Constructing the EVLA while operating the VLA

Context. The G25.65+1.04 source is one of the few known ‘super-flare’ water masers in the Milky Way, but in contrast to other super-flare sources, it remains the least studied. In fact, even the nature of the source driving the water maser is still unclear. Aims. With this project, we aim to clarify the composition and properties of the G25.65+1.04 region by means of examining the parameters of the continuum sources and establishing their association with masers of different types. Methods. Our previous VLA (Karl G. Jansky Very Large Array) observation detected four continuum peaks (VLA 1-4), three of which (VLA 1-3) were closely spaced and presented a linear orientation. However, the observation, which used the VLA B configuration, lacked the spatial resolution to resolve individual sources. A higher-resolution (A configuration) VLA observation of the continuum and spectral lines was conducted in 2019 using the L, S, C, and Ku bands. Results. For the first time, the continuum source VLA 1 – associated with the flaring water maser – is resolved into two components: VLA 1A and 1B. The component VLA 1A and the water maser are found to spatially coincide and are thought to be powered by the same source, a protostar at an early stage of evolution showing active ejection. We argue that VLA 2 pinpoints an actively ejecting high-mass protostar, as it is associated with a 6.7 GHz methanol maser and a magnetised jet traced by a 22 GHz H2O maser. Highly polarised OH maser emission is detected in the vicinity of VLA 1-2, with the brightest OH maser found in VLA 2. The magnetic field, identified from the OH maser emission, ranges from ∼ + 0.4 mG in VLA 1A to ∼ − 8 mG in VLA 2. Conclusions. The G25.65+1.04 region is found to consist of at least two young stellar objects: VLA 1A and VLA 2. Both sources are found to be at an active accretion and ejection stage of evolution.

We report centimeter continuum observations with the VLA and the VLBA as well as mid-infrared observations with COMICS/SUBARU toward the components of the YLW 15 very young binary system, VLA 1 and VLA 2. The centimeter emission of the two components traces partially thick free-free emission, likely due to collimated, ionized winds. VLA 1 is an embedded protostar, undetected in the near-IR, and possibly in the Class 0 to Class I transition and powering a Herbig-Haro outflow. Its mid-IR emission appears slightly resolved with a diameter of ~16 AU, possibly tracing circumstellar material from both the envelope and the disk. VLA 2 is a typical Class I object, unresolved in the mid-IR, and is the responsible of the strong X-ray emission associated with YLW 15. The expected centimeter ''peri-stellar'' emission associated with the X-ray emission is not detected with the VLBA at 6 cm likely due to the high optical depth of the free-free emission. Strikingly, the near to mid-IR properties of YLW 15 suggest that VLA 1 is a more embedded YSO, or alternatively, less luminous than VLA 2, whereas orbital proper motions of this binary system indicate that VLA 1 is more massive than VLA 2. This result is apparently against the expected evolutionary scenario, where one expects that the more massive YSO in a binary system is the more evolved and luminous YSO. Finally, the nearby source YLW 16A is detected with the VLA, its position coincides with reported near-IR and X-ray sources.

We describe the world's largest synthesis radio telescope, the Very Large Array (VLA), and how it can be used to complement observations with the Solar and Heliospheric Observatory (SOHO) and the Yohkoh solar spacecraft. The VLA provides images with high spatial and temporal resolution, often across the visible solar disk. The VLA also detects nonthermal radiation that is not observed with SOHO and Yohkoh, and provides estimates for the coronal magnetic field strengths that are not directly measured by these spacecraft. The VLA data can be combined with SOHO CDS, SOHO EIT, or Yohkoh SXT observations to provide new insights to the compact, variable sources, called blinkers and bright points, in the solar transition region or low corona. A new 400 cm VLA system provides images of nonthermal burst activity associated with Coronal Mass Ejections (CMEs), and may detect thermal emission from CMEs, that can be compared with SOHO's LASCO and EIT instruments to obtain new information about the origin and evolution of CMEs.

