostly in supersonic motions. This may indicate that gas turbulent motions in the filaments have been dissipated at the core scale to form the dense cores there. The filaments with (dynamically evolved) dense cores in infalling motions or with NH2D bright (or chemically evolved) dense cores are all found to be gravitationally critical. Therefore, the criticality of the filament is thought to provide a key condition for its fragmentation, the formation of dense cores, and their kinematical and chemical evolution. [ABSTRACT FROM AUTHOR]

We present optical, near-infrared, and radio observations of supernova (SN) SN IIb 2022crv. We show that it retained a very thin H envelope and transitioned from an SN IIb to an SN Ib; prominent H α seen in the pre-maximum phase diminishes toward the post-maximum phase, while He i lines show increasing strength. SYNAPPS modeling of the early spectra of SN 2022crv suggests that the absorption feature at 6200 Å is explained by a substantial contribution of H α together with Si ii, as is also supported by the velocity evolution of H α. The light-curve evolution is consistent with the canonical stripped-envelope SN subclass but among the slowest. The light curve lacks the initial cooling phase and shows a bright main peak (peak M V = −17.82 ± 0.17 mag), mostly driven by radioactive decay of 56Ni. The light-curve analysis suggests a thin outer H envelope (M env ∼ 0.05 M ⊙) and a compact progenitor (R env ∼ 3 R ⊙). An interaction-powered synchrotron self-absorption model can reproduce the radio light curves with a mean shock velocity of 0.1 c. The mass-loss rate is estimated to be in the range of (1.9−2.8) × 10−5 M ⊙ yr−1 for an assumed wind velocity of 1000 km s−1, which is on the high end in comparison with other compact SNe IIb/Ib. SN 2022crv fills a previously unoccupied parameter space of a very compact progenitor, representing a beautiful continuity between the compact and extended progenitor scenario of SNe IIb/Ib. [ABSTRACT FROM AUTHOR]

Assuming civilizations have similar interplanetary communications and radar capability to NASA's Deep Space Network, what is the feasibility of intercepting their communications? Interplanetary conjunctions between Earth-like exoplanets, their stars, and other planets in their systems provide one of the most unique and pragmatic opportunities for detecting technosignatures. While eavesdropping on terrestrial communications becomes limited by a planet's rotation, the beams of satellite communications and interplanetary radar transmissions are tracked, providing the most persistent and powerful opportunity for signal interception. In this study, we present a framework for assessing exoplanet habitability and establishing quantitative bounds for detecting Earth-scale technosignatures from Earth-like planets. These constraints for time, frequency, sky positions, and observatory sensitivity provide recommended observational guidelines for using state-of-the-art and future ground-based radio observatories toward technosignature detection. Applying this framework, 16 exoplanet targets are proposed for radio observation. [ABSTRACT FROM AUTHOR]

The work in this paper aims at determining the evolution and possible co-evolution of radio-loud active galactic nuclei (AGNs) and their cores via their radio luminosity functions (i.e., total and core RLFs, respectively). Using a large combined sample of 1063 radio-loud AGNs selected at low radio frequency, we investigate the RLF at 408 MHz of steep-spectrum radio sources. Our results support a luminosity-dependent evolution. Using core flux density data of the complete sample 3CRR, we investigate the core RLF at 5.0 GHz. Based on the combined sample with incomplete core flux data, we also estimate the core RLF using a modified factor of completeness. Both results are consistent and show that the comoving number density of radio cores displays a persistent decline with redshift, implying a negative density evolution. We find that the core RLF is obviously different from the total RLF at the 408 MHz bands, which is mainly contributed by extended lobes, implying that the cores and extended lobes could not be co-evolving at radio emission. [ABSTRACT FROM AUTHOR]

Theoretical models and observations suggest that the abundances of molecular ions in protoplanetary disks should be highly sensitive to the variable ionization conditions set by the young central star. We present a search for temporal flux variability of HCO+ J = 1–0, which was observed as a part of the Molecules with Atacama Large Millimeter/submillimeter Array (ALMA) at Planet-forming Scales ALMA Large Program. We split out and imaged the line and continuum data for each individual day the five sources were observed (HD 163296, AS 209, GM Aur, MWC 480, and IM Lup, with between three and six unique visits per source). Significant enhancement (>3 σ) was not observed, but we find variations in the spectral profiles in all five disks. Variations in AS 209, GM Aur, and HD 163296 are tentatively attributed to variations in HCO+ flux, while variations in IM Lup and MWC 480 are most likely introduced by differences in the uv coverage, which impact the amount of recovered flux during imaging. The tentative detections and low degree of variability are consistent with expectations of X-ray flare-driven HCO+ variability, which requires relatively large flares to enhance the HCO+ rotational emission at significant (>20%) levels. These findings also demonstrate the need for dedicated monitoring campaigns with high signal-to-noise ratios to fully characterize X-ray flare-driven chemistry. [ABSTRACT FROM AUTHOR]

