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Full list of authors: Ho, Anna Y. Q.; Perley, Daniel A.; Yao, Yuhan; Svinkin, Dmitry; Postigo, A. de Ugarte; Perley, R. A.; Kann, D. Alexander; Burns, Eric; Andreoni, Igor; Bellm, Eric C.; Bissaldi, Elisabetta; Bloom, Joshua S.; Brink, Thomas G.; Dekany, Richard; Drake, Andrew J.; Fernandez, Jose Feliciano Agui; Filippenko, Alexei, V; Frederiks, Dmitry; Graham, Matthew J.; Hristov, Boyan A.; Kasliwal, Mansi M.; Kulkarni, S. R.; Kumar, Harsh; Laher, Russ R.; Lysenko, Alexandra L.; Mailyan, Bagrat; Malacaria, Christian; Miller, A. A.; Poolakkil, S.; Riddle, Reed; Ridnaia, Anna; Rusholme, Ben; Savchenko, Volodymyr; Sollerman, Jesper; Thoene, Christina; Tsvetkova, Anastasia; Ulanov, Mikhail; von Kienlin, Andreas.--This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., Dirty fireballs are a hypothesized class of relativistic massive-star explosions with an initial Lorentz factor Γinit below the Γinit ∼ 100 required to produce a long-duration gamma-ray burst (LGRB), but which could still produce optical emission resembling LGRB afterglows. Here we present the results of a search for on-axis optical afterglows using the Zwicky Transient Facility (ZTF). Our search yielded seven optical transients that resemble on-axis LGRB afterglows in terms of their red colors (g − r > 0 mag), faint host galaxies (r > 23 mag), rapid fading (dr/dt > 1 mag day−1), and in some cases X-ray and radio emission. Spectroscopy of the transient emission within a few days of discovery established cosmological distances (redshift z = 0.876 to 2.9) for six of the seven events, tripling the number of afterglows with redshift measurements discovered by optical surveys without a γ-ray trigger. A likely associated LGRB (GRB 200524A, GRB 210204A, GRB 210212B, and GRB 210610B) was identified for four events (ZTF 20abbiixp/AT 2020kym, ZTF 21aagwbjr/AT 2021buv, ZTF 21aakruew/AT 2021cwd, and ZTF 21abfmpwn/AT 2021qbd) post facto, while three (ZTF 20aajnksq/AT 2020blt, ZTF 21aaeyldq/AT 2021any, and ZTF 21aayokph/AT 2021lfa) had no detected LGRB counterpart. The simplest explanation for the three "orphan" events is that they were regular LGRBs missed by high-energy satellites owing to detector sensitivity and duty cycle, although it is possible that they were intrinsically subluminous in γ-rays or viewed slightly off-axis. We rule out a scenario in which dirty fireballs have a similar energy per solid angle to LGRBs and are an order of magnitude more common. In addition, we set the first direct constraint on the ratio of the opening angles of the material producing γ-rays and the material producing early optical afterglow emission, finding that they must be comparable. © 2022. The Author(s). Published by the American Astronomical Society., D.A.P.'s contribution was performed in part at the Aspen Center for Physics, which is supported by National Science Foundation (NSF) grant PHY-1607611. This work was partially supported by a grant from the Simons Foundation. D.F., A.T., and M.U. acknowledge support from RSF grant 21-12-00250. D.A.K. and J.F.A.F acknowledges support from Spanish National Research Project RTI2018-098104-J-I00 (GRBPhot). H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining Grant #1829740, Brinson and Moore Foundations. J.F.A.F. acknowledges support from the Spanish Ministerio de Ciencia, Innovación y Universidades through the grant PRE2018-086507. A.V.F.'s group at U.C. Berkeley is grateful for assistance from the Christopher R. Redlich Fund and many individual donors., With funding from the Spanish government through the Severo Ochoa Centre of Excellence accreditation SEV-2017-0709.

