Radio Astronomy Observatory Research Articles

A technique to detect periodic and non-periodic ultra-rapid flux time variations with standard radio-astronomical data

We demonstrate that extremely rapid and weak periodic and non-periodic signals can easily be detected by using the autocorrelation of intensity as a function of time. We use standard radio-astronomical observations that have artificial periodic and non-periodic signals generated by the electronics of terrestrial origin. The autocorrelation detects weak signals that have small amplitudes because it averages over long integration times. Another advantage is that it allows a direct visualization of the shape of the signals, while it is difficult to see the shape with a Fourier transform. Although Fourier transforms can also detect periodic signals, a novelty of this work is that we demonstrate another major advantage of the autocorrelation, that it can detect non-periodic signals while the Fourier transform cannot. Another major novelty of our work is that we use electric fields taken in a standard format with standard instrumentation at a radio observatory and therefore no specialized instrumentation is needed. Because the electric fields are sampled every 15.625 nanoseconds, they therefore allow detection of very rapid time variations. Notwithstanding the long integration times, the autocorrelation detects very rapid intensity variations as a function of time. The autocorrelation could also detect messages from Extraterrestrial Intelligence as non-periodic signals.

Coronal Mass Ejections in September 2017 from Monitoring of Interplanetary Scintillations with the Large Phased Array of the Lebedev Institute of Physics

Results of monitoring of interplanetary scintillations with the Large Phased Array of the Pushchino Radio AstronomyObservatory at 111 MHz during a period of flare activity of the Sun in the first ten days of September 2017 are presented. Enhancements of scintillations associated with interplanetary coronal mass ejections propagating after limb flares have been recorded. The propagation velocities are estimated to be about 2000 km/s for an ejection on September 7 and about 1000 km/s for an ejection on September 6. It is shown that, during the propagation from the Sun, the lateral part of the ejections decelerates faster than its leading part. Night-time enhancements of second-timescale scintillations during periods of high geomagnetic activity have an ionospheric origin.

A masing event in NGC 6334I: contemporaneous flaring of hydroxyl, methanol, and water masers

As a product of the maser monitoring program with the 26m telescope of the Hartebeesthoek Radio Astronomy Observatory (HartRAO), we present an unprecedented, contemporaneous flaring event of 10 maser transitions in hydroxyl, methanol, and water that began in 2015 January in the massive star-forming region NGC6334I in the velocity range -10 to -2 km/s. The 6.7 GHz methanol and 22.2 GHz water masers began flaring within 22 days of each other, while the 12.2 GHz methanol and 1665 MHz hydroxyl masers flared 80 and 113 days later respectively. The 1665 MHz, 6.7 GHz, and 22.2 GHz masers have all remained in their flared state for nearly 3 years. The brightest flaring components increased by factors of 66, 21, 26, and 20 in the 12.2 and 6.7 GHz methanol, 1665 MHz hydroxyl and 22.2 GHz water maser transitions respectively; some weaker components increased by up to a factor of 145. We also report new maser emission in the 1720, 6031, and 6035 MHz OH lines and the 23.1 GHz methanol line, along with the detection of only the fifth 4660 MHz OH maser. We note the correlation of this event with the extraordinary (sub)millimeter continuum outburst from the massive protostellar system NGC6334I-MM1 and discuss the implications of the observed time lags between different maser velocity components on the nature of the outburst. Finally, we identify two earlier epoch maser flaring events likely associated with this object, which suggest a recurring accretive phenomenon that generates powerful radiative outbursts.

Russian-Cuban Colocation Station for Radio Astronomical Observation and Monitoring of Near-Earth Space

The article presents the main possibilities of using the projected Russian-Cuban geodynamic colocation station on the basis of the Institute of Geophysics and Astronomy of the Ministry of Science, Technology and the Environment of the Republic of Cuba to carry out radio observations and monitoring the near-Earth space. Potential capabilities of the station are considered for providing various observational programs: astrophysical observations; observations by space geodesy methods using radio very long baselines interferometers, global navigation satellite systems, laser rangers, and various Doppler systems, as well as monitoring of artificial and natural bodies in the near-Earth and deep space, including the ranging of asteroids approaching the Earth. The results of modeling the observations on the planned station are compared with that obtained on the existing geodynamic stations. The efficiency of the projected Russian-Cuban station for solving astronomical tasks is considered.