We study the evolution of a nonrelativistically expanding thin shell in radio-emitting tidal disruption events (TDEs) based on a one-dimensional spherically symmetric model considering the effect of both a time-dependent mass-loss rate of the disk wind and the ambient mass distribution. The analytical solutions are derived in two extreme limits; one is the approximate solution near the origin in the form of the Taylor series, and the other is the asymptotic solution in which the ambient matter is dominant far away from the origin. Our numerical solutions are confirmed to agree with the respective analytical solutions. We find that no simple power law of the time solution exists in early to middle times because the mass-loss rate varies over time, affecting the shell dynamics. We also discuss the application of our model to the observed radio-emitting TDE, AT 2019dsg. [ABSTRACT FROM AUTHOR]

Understanding dark matter is one of the most urgent questions in modern physics. A very interesting candidate is primordial black holes (PBHs). For the mass ranges <10−16 M ⊙ and >100 M ⊙, PBHs have been ruled out. However, they are still poorly constrained in the mass range 10−16–100 M ⊙. Fast radio bursts (FRBs) are millisecond flashes of radio light of unknown origin, mostly from outside the Milky Way. Due to their short timescales, gravitationally lensed FRBs, which are yet to be detected, have been proposed as a useful probe for constraining the presence of PBHs in the mass window of <100 M ⊙. Up to now, the most successful project in finding FRBs has been CHIME. Due to its large field of view, CHIME has detected at least 600 FRBs since 2018. However, none of them is confirmed to be gravitationally lensed. Taiwan plans to build a new telescope, the Bustling Universe Radio Survey Telescope in Taiwan (BURSTT), dedicated to detecting FRBs. Its survey area will be 25 times greater than CHIME. BURSTT can localize all of these FRBs through very long baseline interferometry. We estimate the probability to find gravitationally lensed FRBs, based on the scaled redshift distribution from the latest CHIME catalog and the lensing probability function from Munõz et al. BURSTT-2048 can detect ∼24 lensed FRBs out of ∼1700 FRBs per annum. With BURSTT's ability to detect nanosecond FRBs, we can constrain PBHs to form a part of dark matter down to 10−4 M ⊙. [ABSTRACT FROM AUTHOR]

Terahertz (THz) radiation encompasses a wide spectral range within the electromagnetic spectrum that extends from microwaves to the far infrared (100 GHz–∼30 THz). Within its frequency boundaries exist a broad variety of scientific disciplines that have presented, and continue to present, technical challenges to researchers. During the past 50 years, for instance, the demands of the scientific community have substantially evolved and with a need for advanced instrumentation to support radio astronomy, Earth observation, weather forecasting, security imaging, telecommunications, non-destructive device testing and much more. Furthermore, applications have required an emergence of technology from the laboratory environment to production-scale supply and in-the-field deployments ranging from harsh ground-based locations to deep space. In addressing these requirements, the research and development community has advanced related technology and bridged the transition between electronics and photonics that high frequency operation demands. The multidisciplinary nature of THz work was our stimulus for creating the 2017 THz Science and Technology Roadmap (Dhillon et al 2017 J. Phys. D: Appl. Phys. 50 043001). As one might envisage, though, there remains much to explore both scientifically and technically and the field has continued to develop and expand rapidly. It is timely, therefore, to revise our previous roadmap and in this 2023 version we both provide an update on key developments in established technical areas that have important scientific and public benefit, and highlight new and emerging areas that show particular promise. The developments that we describe thus span from fundamental scientific research, such as THz astronomy and the emergent area of THz quantum optics, to highly applied and commercially and societally impactful subjects that include 6G THz communications, medical imaging, and climate monitoring and prediction. Our Roadmap vision draws upon the expertise and perspective of multiple international specialists that together provide an overview of past developments and the likely challenges facing the field of THz science and technology in future decades. The document is written in a form that is accessible to policy makers who wish to gain an overview of the current state of the THz art, and for the non-specialist and curious who wish to understand available technology and challenges. A such, our experts deliver a 'snapshot' introduction to the current status of the field and provide suggestions for exciting future technical development directions. Ultimately, we intend the Roadmap to portray the advantages and benefits of the THz domain and to stimulate further exploration of the field in support of scientific research and commercial realisation. [ABSTRACT FROM AUTHOR]