Modern interferometric imaging relies on advanced calibration that incorporates direction-dependent effects. Their increasing number of antennas (e.g. in LOFAR, VLA, MeerKAT/SKA) and sensitivity are often tempered with the accuracy of their calibration. Beam accuracy drives particularly the capability for high dynamic range imaging (HDR - contrast > 1:$10^6$). The Radio Interferometric Measurement Equation (RIME) proposes a refined calibration framework for wide field of views (i.e. beyond the primary lobe and first null) using beam models. We have used holography data taken on 12 antennas of the Very Large Array (VLA) with two different approaches: a `data-driven' representation derived from Principal Component Analysis (PCA) and a projection on the Zernike polynomials. We determined sparse representations of the beam to encode its spatial and spectral variations. For each approach, we compressed the spatial and spectral distribution of coefficients using low-rank approximations. The spectral behaviour was encoded with a Discrete Cosine Transform (DCT). We compared our modelling to that of the Cassbeam software which provides a parametric model of the antenna and its radiated field. We present comparisons of the beam reconstruction fidelity vs. `compressibility'. We found that the PCA method provides the most accurate model. In the case of VLA antennas, we discuss the frequency ripple over L-band which is associated with a standing wave between antenna reflectors. The results are a series of coefficients that can easily be used `on-the-fly' in calibration pipelines to generate accurate beams at low computing costs., 16 pages, 15 figures, 2 online videos, Accepted in MNRAS. For the online videos, see http://www.youtube.com/watch?v=oc9lLxJy3Ow and http://www.youtube.com/watch?v=3RYrBxCyebk

Analysis of the radio synchrotron and X-ray inverse-Compton emission from radio-loud active galaxies allows us to determine their particle acceleration processes and electron energy spectra. Previous studies have provided new constraints on the total energy budget and particle content of powerful radio galaxies and quasars; however, in most cases the sources are too faint in the X-ray to obtain spatial information. We present archival and new multi-frequency radio observations from the VLA and GMRT, and XMM-Newton observations of the bright FRII radio galaxy 3C353 which lies on the edge of the X-ray-luminous cluster Zw 1718.1-0108. The X-ray observations detect both the inverse-Compton emission from the radio galaxy lobes and thermal emission from the hot phase of the intracluster medium. We discuss the properties of the particle energy spectrum as a function of position in the lobe, as well as the properties of the merging cluster., Comment: 5 pages; to appear in "Extragalactic Jets: Theory and Observation from Radio to Gamma Ray", eds. T. A. Rector and D. S. De Young, ASP conference series

Using new deep VLA and HST observations of the large-scale jet in 3C273 matched to 0.3" resolution, we have detected excess near-ultraviolet emission (300 nm) above a synchrotron cutoff spectrum accounting for the emission from radio through optical (3.6 cm - 620 nm). This necessitates a two-component model for the emission. The radio-optical-X-ray spectral energy distributions suggest a common origin for the UV excess and the X-rays from the jet., Comment: Accepted for publication by A&A Letters (4 pages, 3 figures)

We report on two programs to address differential evolution between the radio-loud and radio-quiet quasar populations at high (z>4) redshift. Both programs entail studying the radio properties of optically-selected quasars. First, we have observed 32 optically-selected, high-redshift (z>4) quasars with the VLA at 6 cm (5 GHz). These sources comprise a statistically complete and well-understood sample. We detect four quasars above our 3-sigma limit of ~0.15 mJy, which is sufficiently sensitive to detect all radio-loud quasars at the probed redshift range. Second, we have correlated 134 z>4 quasars, comprising all such sources that we are aware of as of mid-1999, with FIRST and NVSS. These two recent 1.4 GHz VLA sky surveys reach 3-sigma limits of approximately 0.6 mJy and 1.4 mJy respectively. We identify a total of 15 z>4 quasars, of which six were not previously known to be radio-loud. The depth of these surveys does not reach the radio-loud/radio-quiet demarcation luminosity density (L(1.4 GHz) = 10^32.5 h(50)^(-2) ergs/s/Hz) at the redshift range considered; this correlation therefore only provides a lower limit to the radio-loud fraction of quasars at high-redshift. The two programs together identify eight new radio-loud quasars at z>4, a significant increase over the seven currently in the published literature. We find no evidence for radio-loud fraction depending on optical luminosity for -25 > M_B > -28 at z~2, or for -26>M_B>-28 at z>4. Our results also show no evolution in the radio-loud fraction between z~2 and z>4 (-26>M_B>-28).