The Expanded Very Large Array (EVLA) project is currently under way to upgrade the Very Large Array (VLA) to improve the sensitivity, bandwidth, spectral resolution and frequency coverage of the existing array of 27 radio telescopes [1]. The EVLA receivers will provide continuous frequency coverage from 1 GHz to 50 GHz. Three of the cryogenically cooled EVLA receivers will provide octave band coverage for the L-band (1 GHz to 2 GHz), S-Band (2 GHz to 4 GHz) and C-band (4 GHz to 8 GHz).

view Abstract Citations (96) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Two-dimensional VLA maps of solar bursts at 15 and 23 GHz with arcsec resolution Marsh, K. A. ; Hurford, G. J. Abstract Three small, impulsive solar-microwave bursts (peak fluxes 4.9, 3.0, and 0.4 sfu) were observed during 1979 September 7-9, using the Very Large Array (VLA) at 15.05 or 22.5 GHz. The data from 10 antennas distributed on three arms of the array provide the first two-dimensional burst images with spatial resolution as high as 1.0 x 0.75 arcsec. Comparison with optical data showed in the impulsive phase of all three flares, the microwave emission was dominated by a compact source located between the H-alpha kernels. In the post-impulsive phase, the microwave source was larger and elongated in a direction consistent with the orientation of the magnetic field lines joining the H-alpha kernels. These results are interpreted to imply that the initial energy release occurs near the top of the magnetic arch joining the H-alpha kernels. Publication: The Astrophysical Journal Pub Date: September 1980 DOI: 10.1086/183335 Bibcode: 1980ApJ...240L.111M Keywords: Antenna Arrays; H Alpha Line; Microwave Emission; Solar Radio Bursts; Spatial Resolution; Microwave Antennas; Phased Arrays; Solar Flares; Very Large Array (Vla); Solar Physics full text sources ADS |

The Expanded Very Large Array (EVLA) project is the next generation instrument for high resolution and high sensitivity long-millimeter to short-meter wavelength radio astronomy. It is currently funded by NSF, with completion scheduled for 2012. The EVLA will upgrade the VLA with new feeds, receivers, data transmission hardware, correlator, and a new software system to enable the instrument to achieve its full potential. This software includes both that required for controlling and monitoring the instrument and that with emphasis on the scientific functions related to the telescope. The primary goals of the software are: to maximize the scientific return of the EVLA; provide ease of use, for both novices and experts; exploit commonality amongst all NRAO telescopes where possible. The software design methodology includes detailed initial use-cases and requirements from the scientists, intimate interaction between the scientists and the programmers during design and implementation, and rapid prototyping and development cycles (as short as a week). This manuscript is an update of a similar description published for the SPIE meeting two years ago; a more full description and background can be found there, while this document concentrates on the changes since then, specifically in the area of the high level design and pre-observing software (user authentication; proposal preparation, submission, and handling; observation preparation; and observation scheduling).

The National Radio Astronomy Observatory (NRAO) operates the Very Large Array (VLA) Radio Observatory on the Plains of San Augustin in New Mexico, and the Very Long Baseline Array (VLBA) with 10 antenna locations from Hawaii to St. Croix. Harmful radio frequency interference (RFI) is a growing problem for the VLA and the VLBA, and for that matter, all Earth-based radio astronomy. The paper describes an automated monitor system that has been recently installed at the VLA for use in identifying and cataloging RFI. The operation of the VLA and VLBA are summarized and the reason interference is a problem is explained. Initial results of the monitoring are included as are plans for future expansion of the program.