We report the discovery and follow-up observations of VT 1137–0337, an unusual radio transient found in our systematic search for extragalactic explosions in the Very Large Array Sky Survey. It is located in the brightest region of a dwarf starburst galaxy at a luminosity distance of 121.6 Mpc. Its 3 GHz luminosity is comparable to luminous radio supernovae associated with dense circumstellar interaction and relativistic outflows. However, its broadband radio spectrum—proportional to ν −0.35 over a range of ≳10× in frequency and fading at a rate of 5% yr–1—cannot be directly explained by the shock of a stellar explosion. Jets launched by various classes of accreting black holes also struggle to account for VT 1137–0337's combination of observational properties. Instead, we propose that VT 1137–0337 is a decades-old pulsar wind nebula that has recently emerged from within the free–free opacity of its surrounding supernova ejecta. If the nebula is powered by spin-down, the central neutron star should have a surface dipole field of ∼1013–1014 G and a present-day spin period of ∼10–100 ms. Alternatively, the nebula may be powered by the release of magnetic energy from a magnetar. Magnetar nebulae have been proposed to explain the persistent radio sources associated with the repeating fast radio bursts FRB 121102 and FRB 190520B. These FRB persistent sources have not previously been observed as transients but do bear a striking resemblance to VT 1137–0337 in their radio luminosity, spectral index, and host galaxy properties. [ABSTRACT FROM AUTHOR]

The phenomenon of pulsar nulling, observed as the temporary inactivity of a pulsar, remains poorly understood both observationally and theoretically. Most observational studies that quantify nulling employ a variant of Ritchings algorithm, which can suffer significant biases for pulsars where the emission is weak. Using a more robust mixture model method, we study pulsar nulling in a sample of 22 recently discovered pulsars, for which we publish the nulling fractions for the first time. These data clearly demonstrate biases of the former approach and show how an otherwise nonnulling pulsar can be classified as having significant nulls. We show that the population-wide studies that find a positive correlation of nulling with pulsar period/characteristic age can similarly be biased because of the bias in estimating the nulling fraction. We use our probabilistic approach to find the evidence for periodicity in the nulls in a subset of three pulsars in our sample. In addition, we also provide improved timing parameters for 17 of the 22 pulsars that had no prior follow-up. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the spectral properties of 10 millisecond pulsars (MSPs) discovered by the uGMRT, observed from 2017 to 2023 using band 3 (300–500 MHz) and 4 (550–750 MHz) of the uGMRT. For these MSPs, we have reported a range of spectral indices from ∼0 to −4.8, while averaging the full observing band and all the observing epochs. For every MSP, we calculated the mean flux density across 7–8 subbands, each with approximately 25 MHz bandwidth spanning band 3 and band 4. We computed their modulation indices as well as average and maximum-to-median flux density within each subband. Using the temporal variations of the flux density we calculated the refractive scintillation timescales and estimated a structure function with a time lag for eight MSPs in the sample. We note a significant temporal evolution of the in-band spectra, classified into three categories based on the nature of the best-fit power-law spectra, having single positive spectral indices, multiple broken power laws, and single negative spectral indices. Additionally, indications of a low-frequency turnover and temporal variations of the turnover frequency (to the extent that turnover was observed for some of the epochs while not seen for the rest) were noted for all the MSPs. To the best of our knowledge, this is the first systematic investigation probing temporal changes in MSP spectra as well as in the turnover frequency. Future exploration with dense monitoring combined with the modeling of spectra can provide vital insight into the intrinsic emission properties of MSPs and interstellar medium properties.

In 2021, a catalog of 536 fast radio bursts (FRBs) detected with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) radio telescope was released by the CHIME/FRB Collaboration. This large collection of bursts, observed with a single instrument and uniform selection effects, has advanced our understanding of the FRB population. Here we update the results for 140 of these FRBs for which channelized raw voltage (“baseband”) data are available. With the voltages measured by the telescope’s antennas, it is possible to maximize the telescope sensitivity in any direction within the primary beam, an operation called “beamforming.” This allows us to increase the signal-to-noise ratios of the bursts and to localize them to subarcminute precision. The improved localizations are also used to correct the beam response of the instrument and to measure fluxes and fluences with an ∼10% uncertainty. Additionally, the time resolution is increased by 3 orders of magnitude relative to that in the first CHIME/FRB catalog, and, applying coherent dedispersion, burst morphologies can be studied in detail. Polarization information is also available for the full sample of 140 FRBs, providing an unprecedented data set to study the polarization properties of the population. We release the baseband data beamformed to the most probable position of each FRB. These data are analyzed in detail in a series of accompanying papers.

The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies. Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy’s observed luminosity. Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars. The collective bound implies fewer than $\sim {10}^{6}{(\bar{{\ell }}/{10}^{13}\ {\rm{W}})}^{-1}$ L -band broadcasts per star per gigahertz in the Milky Way wideband and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.

NICER has observed a few millisecond pulsars where the geometry of the X-ray-emitting hotspots on the neutron star have been analyzed in order to constrain the mass and radius from X-ray light-curve modeling. One example, PSR J0030 + 0451, has been shown to possibly have significant multipolar magnetic fields at the stellar surface. Using force-free simulations of the magnetosphere structure, it has been shown that the radio, X-ray, and γ -ray light curves can be modeled simultaneously with an appropriate field configuration. An even more stringent test is to compare predictions of the force-free magnetosphere model with observations of radio polarization. This paper attempts to reproduce the radio polarization of PSR J0030 + 0451 using a force-free magnetospheric solution. As a result of our modeling, we can reproduce certain features of the polarization well.