Maps of 212 extragalactic radio sources at 4.9 GHz are shown in Stokes I along with linear polarization vectors. The objects have a declination range of 0° to -35° and were chosen from the Hewitt & Burbidge quasar catalog with a spectral index less than -0.5 and the NVSS survey with a minimum 1.4 GHz flux density greater than 300 mJy. The observations were made with the Very Large Array in its B configuration, and the images have a typical resolution of 2''. One hundred ninety-five objects were resolved; 108 of the sources are quasars, and another 51 have been identified as galaxies.

Early large scale radio surveys of the sky were made with instruments with poor imaging quality and were limited to measuring positions and brightnesses of discrete sources. In recent decades radio interferometric arrays have dramatically increased their speed, sensitivity and ability to image the sky and several large scale radio surveys are currently being made with imaging instruments. One of these surveys is discussed in this paper.

In 1984 Perley and Erickson proposed a 73.8 MHz [4 meter wavelength] observing system at the VLA site (NRAO Scientific Memo #146). They proposed a stand-alone antenna system that would feed its signals into an existing spare channel of the VLA waveguide and utilize a separate correlator. Over the 35 km VLA baselines this system would produce images with 20 arcsec resolution, unprecedented at this frequency. The major technical problems are ionospheric refraction and interference. Some doubt existed as to whether or not it would be possible to cope with the large, rapidly-changing ionospheric phase fluctuations to be expected over 35 km baselines. Thus it was proposed, as a first step in the development, that 73.8 MHz feeds be installed in the present VLA dishes and that trial observations be made to prove that techniques such as self-calibration can be successful. Eight dishes now have 73.8 MHz instrumentation and a number of radio source images have been made with this initial system.

The general relation between interferometric data and sky brightness requires the use of three-dimensional Fourier transforms. Only in special cases does the standard two-dimensional Fourier relations result in images free of distortions. For the VLA, use of two-dimensional transforms introduces errors which are important at low frequencies and high resolutions. We review options and progress in solving the computational problems associated with the full solution.

73.8 MHz instrumentation for the VLA is being developed and is currently installed on 8 VLA dishes. Test observations of strong radio sources have been made. We describe techniques that we have developed to analyze these test observations and we present examples of our first maps.

We show that recent radio and optical observations of polarized radiation from well-resolved high redshift quasars and radio galaxies rule out the cosmological rotation of the plane of polarization claimed recently by Nodland and Ralston. A least squares fit to the radio data has a slope only 2% of their claimed effect., This is a revision of a paper submitted to Phys Rev Letters. A number of modest changes have been made, including using more radio data, really replacing the optical data on Cygnus A with that on 3C265, and adding to the discussion. Three pages and three figures

We report observations of the four-image gravitational lens system Q2237+0305 with the VLA at 20 cm and 3.6 cm. The quasar was detected at both frequencies (\approx 0.7 mJy) with a flat spectrum. All four lensed images are clearly resolved at 3.6 cm, and the agreement of the radio and optical image positions is excellent. No radio emission is detected from the lensing galaxy, and any fifth lensed quasar image must be fainter than \sim 20% of the A image flux density. Since the optical quasar images are variable and susceptible to extinction, radio flux ratios provide the best measurement of the macrolensing magnification ratios. The radio B/A and C/A image flux ratios are consistent with the observed range of optical variations, but the D/A ratio is consistently higher in the radio than in the optical. The radio ratios are consistent with magnification ratios predicted by lens models, and weaken alternative interpretations for Q2237+0305. More accurate radio ratios can distinguish between the models, as well as improve our understanding of both microlensing and extinction in this system., 1 postscript file, 13 pages. To appear in AJ (1996.09), Submitted 1996.03.13, Accepted 1996.05.20

There are now approximately two dozen operating interferometers in astronomy, with more under construction or in planning. The wide distribution of interferometer arrays, and their acceptance as essential tools in astronomy are a result of the remarkable flexibility and imaging capabilities of modern arrays. Much of the success of these arrays’ is due to advances in data processing and imaging brought about by innovative and powerful algorithms.