We have used the Very Large Array (VLA) in C configuration to carry out a sensitive 20-cm radio survey of regions of sky that have been surveyed in the far-infrared (FIR) over the wavelength range 5--200 μm with ISO (Infrared Space Observatory) as part of the European Large-Area ISO Survey (ELAIS). As usual in surveys based on a relatively small number of overlapping VLA pointings, the flux limit varies over the area surveyed: from a 5σ limit of 0.135 mJy over an area of 0.12 deg2 to 1.15 mJy or better over the whole region covered of 4.22 deg2. In this paper we present the complete radio catalogue of 867 sources, 428 of which form a complete sample in the flux range 0.2--1.0 mJy. These regions of sky have previously been surveyed to shallower flux limits at 20 cm with the VLA as part of the VLA D configuration NVSS (full width at half-maximum, FWHM=45 arcsec) and VLA B configuration FIRST (FWHM=5 arcsec) surveys. Our whole survey has a nominal 5σ flux limit a factor of 2 below that of the NVSS; 3.4 deg2 of the survey reaches the nominal flux limit of the FIRST survey and 1.5 deg2 reaches 0.25 mJy, a factor of 4 below the nominal FIRST survey limit. In addition, our survey is at a resolution intermediate between the two surveys and thus is well suited for a comparison of the reliability and resolution-dependent surface brightness effects that affect interferometric radio surveys. We have carried out a detailed comparison of our own survey and these two independent surveys in order to assess the reliability and completeness of each. Considering the whole sample, we found that to the 5σ nominal limits of 2.3 and 1.0 mJy, respectively, the NVSS and FIRST surveys have a completeness of 96+2-3 and 89+2-3 per cent and a reliability of 99+1-2 and 94+2-2 per cent.

For nearly two decades, the aperature synthesis telescope known as the Very Large Array (VLA) has been providing a wealth of data on all types of astronomical objects. This telescope fills the need for more powerful and more sensitive instruments to gather data on a vast range of plasma phenomena in astrophysical settings. Currently the VLA is capable of observing at eight radio frequency bands (four corresponding to important spectral lines) with sensitivities on the order of 10−29 Wm −2 Hz −1, or 10−3 Jansky (1 mJy), and noise levels ten times lower. This paper describes the VLA and its capabilities, and describes how researchers interested in plasma astrophysics can use the instrument.

Based on the two-epoch European Very Long Baseline Interferometry (VLBI) Network (EVN) archive data from OH line observations of IIZw 096, we confirm that the high-resolution OH emission in this source mainly comes from two spots (OH1 and OH2) of component (comp) D1 of this merging system. We found no significant variations in the OH 1667 MHz line emission, including flux densities and peak positions. The OH 1665 MHz line emission is detected at about the 6σ level in the OH1 region by combining two epochs of EVN observations. By using archival data from the Very Long Baseline Array (VLBA), Very Large Array (VLA), and Atacama Large Millimeter Array (ALMA) observations, we investigated the properties of the environment of this component through H I, CO(3-2), and HCO+(4-3) lines and the multi-band radio continuum emission. We found that the comp D1 shows the brightest CO, HCO+ line emission, as well as multi-band radio continuum emission. The environment around D1 shows no clear velocity structure associated with circular motions, making it different from most other OH megamasers (OHMs) in the literature, which might have been caused by an effect during the merger stage. Meanwhile, we found that the CO emission shows three velocity structures around D1, including the central broad full width at half maximum (FWHM) region, the double-peak region where the CO line profile shows two separated peaks, and the region of the high-velocity clouds where the CO line peaks at a high velocity (∼11 000 km s−1). Similarly, H Iobservations in absorption also show high-velocity clouds around the D1 region, which might be due to inflows caused by the merging of two or more galaxy components. Based on the high-resolution K-band VLA and L-band VLBA observations of the radio continuum emission, we derived the brightness temperature in the range 105 K–106 K, which is consistent with other starburst dominant OHM sources in the literature. The multi-band VLA observations show that the radio continuum emission of comp D might also have contributions from free-free emission in addition to synchrotron emission. As a consequence, these results support a starburst origin for the OHMs, without the presence of an active galactic nucleus (AGN).