A twofold mission to the moon: Objectives and payloads

Ukraine has scientific and technical potential to construct a spacecraft and payloads for exploration of the Moon in collaboration with other interested countries. In this paper we propose a double mission that consists of two parts: (1) orbiter exploration from an elongated orbit with a pericenter over the north pole (100 km above the surface) and the apocenter over the south pole (altitude about 3000 km), and (2) exploration with a lander located on the lunar farside near the south pole in the surroundings of the crater Braude. The lander carries five antennas for radio astronomy observations from hundreds of KHz to 40 MHz. The farside landing is necessary to provide effective shielding electromagnetic noises from the Earth, including aurora and lighting radiation. The lander communicates with the relay satellite in a high portion of the orbit; the orbiter is equipped with scientific payloads for investigation of the lunar surface. In the mode of a radio spectrometer, the radio antennas may study solar flares of various types, coronal mass ejections, Jupiter radio emission (L and S bursts), and Saturn (lightning and kilometer radio emission). Overlapping frequencies in the range of 10–40 MHz will allow coordination with terrestrial radio telescopes of IRA NAS, Ukraine (UTR-2, GURT), whose operation is limited by the Earth ionosphere. The absence of terrestrial noise allows us to approach the solution of the problem of searching for cosmological effects associated with the line of neutral hydrogen at Z = 50 … 100. The lander panoramic camera equipped with color and polarization filters provides important observations of horizon glow caused by the effect of electrostatic levitation of the lunar dust. For the orbital module we suggest remote-sensing instruments, which had not previously been used in space exploration of the Moon. The expected spatial resolution of the data will be about 100 m for the northern hemisphere. The equipment should include instruments, prototypes of which are already available in science organizations of Ukraine. These include an infrared spectrometer to map the abundance of OH/H2O compounds in the lunar soil. A HiRes camera operating in two spectral bands is suggested for mapping structural and mineralogical characteristics of young surface formations. The 3-mm radar, working in a squint mode, will not only map the radio brightness of the surface, which characterizes its roughness, but also improve the lunar topographic model with a spatial resolution of 100 m.

Subarray Processing for Projection-based RFI Mitigation in Radio Astronomical Interferometers

Abstract Radio Frequency Interference (RFI) is a major problem for observations in Radio Astronomy (RA). Adaptive spatial filtering techniques such as subspace projection are promising candidates for RFI mitigation; however, for radio interferometric imaging arrays, these have primarily been used in engineering demonstration experiments rather than mainstream scientific observations. This paper considers one reason that adoption of such algorithms is limited: RFI decorrelates across the interferometric array because of long baseline lengths. This occurs when the relative RFI time delay along a baseline is large compared to the frequency channel inverse bandwidth used in the processing chain. Maximum achievable excision of the RFI is limited by covariance matrix estimation error when identifying interference subspace parameters, and decorrelation of the RFI introduces errors that corrupt the subspace estimate, rendering subspace projection ineffective over the entire array. In this work, we present an algorithm that overcomes this challenge of decorrelation by applying subspace projection via subarray processing (SP-SAP). Each subarray is designed to have a set of elements with high mutual correlation in the interferer for better estimation of subspace parameters. In an RFI simulation scenario for the proposed ngVLA interferometric imaging array with 15 kHz channel bandwidth for correlator processing, we show that compared to the former approach of applying subspace projection on the full array, SP-SAP improves mitigation of the RFI on the order of 9 dB. An example of improved image synthesis and reduced RFI artifacts for a simulated image “phantom” using the SP-SAP algorithm is presented.

Superflares of H2O Maser Emission Toward the Protostellar Object G25.65+1.05 (IRAS 18316−0602)

The results of the study of the maser emission source IRAS 18316$-$0602 in the H$_2$O line at $\lambda =1.35$ cm are reported. The observations have been carried out at the RT-22 radio telescope of the Pushchino Radio Astronomy Observatory (Russia) since June 2002 until March 2017. Three superflares have been detected, in 2002, 2010, and 2016, with peak flux densities of 3400, 19,000, and 46,000 Jy, respectively. The results of the analysis of the superflares are given. The flares took place during periods of high maser activity in a narrow interval of radial velocities (40.5-42.5 km/s) and could be associated with the passage of a strong shock wave. During our monitoring the emission of three groups of features at radial velocities of about 41, 42, and 43 km/s dominated. The flare of 2016 was accompanied by a considerable increase in the flux densities of several features in an interval of 35--56 km/s.