The Event Horizon Telescope (EHT) is an earth-size aperture synthesis radio astronomy array capable of making high-resolution measurements of submillimeter emission near the event horizon of supermassive black holes. The EHT uses existing standalone submillimeter radio telescopes which are retrofitted to serve as VLBI stations. Current instrument development goals include increasing the number of stations in the array and increasing their sensitivity. We have developed a 4 GHz bandwidth digital backend (DBE) unit, based on the CASPER (Collaboration for Astronomy Signal Processing and Electronics Research) open source ROACH2 (Reconfigurable Open Architecture Computing Hardware) platform. The ROACH2 digital backend, which we call the, R2DBE has dual channels each sampling at a rate of 4096 MSps (megasamples-per-second), a factor of 4 improvement over the previous generation system. Recording 2-bits per sample, the bandwidth is equivalently stated as 16 gigabits-per-second (Gbps). This paper includes system design of the R2DBE, discusses laboratory test results of the system using correlated noise input, and presents field test results. The R2DBE was distributed to seven sites in early 2015, enabling the EHT campaign in 2015March to collect data with 2 GHz bandwidth in each polarization. The 16 gigabit-per-second (Gbps) R2DBE can be scaled to create a 64 Gbps system using four R2DBEs in parallel. Thus, it enables a clear path to the EHT's goal of 4 GHz dual-polarization and dual-sideband across the array. [ABSTRACT FROM AUTHOR]

Pulsar timing arrays (PTAs) are galactic-scale gravitational wave (GW) detectors. Each individual arm, composed of a millisecond pulsar, a radio telescope, and a kiloparsecs-long path, differs in its properties but, in aggregate, can be used to extract low-frequency GW signals. We present a noise and sensitivity analysis to accompany the NANOGrav 15 yr data release and associated papers, along with an in-depth introduction to PTA noise models. As a first step in our analysis, we characterize each individual pulsar data set with three types of white-noise parameters and two red-noise parameters. These parameters, along with the timing model and, particularly, a piecewise-constant model for the time-variable dispersion measure, determine the sensitivity curve over the low-frequency GW band we are searching. We tabulate information for all of the pulsars in this data release and present some representative sensitivity curves. We then combine the individual pulsar sensitivities using a signal-to-noise ratio statistic to calculate the global sensitivity of the PTA to a stochastic background of GWs, obtaining a minimum noise characteristic strain of 7 × 10 ^−15 at 5 nHz. A power-law-integrated analysis shows rough agreement with the amplitudes recovered in NANOGrav’s 15 yr GW background analysis. While our phenomenological noise model does not model all known physical effects explicitly, it provides an accurate characterization of the noise in the data while preserving sensitivity to multiple classes of GW signals.

“TRAO FUNS” is a project to survey the Gould Belt’s clouds in molecular lines. This paper presents its first results on the central region of the California molecular cloud, L1478. We performed on-the-fly mapping observations using the Taeduk Radio Astronomy Observatory 14 m single-dish telescope equipped with a 16 multibeam array covering a ∼1.0 square degree area of this region using , mainly tracing low-density clouds, and a ∼460 square arcminute area using , mainly tracing dense cores. and were also used simultaneously to map a ∼440 square arcminute area of this region. We identified 10 filaments by applying the dendrogram technique to the data cube and 8 dense cores using FellWalker. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that L1478 consists of several filaments with slightly different velocities. Particularly, the filaments that are supercritical are found to contain dense cores detected in . A comparison of nonthermal velocity dispersions derived from and for the filaments and dense cores indicates that some of the dense cores share kinematics similar to those of the surrounding filaments, while several dense cores have different kinematics from those of their filaments. This suggests that the formation mechanism of dense cores and filaments can be different in individual filaments depending on their morphologies and environments. [ABSTRACT FROM AUTHOR]

A measurement of the cosmological signal remains a promising but as-of-yet unattained ambition of radio astronomy. A positive detection would provide direct observations of key unexplored epochs of our cosmic history, including the cosmic dark ages and reionization. In this paper, we concentrate on measurements of the spatial monopole of the brightness temperature as a function of redshift (the “global signal”). Most global experiments to date have been single-element experiments. In this paper, we show how an interferometer can be designed to be sensitive to the monopole mode of the sky, thus providing an alternate approach to accessing the global signature. We provide simple rules of thumb for designing a global signal interferometer and use numerical simulations to show that a modest array of tightly packed antenna elements with moderately sized primary beams (FWHM of ) can compete with typical single-element experiments in their ability to constrain phenomenological parameters pertaining to reionization and the pre-reionization era. We also provide a general data analysis framework for extracting the global signal from interferometric measurements (with analysis of single-element experiments arising as a special case) and discuss trade-offs with various data analysis choices. Given that interferometric measurements are able to avoid a number of systematics inherent in single-element experiments, our results suggest that interferometry ought to be explored as a complementary way to probe the global signal. [ABSTRACT FROM AUTHOR]