The ALFA mission is designed to map the entire sky at frequencies between approximately 0.3 and 30 MHz with angular resolution limited by interstellar and interplanetary scattering. Most of this region of the spectrum is inaccessible from the ground because of absorption and refraction by the Earth’s ionosphere. A wide range of astrophysical questions concerning solar system, galactic, and extragalactic objects could be answered with high resolution images at low frequencies, where absorption effects and coherent emission processes become important and the synchrotron lifetimes of electrons are comparable to the age of the universe.

Un catalyseur de 1992 radiosource de plan galactique, observees en VLA, comprenant les positions, les densites de flux et les diametres, est presente

Observations with arcsecond-resolution interferometers can be used to detect motion or changes of the large scale structure associated with core dominated objects. If these arcsecond structures are expanding at relativistic velocities, detectable changes should be measureable within a few years. Indirect estimates of jet velocities can be made by a number of arguments, but none are model independent or free of dependence upon poorly established parameters. Application of some of these methods are given on sources with established VLB structure.

L'absence de detection des jets optiques etendus de NGC 1097 a 20 cm amene a conclure que ces jets ne sont pas la consequence de l'emission synchrotron mais plutot de l'emission par rayonnement de freinage thermique. Le gaz est approximativement a 10 6 K et la densite electronique est de 2 cm −3 . On observe un anneau brillant d'emission non thermique a un rayon de 580 h −1 pc du noyau de NGC 1097

NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ∼ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s−1 Mpc−1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.

The Homestake Collection System Pipelines and Intakes were built in rugged terrain which has a short construction season. The contractor chose to use steel pipe for this pipeline, which varies in size from 21-in. to 96-in. The design criteria for the steel pipe are presented in detail. The design details of the diversion dams, constructed of native materials, and designed to be overtopped are presented. The intakes and measuring flume structures are cast-in-place, reinforced concrete structures. The contractor’s operations were governed by the short construction season and by the difficulty of access along the Collection System Pipelines.

WE report here the results of extensive observations of a new series of outbursts from Cyg X-3 which we commenced following the recent IAU telegram alert from Sir Martin Ryle. A high degree of linear polarisation has been discovered in one of the recent outbursts. The degree of polarisation changes over a period of 17 d and reaches a maximum of 14%. The observations indicate a high degree of order in the source magnetic field and that a thermal plasma coexists with the radiating relativistic electrons. In addition, a new upper limit of 0.05″ has been obtained for the angular size of Cyg X-3, together with an improved position for the source.

The jet in the radio galaxy NGC6251 (Waggett et al. 1977) has been observed with the VLA using resolutions from 1.15″ to 15″ at 1370, 1480, 1662 and 4885 MHz, and a resolution of 50″ at 1446 and 1662 MHz. The resulting maps (e.g. Figure 1) give exceptionally detailed information on the distributions of the total and polarized intensities over the jet.

NGC 6251, a 14th mag elliptical galaxy, was shown by Waggett et al. (1977) to have large-scale radio emission features with a total angular extent of ~ 1.1°, which corresponds to a projected linear size of about 1.7 Mpc (HO = 75 km s-1 Mpc-1). A bright radio jet links a central core source embedded in NGC 6251 to the extended emission on the northwest side of the galaxy.

We report discovery of a pair of quasars at a redshift of 1.345, separated by 4”.2 in projection, apparently associated with the radio source PKS 1145-071. The optical intensity ratio of the two images is approximately 2.5. The spectra are very similar, and all emission lines except for the C IV λI549 have the same equivalent widths, within the error bars. The redshift difference based on the C IV line alone, which is the strongest feature, and on the cross-correlation of the two spectra including the C IV line, is approximately 250 ± 100 km s^(-1) in the rest frame. If this discrepant emission line is excluded, the redshift difference drops to approximately 100 ± 100 km s^(-1), and is consistent with zero. Thus, on the basis of the optical data alone, we would have concluded that this double QSO is another example of gravitational lensing. However, the radio source is single and unresolved at all VLA frequencies, and positionally coincident with the brighter of the two optical images. The fainter of the two optical components is at least a factor of 500 fainter in the radio. This dramatic difference in L_(opt)/L_(radio) between the two components suggests that the system is a genuine binary quasar, and the first such well-documented case. Assuming that the two QSO’s are gravitationally bound, we derive a lower limit to the total mass of the system of ~ 10^(11)h^(-1)M_⊙ this is the first such direct determination of a quasar mass. The close projected separation of the pair (~ 20h^(-1) kpc) and the small velocity difference are suggestive of an interaction, which may be causally related to the QSO activity, and of the existence of a parent group or cluster, which would be a very interesting find in itself. In the view of this discovery, it is plausible that some other, previously reported gravitational lenses may be really pairs of physically distinct quasars.