Flares of the H2O Maser Emission in the Young Stellar Object GH2O 092.67+03.07 (IRAS 21078+5211)

The results of monitoring the H2O maser observed toward the region GH2O 092.67+03.07 (IRAS 21078+5211) located in the Giant Molecular Cloud Cygnus OB7 are presented. The observations were carried out with the 22-m radio telescope of the Pushchino Radio Astronomy Observatory in 2006–2017. Strong flares of the H2O maser emission with flux densities up to 19 800 Jy were detected. The flares exhibited both global (over the source) and local characters. All the flares were accompanied by strong variations in the H2O spectra within the corresponding radial-velocity ranges. Individual H2O components form both compact clusters and chains 1–2-AU long. Analysis of the variations of the fluxes, radial velocities, and line shapes of features during the flares showed that the medium may be strongly fragmented, with small-scale turbulent motions taking place in the H2Omaser region.

Multi-criteria decision analysis integrated with GIS for radio astronomical observatory site selection in peninsular of Malaysia

The purpose of this article is to choose the best possible places for radio astronomical observations sites using Multi-Criteria Decision Analysis (MCDA) coordinatedusing Geographical Information Systems (GIS). The study was carried out in the Peninsular of Malaysia, which is favourable for astronomical site observatory facilities with its appropriate climate properties and weather environments. Eleven factors were resolved, divided into two categories; geographical and anthropogenic. This parameter was estimated using Analytical Hierarchy Process technique and the weights of criteria layers were determined. Therefore, the most suitable areas were located widely in eastern and southern part of Peninsular Malaysia. This finding offers a sturdy, accurate, cost and time effective procedure for preliminary site selection for radio astronomical observatory.

Radio telescope spots aromatic molecule for first time

Astronomers have identified an aromatic molecule in space using a radio telescope for the first time, spotting benzonitrile in an interstellar dust cloud 430 light-years away. Brett A. McGuire, a Hubble fellow at the National Radio Astronomy Observatory, and colleagues plan to use the spectroscopic data they collected to figure out how this and other complex chemicals arise in outer space (Science 2018, DOI: 10.1126/science.aao4890). Astrochemists have known that polycyclic aromatic hydrocarbons (PAHs) make up an estimated 10% of all interstellar carbon in the universe, but it has been challenging for them to distinguish one PAH from another. Bond-stretching motions in the molecules’ infrared spectra are too similar to parse, and many PAHs lack strong polarity, making signatures in their rotational spectra—typically collected with radio telescopes—difficult to detect. Although benzonitrile isn’t strictly a PAH because of the nitrogen it contains, McGuire’s group set its sights on the molecule because of

A digital correlator upgrade for the Arcminute MicroKelvin Imager

The Arcminute Microkelvin Imager (AMI) telescopes located at the Mullard Radio Astronomy Observatory near Cambridge have been significantly enhanced by the implementation of a new digital correlator with 1.2 MHz spectral resolution. This system has replaced a 750-MHz resolution analogue lag-based correlator, and was designed to mitigate the effects of radio frequency interference, particularly from geostationary satellites that contaminate observations at low declinations. The upgraded instrument consists of 18 ROACH2 Field Programmable Gate Array platforms used to implement a pair of real-time FX correlators -- one for each of AMI's two arrays. The new system separates the down-converted RF baseband signal from each AMI receiver into two 2.3 GHz-wide sub-bands which are each digitized at 5-Gsps with 8 bits of precision. These digital data streams are filtered into 2048 frequency channels and cross-correlated using FPGA hardware, with a commercial 10 Gb Ethernet switch providing high-speed data interconnect. Images formed using data from the new digital correlator show over an order of magnitude improvement in dynamic range over the previous system. The ability to observe at low declinations has also been significantly improved.