LIGO, the Laser Interferometer Gravitational-wave Observatory, has been designed and constructed to measure gravitational wave strain via differential arm length. The LIGO 4 km Michelson arms with Fabry–Perot cavities have auxiliary length control servos for suppressing Michelson motion of the beam-splitter and arm cavity input mirrors, which degrades interferometer sensitivity. We demonstrate how a post facto pipeline improves a data sample from LIGO Science Run 6 with feedforward subtraction. Dividing data into 1024 s windows, we numerically fit filter functions representing the frequency-domain transfer functions from Michelson length channels into the gravitational-wave strain data channel for each window, then subtract the filtered Michelson channel noise (witness) from the strain channel (target). In this paper we describe the algorithm, assess achievable improvements in sensitivity to astrophysical sources, and consider relevance to future interferometry. [ABSTRACT FROM AUTHOR]

We present the power spectrum methodology used for the first-season COMAP analysis, and assess the quality of the current data set. The main results are derived through the Feedâ€"Feed Pseudo-Cross-Spectrum (FPXS) method, which is a robust estimator with respect to both noise modeling errors and experimental systematics. We use effective transfer functions to take into account the effects of instrumental beam smoothing and various filter operations applied during the low-level data processing. The power spectra estimated in this way have allowed us to identify a systematic error associated with one of our two scanning strategies, believed to be due to residual ground or atmospheric contamination. We omit these data from our analysis and no longer use this scanning technique for observations. We present the power spectra from our first season of observing, and demonstrate that the uncertainties are integrating as expected for uncorrelated noise, with any residual systematics suppressed to a level below the noise. Using the FPXS method, and combining data on scales k = 0.051â€"0.62 Mpcâˆ'1, we estimate P CO(k) = âˆ'2. 7 ± 1.7 Ă— 104 ÎĽ K2 Mpc3, the first direct 3D constraint on the clustering component of the CO(1â€"0) power spectrum in the literature. [ABSTRACT FROM AUTHOR]

We study the impact of primordial magnetic fields on the H I absorption from the epoch of reionization. The presence of these fields results in two distinct effects: (1) the heating of the halos from the decay of the magnetic fields owing to ambipolar diffusion, and (2) an increase in the number of halos owing to additional matter fluctuations induced by magnetic fields. We analyze both of these effects and show that the latter is potentially observable because the number of halos along of line of sight can increase by many orders of magnitude. While this effect is not strongly dependent on the magnetic field strength in the range 0.3-0.6 nG, it is extremely sensitive to the magnetic field power spectral index for the near scale-free models. Therefore, the detection of such absorption features could be a sensitive probe of the primordial magnetic field and its power spectrum. We discuss the detectability of these features with the ongoing and future radio interferometers. In particular, we show that LOFAR might be able to detect these absorption features at z ≃ 10 in less than 10 hr of integration if the flux of the background source is 400 mJy. [ABSTRACT FROM AUTHOR]

Neutral gas is commonly believed to dominate over stars in the outskirts of galaxies, and investigations of the disk-halo interface are generally considered to be in the domain of radio astronomy. This may simply be a consequence of the fact that deep H i observations typically probe to a lower-mass surface density than visible wavelength data. This paper presents low-surface-brightness, optimized visible wavelength observations of the extreme outskirts of the nearby spiral galaxy NGC 2841. We report the discovery of an enormous low-surface brightness stellar disk in this object. When azimuthally averaged, the stellar disk can be traced out to a radius of ∼70 kpc (5 R25 or 23 inner disk scale lengths). The structure in the stellar disk traces the morphology of H i emission and extended UV emission. Contrary to expectations, the stellar mass surface density does not fall below that of the gas mass surface density at any radius. In fact, at all radii greater than ∼20 kpc, the ratio of the stellar mass to gas mass surface density is a constant 3:1. Beyond ∼30 kpc, the low-surface-brightness stellar disk begins to warp, which may be an indication of a physical connection between the outskirts of the galaxy and infall from the circumgalactic medium. A combination of stellar migration, accretion, and in situ star formation might be responsible for building up the outer stellar disk, but whatever mechanisms formed the outer disk must also explain the constant ratio between stellar and gas mass in the outskirts of this galaxy. [ABSTRACT FROM AUTHOR]