As part of the VLA calibration program, 404 small angular size sources have been observed in the “A” array at both 6 and 20 cm with resulting resolutions of 0.4″ and 1.2″ respectively. Use of self-calibration techniques has allowed a search for associated extended structure to a level of ~0.3% of the peak. Here we report preliminary analysis of the results.

Bridle (this volume) has summarized the overall characteristics of the jets found in numerous low-luminosity and some high-luminosity radio sources. Previous observations made with the partially completed VLA at wavelengths of 6 and 20 cm indicated that 3C449 was an archetypal radio source obeying all the “rules” summarized by Bridle. New observations with the VLA of the polarization structure at 6 and 20 cm have destroyed this simple picture and identify 3C449 as a “rogue” jet source.

THE sudden increase in radio flux observed1 from the direction of Cygnus X-3 on September 22–23, 1972, occurred just as we began a four-antenna very-long-baseline interferometry experiment that involved a pair of radio telescopes in Green Bank, West Virginia and another pair in Massachusetts (Table 1). We were able to take advantage of this opportunity to observe Cygnus X-3 interferometrically on September 24 and report here the negative results of these observations.

A narrow-emission-line companion of the quasar PKS 1614 + 051 was reported earlier as a probable galaxy at a redshift of 3.218, which would have made it by far the most distant galaxy known at the time. We report here on new radio and optical imaging, and optical and near-IR spectroscopy of the PKS 1614 + 051 system. We argue that the data support and reinforce the original interpretation of the companion object as a mildly active galaxy, possibly a marginal Seyfert.2. The object has a detectable and marginally resolved optical continuum, but was not detected at radio .wavelengths. The ionization state is low, and the emission lines are fairly narrow. The improved redshift for the companion, based on the Lyα line alone, is 3.215 ± 0.002. New Lyα images show interesting morphology of extended emission-line gas, suggestive of a possible tidal interaction with the neighboring QSO. Two other, fainter objects in the immediate proximity of the QSO may also be associated with the system. If this is the case, we may be seeing a group of galaxies in the early stages of formation.

A continuum VLA survey of the Galactic plane has been performed at 1.5 GHz, with most fields complete to about 30 mJy peak flux density. Measurements of position, peak, and total flux density have been obtained for 471 compact sources. An excess of sources above that predicted from extragalactic source counts is found for longitudes less than 40 deg at all flux-density intervals. With the exception of 86 compact sources that lie within 2.4 arcsec of a source in the radio recombination-line survey of Lockman (1988), source counts are shown to agree with extragalactic source counts for all flux-density and longitude intervals. 21 references.

We have surveyed 58 fields near rich clusters of galaxies with the Very Large Array using scaled arrays in the B/C and/or C/O configurations at 1�5 GHz and 4�9 GHz. The fields were centred on steep spectrum sources in or near clusters that were earlier surveyed with lower resolution telescopes. The whole-field maps at 1�5 GHz are given and a list of 940 sources with 1�5 GHz flux densities down to -1 mJy is presented. Spectral indices of sources within 5' of the field centres are given. Complete flux-limited samples of sources are used to establish a criterion for cluster membership. Sources with total 1�5 GHz flux density >20 mjy and closer to the cluster centre than 0�28 of the cluster radius (a total of 57 sources) are accepted as cluster members.

The secular decrease in the flux of the supernova remnant Cassiopeia A has been measured at many radio frequencies. Observations are reported which indicate that this flux decrease has halted at 38 MHz and that the flux is increasing at this frequency. This may indicate that a new era of activity has begun in this object.