GRB 170817A Associated with GW170817: Multi-frequency Observations and Modeling of Prompt Gamma-Ray Emission

Abstract We present our observations of electromagnetic transients associated with GW170817/GRB 170817A using optical telescopes of Chilescope observatory and Big Scanning Antenna (BSA) of Pushchino Radio Astronomy Observatory at 110 MHz. The Chilescope observatory detected an optical transient of ∼19m on the third day in the outskirts of the galaxy NGC 4993; we continued observations following its rapid decrease. We put an upper limit of 1.5 × 104 Jy on any radio source with a duration of 10–60 s, which may be associated with GW170817/GRB 170817A. The prompt gamma-ray emission consists of two distinctive components—a hard short pulse delayed by ∼2 s with respect to the LIGO signal and softer thermal pulse with T ∼ 10 keV lasting for another ∼2 s. The appearance of a thermal component at the end of the burst is unusual for short GRBs. Both the hard and the soft components do not satisfy the Amati relation, making GRB 170817A distinctively different from other short GRBs. Based on gamma-ray and optical observations, we develop a model for the prompt high-energy emission associated with GRB 170817A. The merger of two neutron stars creates an accretion torus of ∼10−2 M ⊙, which supplies the black hole with magnetic flux and confines the Blandford–Znajek-powered jet. We associate the hard prompt spike with the quasispherical breakout of the jet from the disk wind. As the jet plows through the wind with subrelativistic velocity, it creates a radiation-dominated shock that heats the wind material to tens of kiloelectron volts, producing the soft thermal component.

Progress with implementing the new research data management system at HartRAO

The Hartebeesthoek Radio Astronomy Observatory (HartRAO) participates in global radio astronomy and fundamental astronomy (space geodesy) research activities. Data and data products produced by HartRAO’s expanding range of on-site and off-site instrumentation must be archived and stored at HartRAO and made accessible to the scientific community. The data management and storage systems currently being used for managing fundamental astronomy data are not capable of handling the large volumes of data and have become obsolete. This necessitated the design and implementation of a next-generation Geodetic Research Data Management System (GRDMS), which complies with internationally accepted data service standards. We present the top-level conceptual model of the GRDMS and progress to date with developments of various sub-systems, data structuring and organisation within the sub-systems.

Detection of Five New RRATs at 111 MHz

Results of 111-MHz monitoring observations carried out on the Big Scanning Antenna of the Pushchino Radio Astronomy Observatory during September 1-28, 2015 are presented. Fifty-four pulsating sources were detected at declinations $-9^o < \delta < +42^o$. Forty-seven of these are known pulsars, five are new sources, and two are previously discovered transients. Estimates of the peak flux densities and dispersion measures are presented or all these sources.

Automated detection of Sun decametre radio bursts by the radio telescope URAN-3

The problem of the automated determination of the parameters of the sporadic decameter radio emission of the Sun with help of the radio-telescope URAN-3 taking into account its functions in the Ukrainian VLBI URAN structure is analyzed. An overview of alternative solutions of the problem is carried out. The technology of searching and detecting the radio bursts of type II and determination of such parameters as speed of drift in frequency sub bands, intensity, and duration and frequency width of bursts for a number of selected frequencies are considered. The effectiveness of the developed technology is confirmed by the results of long-term radioastronomical observations carried out at the URAN-3 radio telescope in 2011–2017. The formed on the basis of obtained and accumulated experimental data multiparameter relative database of solar activity is intended for further studies of the relation between the helio- and the geophysical phenomena for the purpose of developing forecasting models of geophysical manifestations of solar activity and evaluating the “geoefficiency” of active solar processes.

Using radio astronomical receivers for molecular spectroscopic characterization in astrochemical laboratory simulations: A proof of concept

We present a proof of concept on the coupling of radio astronomical receivers and spectrometers with chemical reactors and the performances of the resulting setup for spectroscopy and chemical simulations in laboratory astrophysics. Several experiments including cold plasma generation and UV photochemistry were performed in a 40 cm long gas cell placed in the beam path of the Aries 40 m radio telescope receivers operating in the 41-49 GHz frequency range interfaced with fast Fourier transform spectrometers providing 2 GHz bandwidth and 38 kHz resolution. The impedance matching of the cell windows has been studied using different materials. The choice of the material and its thickness was critical to obtain a sensitivity identical to that of standard radio astronomical observations. Spectroscopic signals arising from very low partial pressures of CH3OH, CH3CH2OH, HCOOH, OCS, CS, SO2 (<10-3 mbar) were detected in a few seconds. Fast data acquisition was achieved allowing for kinetic measurements in fragmentation experiments using electron impact or UV irradiation. Time evolution of chemical reactions involving OCS, O2 and CS2 was also observed demonstrating that reactive species, such as CS, can be maintained with high abundance in the gas phase during these experiments.