Understanding how material accretes onto the rotationally supported disk from the surrounding envelope of gas and dust in the youngest protostellar systems is important for describing how disks are formed. Magnetohydrodynamic simulations of magnetized, turbulent disk formation usually show spiral-like streams of material (accretion flows) connecting the envelope to the disk. However, accretion flows in these early stages of protostellar formation still remain poorly characterized, due to their low intensity, and possibly some extended structures are disregarded as being part of the outflow cavity. We use ALMA archival data of a young Class 0 protostar, Lupus 3-MMS, to uncover four extended accretion flowâ€"like structures in C18O that follow the edges of the outflows. We make various types of positionâ€"velocity cuts to compare with the outflows and find the extended structures are not consistent with the outflow emission, but rather more consistent with a simple infall model. We then use a dendrogram algorithm to isolate five substructures in positionâ€"positionâ€"velocity space. Four out of the five substructures fit well (>95%) with our simple infall model, with specific angular momenta between 2.7â€"6.9 Ă— 10âˆ'4 km sâˆ'1 pc and mass-infall rates of 0.5â€"1.1 Ă— 10âˆ'6 M ⊙ yrâˆ'1. Better characterization of the physical structure in the supposed “outflow cavities” is important to disentangle the true outflow cavities and accretion flows. [ABSTRACT FROM AUTHOR]

A stable-frequency transmitter with relative radial acceleration to a receiver will show a change in received frequency over time, known as a “drift rate.” For a transmission from an exoplanet, we must account for multiple components of drift rate: the exoplanet’s orbit and rotation, the Earth’s orbit and rotation, and other contributions. Understanding the drift rate distribution produced by exoplanets relative to Earth, can (a) help us constrain the range of drift rates to check in a Search for Extraterrestrial Intelligence project to detect radio technosignatures, and (b) help us decide validity of signals-of-interest, as we can compare drifting signals with expected drift rates from the target star. In this paper, we modeled the drift rate distribution for ∼5300 confirmed exoplanets, using parameters from the NASA Exoplanet Archive (NEA). We find that confirmed exoplanets have drift rates such that 99% of them fall within the ±53 nHz range. This implies a distribution-informed maximum drift rate ∼4 times lower than previous work. To mitigate the observational biases inherent in the NEA, we also simulated an exoplanet population built to reduce these biases. The results suggest that, for a Kepler-like target star without known exoplanets, ±0.44 nHz would be sufficient to account for 99% of signals. This reduction in recommended maximum drift rate is partially due to inclination effects and bias toward short orbital periods in the NEA. These narrowed drift rate maxima will increase the efficiency of searches and save significant computational effort in future radio technosignature searches.

The search for extraterrestrial intelligence (SETI) commensal surveys aim to scan the sky to find possible technosignatures from an extraterrestrial intelligence (ETI). The mitigation of radio frequency interference (RFI) is an important step, especially for the most sensitive Five-hundred-meter Aperture Spherical radio Telescope (FAST), which can detect more weak RFI. In this paper, we propose several new techniques for RFI mitigation and use our procedure to search for ETI signals from the archival data of FAST’s first SETI commensal survey. We detect the persistent narrowband RFI by setting a threshold of the signals’ sky separation and detect the drifting RFI (and potentially other types of RFI) using the Hough transform. We also use the clustering algorithms to remove more RFI and select candidates. The results of our procedure are compared to the earlier work on the same FAST data. We find that our methods, though relatively simpler in computation, remove more RFI (99.9912% compared to 99.9063% in the earlier work) but preserve the simulated ETI signals, except for those (5.1%) severely affected by the RFI. We also report more interesting candidate signals, about a dozen of which are new candidates that were not previously reported. In addition, we find that the proposed Hough transform method, with suitable parameters, also has the potential to remove the broadband RFI. We conclude that our methods can effectively remove the vast majority of the RFI while preserving and finding the candidate signals that we are interested in.

Fast radio bursts (FRBs) are bright radio transients of microsecond to millisecond duration and unknown extragalactic origin. Central to the mystery of FRBs are their extremely high characteristic energies, which surpass the typical energies of other radio transients of similar duration, like Galactic pulsar and magnetar bursts, by orders of magnitude. Calibration of FRB-detecting telescopes for burst flux and fluence determination is crucial for FRB science, as these measurements enable studies of the FRB energy and brightness distribution in comparison to progenitor theories. The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a radio interferometer of cylindrical design. This design leads to a high FRB detection rate but also leads to challenges for CHIME/FRB flux calibration. This paper presents a comprehensive review of these challenges, as well as the automated flux calibration software pipeline that was developed to calibrate bursts detected in the first CHIME/FRB catalog, consisting of 536 events detected between 2018 July 25 and 2019 July 1. We emphasize that, due to limitations in the localization of CHIME/FRB bursts, flux and fluence measurements produced by this pipeline are best interpreted as lower limits, with uncertainties on the limiting value.

