Las Cumbres Observatory Global Telescope (LCOGT) is a young organization dedicated to time-domain observations at optical and (potentially) near-IR wavelengths. To this end, LCOGT is constructing a world-wide network of telescopes, including the two 2m Faulkes telescopes, as many as 17 x 1m telescopes, and as many as 23 x 40cm telescopes. These telescopes initially will be outfitted for imaging and (excepting the 40cm telescopes) spectroscopy at wavelengths between the atmospheric UV cutoff and the roughly 1-micron limit of silicon detectors. Since the first of LCOGT's 1m telescopes are now being deployed, we lay out here LCOGT's scientific goals and the requirements that these goals place on network architecture and performance, we summarize the network's present and projected level of development, and we describe our expected schedule for completing it. In the bulk of the paper, we describe in detail the technical approaches that we have adopted to attain the desired performance. In particular, we discuss our choices for the number and location of network sites, for the number and sizes of telescopes, for the specifications of the first generation of instruments, for the software that will schedule and control the network's telescopes and reduce and archive its data, and for the structure of the scientific and educational programs for which the network will provide observations.Comment: 59 pages, 9 figures, 4 tables. AAS Latex v5.2. Accepted for publication in Pub. Astr. Soc. Pacifi
Simulations are performed of steady, two-dimensional relativistic jets incorporating the effects of mass entrainment. The form used for the mass source is the stellar wind entrainment model of Komissarov. We present a detailed study of the dynamical effects of entraining 'cool' (thermally sub-relativistic) material into 'hot' (thermally relativistic) jets by performing a series of pertinent simulations with levels of stellar mass loss compatible with current models and typical stellar distributions for elliptical galaxies. Initially cool jets are shown to heat up as they entrain due to dissipation, whilst initially hot jets cool due to thermal dilution (i.e. the dissipation is not sufficient to heat the entrained material to the temperature of the main flow). All jets decelerate due to entrainment, some to sub-relativistic levels. Similarly, all jets show significantly greater opening angles than associated with adiabatic expansion. The dissipation associated with entrainment causes only modest loss of kinetic energy flux, and we show that relativistic jets are affected much less by dissipation than are classical flows. An explanation for the Fanaroff & Riley division of radio sources is suggested in terms of the initial jet temperature. All else being equal, initially hotter jets are shown to have lower energy fluxes than cooler flows, indicating that the former are more closely related to FR-I sources and the latter to FR-lls. This distinction is shown to be qualitatively compatible with inferred levels of deceleration in Mach number and Lorentz factor. An estimate of the surface brightness for the simulations is derived using a simple emissivity model. It is found that initially 'hot' jets often show a 'gap' in surface brightness similar to that observed on kiloparsec scales at the base of many FR-I sources.
Work in time-domain astronomy necessitates robust, automated data processing pipelines that operate in real time. We present the BANZAI pipeline which processes the thousands of science images produced across the Las Cumbres Observatory Global Telescope (LCOGT) network of robotic telescopes each night. BANZAI is designed to perform near real-time preview and end-of-night final processing for four types of optical CCD imagers on the three LCOGT telescope classes. It performs instrumental signature removal (bad pixel masking, bias and dark removal, flat-field correction), astrometric fitting and source catalog extraction. We discuss the design considerations for BANZAI, including testing, performance, and extensibility. BANZAI is integrated into the observatory infrastructure and fulfills two critical functions: (1) real-time data processing that delivers data to users quickly and (2) derive metrics from those data products to monitor the health of the telescope network. In the era of time-domain astronomy, to get from these observations to scientific results, we must be able to automatically reduce data with minimal human interaction, but still have insight into the data stream for quality control.
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