The goal of the Expanded Very Large Array (EVLA), project is to upgrade a world-class astronomical instrument in the meter-to-millimeter wavelength bands. The project combines modern technologies with the sound design of the existing Very Large Array (VLA) to increase by an order of magnitude the sensitivity, resolution, and frequency coverage of the existing instrument. This paper discusses the techniques used to maintain phase coherence of the EVLA system. The enhancements to the VLA system include improved feeds and receivers, new Local Oscillator (LO) and Intermediate Frequency (IF) systems, a fiber optic LO distribution system, high speed digitizers, 10Gbps digital links, a dense wavelength division multiplexed fiber transmission system, and a new high speed correlator. The phase requirement for the LO system requires that a phase stability of 2.8 picoseconds per hour at 40 GHz be maintained across the entire array. To accomplish this, a near real time continuous measurement will be made of the phase delay in the fiber optic cable distributing the LO reference signals to each antenna. This information will be used by the correlator to set the delay on each of the baselines in the array.

The design of the National Radio Astronomy Observatory's Expanded Very Large Array (EVLA) project is approaching completion. Four of the twenty-seven antennas have been upgraded into the final configuration. The 2200 miles of fiber optic cables have been installed underground and are functional. The master oscillator and the round trip phase hardware have been operating uninterrupted since November 2003. Hundreds of hours of test observations have been performed as we start the task of characterizing the upgraded system. This paper discusses the results of this testing and describes the techniques used to maintain phase coherence of the EVLA LO chain and of the new wideband receivers. The enhancements to the VLA system include a new local oscillator (LO) system, a fiber optic LO distribution system, and a digital round trip phase measurement system. The phase requirement for the LO system requires that the long term phase drift slope be less than 6.0 picoseconds per 30 minutes at 40 GHz and be maintained across the entire array. To accomplish this, a near real time continuous measurement is made of the phase delay in the fiber optic cable distributing the LO reference signals to each antenna. This information is used by the correlator to set the phase on each of the baselines in the array.

Observations of the 15:22 UT flare of 24 June 1980 were made using the Very Large Array (VLA) at 6 cm wavelength simultaneously with the Hard X-ray Imaging Spectrometer (HXIS) aboard the Solar Maximum Mission. It was found that at the peak of the impulsive phase, the brightest microwave point appeared to lie between the soft (3.6–8.0 keV) and hard (22–30 keV) X-ray maxima, which were themselves separated by ∼ 20″ (Kundu et al., 1984). Since the publication of these results, we have analyzed the imaging data from the Ultraviolet Spectrometer Polarimeter (UVSP) with the goal of narrowing the possible interpretations of the event. Like the VLA and HXIS, the UVSP observations provide information about the location of the primary electrons; the observations taken together suggest that the fast electrons were symmetrically distributed within the flare loop.

\n We present multi-epoch radio maps of the microquasar Cygnus X-3 \nobtained with the Very Large Array (VLA). \nThe observations were carried out as a Target-of-Opportunity (ToO)\nproject triggered by a series of strong (>5 Jy)\nradio outbursts in September 2000. We find that Cygnus X-3 was well resolved\nand clearly elongated in the North-South direction at the VLA resolution in the weeks after\nthe triggering events. In particular, the VLA map from our final\nepoch of observation perfectly shows the development of a two-sided radio jet extending\nover ~0.05 pc scales. We interpret\nboth the proper motion and the brightness asymmetry between the jet components \nin the framework of special relativity effects. Assuming a distance of\n10 kpc, the true jet velocity that we derive is close to $0.5c$ with a large angle with the line of sight. \nThe possible connection between the VLA bipolar jets and the elongated \none-sided structures observed at milli-arcsecond angular scales is also discussed.\n \n \n

The Very Large Array (VLA) has been used at 20 cm wavelength to study the evolution of a burst loop with 4″ resolution on timescales as short as 10 s. The VLA observations show that the coronal loop began to heat up and change its structure about 15 min before the eruption of two impulsive bursts. The first of these bursts occurred near the top of the loop that underwent preburst heating, while the second burst probably occurred along the legs of an adjacent loop. These observations evoke flare models in which coronal loops twist, develop magnetic instabilities and then erupt. We also combine the VLA observations with GOES X-ray data to derive a peak electron temperature of Te = 2.5 × 107 K and an average electron density of Ne ≈ 1 × 1010 cm−3 in the coronal loop during the preburst heating phase.