The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈2 5), sensitivity (a 1σ goal of 70 μJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. >−40°), a total of 33 885deg 2. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.
Mariner 2 obtained data on the interplanetary plasma during the period August 29, 1962, through January 3, 1963. The daily average plasma velocity is presented and compared with data on cosmic‐ray diurnal variations and with indices of solar and geomagnetic activity for this period. The only strong correlation found is that between plasma velocity and the geomagnetic index Kp. The plasma velocity showed a very strong 27‐day recurrence tendency and a close association with M‐region geomagnetic storms, indicating that solar M‐regions are emitters of high‐velocity plasma. No dependence of plasma velocity on solar distance between 1.0 and 0.7 AU could be detected.
The dependence of the counting rate of a cosmic ray detector on the asymptotic directions of approach of the primary cosmic radiation is discussed. By means of a simulation of the geomagnetic field that uses spherical harmonics up to the sixth degree, and an arbitrary anisotropy in the primary cosmic radiation, a method for calculating the time variations in the counting rate of a cosmic ray detector is developed. Resolving the arbitrary anisotropy as a Fourier series in longitude, the amplitude and phases of the diurnal (24‐hourly) and semidiurnal (12‐hourly) components of the daily variation are calculated for a number of stations. No simple relationship is observed between the phases and the latitudes and longitudes, geographic or geomagnetic. Moreover, the theoretical calculations point out that a difference of more than five hours between the diurnal phases at two different places could arise purely from the known geomagnetic configuration. A study of the time‐averaged diurnal component of the daily variation experimentally observed by 22 neutron monitors during the International Geophysical Year (1957–1958) reveals good agreement with the theoretical calculations and leads to the following conclusions: (1) The results are consistent with an anisotropy that is independent of rigidity in the range 1–200 bv, the exponent of the power law which fits the data being 0.0±0.05. (2) The anisotropy varies as the cosine of the asymptotic latitude and has a maximum in the direction 85° to the east of the earth‐sun line. (3) The maximum amplitude of the average anisotropy is 4×10−3 times the average cosmic ray flux.
Seven examples of the observation of intense fluxes of ≈10‐Mev charged particles associated with disturbances in the interplanetary medium during 1966 are discussed, and detailed data from four of them are presented. It is shown that there is an approximately one‐to‐one correspondence between such events and the onset of Forbush decreases initiated by solar flares. The particle fluxes exhibit characteristic time profiles, with a typical time scale of 6 hours. The particle fluxes are strongly anisotropic, and the direction of the anisotropy shows drastic temporal variations during the onset of the Forbush decrease. The fluxes of particles of energy ≈10 Mev are frequently considerably greater, while the energy spectra are usually noticeably softer than those observed during the preceding flare effect. A bidirectional anisotropy is commonly observed following the decreasing intensity phase of a Forbush decrease, the two directions of maximum flux being aligned parallel and antiparallel to the interplanetary magnetic field vector. It is shown that the energetic storm particles do not suffer any significant trapping in the magnetic regime associated with the onset of the Forbush decrease. It is shown that the various facts are consistent with the Parker ‘blast wave’ model for the interplanetary magnetic field associated with the Forbush decrease, while the Gold ‘magnetic bottle’ model is unable to explain the observed temporal variations in the anisotropic character of the particle fluxes. Studies of the net particle flux moving radially away from the sun suggest that the energetic storm particles are suffering acceleration within the magnetic field (i.e. within the shock front) associated with the onset of the Forbush decrease. It is suggested that the recurrent low‐energy cosmic‐ray events observed by other workers might consist of energetic storm particles associated with recurrent Forbush decrease events.
In this Letter we summarize the more important features of three cosmic-ray flare effects that were observed during the first thirty days of the flight of the Pioneer 6 spacecraft. It has been found that the cosmic radiation flux of mean energy 13 Mev/nucleon exhibited an extremely anisotropic character throughout each flare effect, the anisotropy persisting for in excess of 48 hours during one event. Subsequent flare effects not discussed herein exhibited similar characteristics.The direction of the anisotropy has been observed to exhibit marked and abrupt changes, the maximum flux occasionally arriving from directions included within the hemisphere centered on the antisun. The data indicate that the cosmic radiation was flowing away from the sun along well-defined and intertwined filaments, the filaments being defined by a filamentary magnetic field structure embedded in the solar wind. The very great. persistence of the anisotropy indicates that the interplanetary field within these filaments was very well ordered, insofar as a 13-Mev proton was concerned, and that there was continual injection of cosmic rays into the filamentary interplanetary magnetic field over a period of at least 48 hours on one occasion. INSTRUMENTATIONThe GRCSW cosmic-ray detector has been described elsewhere [Bartley et al., 1966]; briefly, it records the cosmic-ray counting rates from the four mean directions shown in Figure 1, for energy windows 7.5-45, 45-90, and 150-350 Mev. The latter window records alpha particles or heavier nuclei alone. The lowest energy window, 7.5-45 Mev, while intended to record protons or heavier nuclei, will also detect electrons in the energy range 7.5-13 Mev.Very great care has been taken in the design of the detection system to ensure that the four directional counting rates for each energy window are strictly comparable, it being possible to detect anisotropies as small as one part in 10'. An 'omnidirectional' counting rate of all particles depositing • 7.5 Mev in a thick Thalliumdoped CsI scintillator is also recorded. In-flight calibration procedures are employed to verify the correct operation of the detector once every 4 hours. PIONEER 6 SYMPOSIUM
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