This paper presents an observation of quasi-periodic rapidly propagating waves observed in the Atmospheric Image Assembly (AIA) 171/193 Å channels during the impulsive phase of an M1.9 flare that occurred on 2012 May 7. The instant period was found to decrease from 240 to 120 s, and the speed of the wavefronts was in the range of ∼664–1416 km s−1. Almost simultaneously, quasi-periodic bursts with similar instant periods, ∼70 and ∼140 s, occur in the microwave emission and in decimetric type IV and type III radio bursts, and in the soft X-ray emission. The magnetic field configuration of the flare site was consistent with a breakout topology, i.e., a quadrupolar field along with a magnetic null point. The quasi-periodic rapidly propagating wavefronts of the EUV emission are interpreted as a fast magnetoacoustic wave train. The observations suggest that the fast-mode waves are generated during the quasi-periodic magnetic reconnection in the cusp region above the flare arcade loops. For the first time, we provide evidence of a tadpole wavelet signature at about 70–140 s in decimetric (245/610 MHz) radio bursts, along with the direct observation of a coronal fast-mode wave train in EUV. In addition, at AIA 131/193 Å we observed quasi-periodic EUV disturbances with periods of 95 and 240 s propagating downward at apparent speeds of 172–273 km s−1. The nature of these downward propagating disturbances is not revealed, but they could be connected to magnetoacoustic waves or periodically shrinking loops. [ABSTRACT FROM AUTHOR]

We present the results on the physical properties of filaments and dense cores in IC 5146, as a part of the TRAO FUNS project. We carried out on-the-fly mapping observations using the Taeduk Radio Astronomy Observatory (TRAO) 14 m telescope covering about 1 square degree of the area of IC 5146 using various molecular lines. We identified 14 filaments (24 in total, including sub-filaments) from the C18O (1–0) data cube and 22 dense cores from the N2H+ (1–0) data. We examined the filaments' gravitational criticality, turbulence properties, accretion rate from filaments to dense cores, and relative evolutionary stages of cores. Most filaments in IC 5146 are gravitationally supercritical within the uncertainty, and most dense cores are formed in them. We found that dense cores in the hubs show a systemic velocity shift of ∼0.3 km s−1 between the N2H+ and C18O gas. Besides, these cores are subsonic or transonic, while the surrounding filament gas is transonic or supersonic, indicating that the cores in the hubs are likely formed by the dissipation of turbulence in the colliding turbulent filaments and the merging is still ongoing. We estimated a mass accretion rate of 15–35 M⊙ Myr−1 from the filaments to the dense cores, and the required timescales to collect the current core mass are consistent with the lifetime of the dense cores. The structures of filaments and dense cores in the hub can form from a collision of turbulent converging flows, and mass flow along the filaments to the dense cores may play an important role in forming dense cores. [ABSTRACT FROM AUTHOR]

This paper presents multiwavelength observations of a flare-generated type II radio burst. The kinematics of the shock derived from the type II burst closely match a fast extreme ultraviolet (EUV) wave seen propagating through coronal arcade loops. The EUV wave was closely associated with an impulsive M1.0 flare without a related coronal mass ejection, and was triggered at one of the footpoints of the arcade loops in active region NOAA 12035. It was initially observed in the 335 Å images from the Atmospheric Image Assembly with a speed of ∼800 km s−1 and it accelerated to ∼1490 km s−1 after passing through the arcade loops. A fan–spine magnetic topology was revealed at the flare site. A small, confined filament eruption (∼340 km s−1) was also observed moving in the opposite direction to the EUV wave. We suggest that breakout reconnection in the fan–spine topology triggered the flare and associated EUV wave that propagated as a fast shock through the arcade loops. [ABSTRACT FROM AUTHOR]

We test a new technique for studying magnetohydrodynamic turbulence suggested by Lazarian & Pogosyan, using synthetic observations of synchrotron polarization. This paper focuses on a one-point statistics, which is termed polarization frequency analysis, that is characterized by the variance of polarized emission as a function of the square of the wavelength along a single line of sight. We adopt the ratio η of the standard deviation of the line-of-sight turbulent magnetic field to the line-of-sight mean magnetic field to depict the level of turbulence. When this ratio is large (), which characterizes a region dominated by turbulent field, or small (), which characterizes a region dominated by the mean field, we obtain the polarization variance or , respectively. At small η, i.e., in the region dominated by the mean field, we successfully recover the turbulent spectral index from the polarization variance. We find that our simulations agree well with the theoretical prediction of Lazarian & Pogosyan. With existing and upcoming data cubes from the Low-Frequency Array for Radio Astronomy (LOFAR) and the Square Kilometer Array (SKA), this new technique can be applied to study the magnetic turbulence in the Milky Way and other galaxies. [ABSTRACT FROM AUTHOR]

