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The BN/KL region in the Orion molecular cloud is an archetype for the study of the formation of stars much more massive than the Sun. This region contains luminous young stars and protostars but, like most star-forming regions, is difficult to study in detail because of the obscuring effects of dust and gas. Our basic expectations are shaped to some extent(More)
The image of the emission surrounding the black hole in the center of the Milky Way is predicted to exhibit the imprint of general relativistic (GR) effects, including the existence of a shadow feature and a photon ring of diameter ∼50 μas. Structure on these scales can be resolved by millimeter-wavelength very long baseline interferometry. However,(More)
Observations of radio signals from distant pulsars provide a valuable tool for investigation of interstellar turbulence. The time shapes of the signals are the result of pulse broadening by the fluctuating electron density in the interstellar medium. While the scaling of the shapes with the signal frequency is well understood, the observed anomalous scaling(More)
I calculate the statistics of correlation of two digitized noiselike signals: drawn from complex Gaussian distributions, sampled, quantized, correlated, and averaged. Averaged over many such samples, the correlation r approaches a Gaussian distribution. The mean and variance of r fully characterize the distribution of r. The mean corresponds to the(More)
Attaining the limit of sub-microarcsecond optical resolution will completely revolutionize fundamental astrometry by merging it with relativistic gravitational physics. Beyond the sub-microarcsecond threshold , one will meet in the sky a new population of physical phenomena caused by primordial gravitational waves from early universe and/or different(More)
We have made the first VLBI synthesis images of the H 2 O maser emission associated with the central engine of the Seyfert galaxy NGC 1068. Emission extends about ±300 km s −1 from the systemic velocity. Images with submilliarcsecond angular resolution show that the red-shifted emission lies along an arc to the northwest of the systemic emission. (The(More)
We describe the expected distribution of intensity for a scintillating source of finite size observed through a scattering medium, including systematic and instrumental effects. We describe measurements of the size of the Vela pulsar, using this technique. 1. Theoretical Background Waves from a pointlike source observed through a scattering medium will(More)
We present measurements of the size of the Vela pulsar in 3 gates across the pulse, from observations of the distribution of intensity. We calculate the effects on this distribution of noise in the observing system, and measure and remove it using observations of a strong continuum source. We also calculate and remove the expected effects of averaging in(More)
We report observational upper limits on the mass-energy of the cosmological gravitational-wave background, from limits on proper motions of quasars. Gravitational waves with periods longer than the time span of observations produce a simple pattern of apparent proper motions over the sky, composed primarily of second-order transverse vector spherical(More)