Bifrost: A Python/C++ Framework for High-Throughput Stream Processing in Astronomy

Radio astronomy observatories with high throughput back end instruments require real-time data processing. While computing hardware continues to advance rapidly, development of real-time processing pipelines remains difficult and time-consuming, which can limit scientific productivity. Motivated by this, we have developed Bifrost: an open-source software framework for rapid pipeline development. (a) Bifrost combines a high-level Python interface with highly efficient reconfigurable data transport and a library of computing blocks for CPU and GPU processing. The framework is generalizable, but initially it emphasizes the needs of high-throughput radio astronomy pipelines, such as the ability to process data buffers as if they were continuous streams, the capacity to partition processing into distinct data sequences (e.g. separate observations), and the ability to extract specific intervals from buffered data. Computing blocks in the library are designed for applications such as interferometry, pulsar dedispersion and timing, and transient search pipelines. We describe the design and implementation of the Bifrost framework and demonstrate its use as the backbone in the correlation and beamforming back end of the Long Wavelength Array (LWA) station in the Sevilleta National Wildlife Refuge, NM.

Results of Long-Term Monitoring of Maser Emission in the Star-forming Region G 10.623–0.383

The results of a study of the maser source G 10.623-0.383 in the λ = 1.35 cm H2O line using the 22-mradio telescope of the Pushchino Radio AstronomyObservatory (Russia) and in the main hydroxyl lines (λ = 18 cm) using the Nanзay Radio Telescope (France) are presented. Uncorrelated long-term variations of the integrated intensities and the velocity centroids with characteristic times of 11 yrs (mean value) and 32 yrs, respectively, are studied. The drift of the velocity centroid may be associated with maser condensations whose material is collapsing onto the OB cluster. It is shown that the H2O maser source contains maser condensation configurations on various scales over a long time, which evolve with time. OH maser emission was only detected in the main lines at 1665 and 1667 MHz. The flux densities of the strongest emission components were variable, but their radial velocities did not change. A Zeeman pair was found at 1667 MHz with a splitting of about 1.44 km/s, corresponding to a line-of-sight magnetic field of 4.1 mG, which was preserved over at least 25 years. The characteristics of the H2O andOHmaser variability suggests that the masers are located in different parts of G 10.623–0.383.

Atmospheric opacity estimation based on IWV derived from GNSS observations for VLBI applications

Thermal emission of atmospheric water vapor has a great influence on the calibration of radio astronomical observations at millimeter wavelengths. The phenomenon of an atmospheric water vapor emits noise signal and attenuates astronomical emission. At 22 GHz, integrated water vapor (IWV) obtained from global navigation satellite systems (GNSS) is strictly related to atmospheric opacity (tau_{0}), which is a crucial parameter for data calibration. Therefore, providing highly precise and accurate IWV from GNSS measurements may be an alternative for microwave radiometers. Whereas it is not possible to estimate IWV directly from GNSS measurements, its value is strictly correlated with the zenith wet delay (ZWD) that is estimated together with the coordinates during the GNSS positioning. In this study, differential and Precise Point Positioning methods for ZWD estimation are tested using two different tropospheric mapping functions: Vienna mapping function (VMF) and global mapping function (GMF). After positioning, the IWV conversion is performed using meteorological parameters derived from a meteorological station located near a GNSS site. Analyses for a 3-month period from June 1 to August 30, 2016, were conducted. Based on these, we obtained a very high correlation between IWV and tau_{0} as measured by the Torun 32 m radio telescope, which amounts about 0.95, for both PPP and differential solutions. Thus, techniques can be successfully used to estimate IWV and calculate tau_{0}. However, the linear regression coefficients depend on the used positioning method.

Refractive shift in the position of the pulsar PSR B0329+54, measured at 111, 610, and 2300 MHz

The results of an analysis of timing data for the pulsar PSR B0329+54 obtained in 1968–2012 on the Large Scanning Antenna of the Pushchino Radio Astronomy Observatory at 111 MHz, the 64 m DSS-14 telescope of the Jet Propulsion Laboratory at 2.3 GHz, and the 64 m telescope of the Kalyazin Radio Astronomy Observatory at 610 MHz are presented. The astrometric and spin parameters of the pulsar are derived at a new epoch. The coordinates of the pulsar and its proper motion measured at the three frequencies differ. These differences have a systematic character, and are interpreted as a secular, refractive shift in the apparent position of the pulsar that arises because it is observed through large-scale inhomogeneities of the interstellar medium, leading to variations in the angle of refraction.