While observations of many high-precision radio pulsars of order ≲1 μs across the sky are needed for the detection and characterization of a stochastic background of low-frequency gravitational waves (GWs), sensitivity to single sources of GWs requires even higher timing precision. The Argentine Institute of Radio Astronomy (IAR; Instituto Argentino de Radioastronomía) has begun observations of the brightest known millisecond pulsar, J0437−4715. Even though the two antennas are smaller than other single-dish telescopes previously used for pulsar timing array (PTA) science, the IAR's capability to monitor this pulsar daily, coupled with the pulsar's brightness, allows for high-precision measurements of pulse-arrival time. While upgrades of the facility are currently underway, we show that modest improvements beyond current plans will provide IAR with unparalleled sensitivity to this pulsar. The most stringent upper limits on single GW sources come from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). Observations of PSR J0437−4715 will provide a significant sensitivity increase in NANOGrav's "blind spot" in the sky where fewer pulsars are currently being observed. With state-of-the-art instrumentation installed, we estimate the array's sensitivity will improve by a factor of ≈2–4 over 10 yr for 20% of the sky with the inclusion of this pulsar, as compared to a static version of the PTA used in NANOGrav's most recent limits. More modest instrumentation results in factors of ≈1.4–3. We identify four other candidate pulsars as suitable for inclusion in PTA efforts. International PTA efforts will also benefit from inclusion of these data, given the potential achievable sensitivity. [ABSTRACT FROM AUTHOR]

Closure phases and closure amplitudes have proven critical to modern radio interferometry due to their insensitivity to the uncertain station gains. We present the first set of closure quantities constructed from parallel-hand and cross-hand visibilities that are insensitive to both station gains and to polarimetric leakage. These complex "closure traces" are a natural extension of closure amplitudes and closure phases, are independent of all station-based linear corruptions of the polarized visibilities, and are complete in the sense that they contain all remaining information present in the visibility data. Products of closure traces on so-called "conjugate" quadrangles are sensitive only to structure in the source polarization fraction—independent of variations in the Stokes I structure—and thereby provide unambiguous probes of polarization in astronomical sources. [ABSTRACT FROM AUTHOR]

Type II radio bursts are thought to be a signature of coronal shocks. In this paper, we analyze a short-lived type II burst that started at 07:40 UT on 2011 February 28. By carefully checking white-light images, we find that the type II radio burst is not accompanied by a coronal mass ejection, only by a C2.4 class flare and narrow jet. However, in the EUV images provided by the Atmospheric Imaging Assembly on board the Solar DynamicsObservatory, we find a wave-like structure that propagated at a speed of ∼600 km s−1 during the burst. The relationship between the type II radio burst and the wave-like structure is, in particular, explored. For this purpose, we first derive the density distribution under the wave by the differential emission measure method, which is used to restrict the empirical density model. We then use the restricted density model to invert the speed of the shock that produces the observed frequency drift rate in the dynamic spectrum. The inverted shock speed is similar to the speed of the wave-like structure. This implies that the wave-like structure is most likely a coronal shock that produces the type II radio burst. We also examine the evolution of the magnetic field in the flare-associated active region and find continuous flux emergence and cancellation taking place near the flare site. Based on these facts, we propose a new mechanism for the formation of the type II radio burst, i.e., the expansion of the strongly inclined magnetic loops after reconnecting with a nearby emerging flux acts as a piston to generate the shock wave. [ABSTRACT FROM AUTHOR]

A global understanding of active galactic nuclei (AGN) and their host galaxies hinges on completing a census of AGN activity without selection biases down to the low-luminosity regime. Toward that goal, we identify AGN within faint radio populations at cosmic noon selected from new ultradeep, high-resolution imaging from the Karl G. Jansky Very Large Array at 6 and 3 GHz. These radio data are spatially coincident with the ultradeep legacy surveys in the GOODS-S/HUDF region, particularly the unparalleled Chandra 7 Ms X-ray imaging. Combined, these data sets provide a unique basis for a thorough census of AGN, allowing simultaneous identification via (1) high X-ray luminosity, (2) hard X-ray spectra, (3) excess X-ray relative to 6 GHz, (4) mid-IR colors, (5) SED fitting, (6) radio excess via the radio–infrared relation, (7) flat radio spectra via multiband radio, and (8) optical spectroscopy. We uncover AGN in fully half our faint radio sample, indicating a source density of one AGN arcmin−2, with a similar number of radio-undetected AGN identified via X-ray over the same area. Our radio-detected AGN are majority radio-quiet, with radio emission consistent with being powered predominantly by star formation. Nevertheless, we find AGN radio signatures in our sample: ∼12% with radio excess indicating radio-loud activity, and ∼16% of radio-quiet AGN candidates with flat or inverted radio spectra. The latter is a lower limit, pending our upcoming deeper 3 GHz survey. Finally, despite these extensive data sets, this work is likely still missing heavily obscured AGN. We discuss in detail this elusive population and the prospects for completing our AGN census with James Webb Space Telescope/MIRI. [ABSTRACT FROM AUTHOR]