arXiv subjects

Robert Lehmensiek

Publications and source records attributed to Robert Lehmensiek.

5 recordsLinked to original sources

arXiv2026

The ngVLA Band-4 Water Vapor Radiometry Concept

The ngVLA has adopted a standalone system with a $\sim$~1.5 m diameter antenna and associated ambient temperature receiver and electronics at each antenna as its baseline design for water vapor radiometer (WVR). The WVR is intended to decrease calibration overheads for tropospheric phase correction for the high frequency bands (5 \& 6; 30.5-116 GHz) to levels lower than feasible with fast switched reference gain calibration. In this memo, we present an alternative concept utilizing the standard Band-4 science receivers and the main antennas. This would require the Band-4 feed to be placed between those of Bands 5 \& 6 resulting in a beam offset of 0.8 deg, similar to the beam size of the standalone 1.5 m antenna. The main benefits of the Band-4 WVR concept are: (1) sensing water vapor in a region more representative of the Band 5 \& 6 science beams in the lower layers of the troposphere, in the near-field of the 18 m antenna, than the 1.5 m antenna (2) significantly relaxing the stability requirements due to the lower receiver temperature of the standard Band-4 cryogenic receiver and (3) eliminating the procurement, deployment, and maintenance of a large number of standalone units. Given these advantages, it is recommended that the details and the pros and cons of Band-4 WVR implementation compared a standalone system be carefully considered.

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arXiv2025

Preliminary Baseline Antenna Design for the Black Hole Explorer (BHEX) Mission

The Black Hole Explorer (BHEX) mission extends the submillimeter Very-Long-Baseline Interferometry (VLBI) to space. The preliminary baseline design of a shaped axial-symmetric displaced-axis dual-reflector antenna for the BHEX is presented. The main goal of the antenna design optimization is to maximize aperture efficiency given the geometric and mechanical constraints of a space-borne antenna.

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arXiv2024

The Black Hole Explorer: Instrument System Overview

The Black Hole Explorer (BHEX) is a space very-long-baseline interferometry (VLBI) mission concept that is currently under development. BHEX will study supermassive black holes at unprecedented resolution, isolating the signature of the "photon ring" - light that has orbited the black hole before escaping - to probe physics at the edge of the observable universe. It will also measure black hole spins, study the energy extraction and acceleration mechanisms for black hole jets, and characterize the black hole mass distribution. BHEX achieves high angular resolution by joining with ground-based millimeter-wavelength VLBI arrays, extending the size, and therefore improving the angular resolution of the earthbound telescopes. Here we discuss the science instrument concept for BHEX. The science instrument for BHEX is a dual-band, coherent receiver system for 80-320 GHz, coupled to a 3.5-meter antenna. BHEX receiver front end will observe simultaneously with dual polarizations in two bands, one sampling 80-106 GHz and one sampling 240-320 GHz. An ultra-stable quartz oscillator provides the master frequency reference and ensures coherence for tens of seconds. To achieve the required sensitivity, the front end will instantaneously receive 32 GHz of frequency bandwidth, which will be digitized to 64 Gbits/sec of incompressible raw data. These data will be buffered and transmitted to the ground via laser data link, for correlation with data recorded simultaneously at radio telescopes on the ground. We describe the challenges associated with the instrument concept and the solutions that have been incorporated into the baseline design.

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arXiv2024

The Black Hole Explorer: Motivation and Vision

We present the Black Hole Explorer (BHEX), a mission that will produce the sharpest images in the history of astronomy by extending submillimeter Very-Long-Baseline Interferometry (VLBI) to space. BHEX will discover and measure the bright and narrow "photon ring" that is predicted to exist in images of black holes, produced from light that has orbited the black hole before escaping. This discovery will expose universal features of a black hole's spacetime that are distinct from the complex astrophysics of the emitting plasma, allowing the first direct measurements of a supermassive black hole's spin. In addition to studying the properties of the nearby supermassive black holes M87* and Sgr A*, BHEX will measure the properties of dozens of additional supermassive black holes, providing crucial insights into the processes that drive their creation and growth. BHEX will also connect these supermassive black holes to their relativistic jets, elucidating the power source for the brightest and most efficient engines in the universe. BHEX will address fundamental open questions in the physics and astrophysics of black holes that cannot be answered without submillimeter space VLBI. The mission is enabled by recent technological breakthroughs, including the development of ultra-high-speed downlink using laser communications, and it leverages billions of dollars of existing ground infrastructure. We present the motivation for BHEX, its science goals and associated requirements, and the pathway to launch within the next decade.

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arXiv2020

MID-Radio Telescope, Single Pixel Feed Packages for the Square Kilometre Array: An Overview

The Square Kilometre Array (SKA) project is an international effort to build the world s largest radio telescope, enabling science with unprecedented detail and survey speed. The project spans over a decade and is now at a mature stage, ready to enter the construction and integration phase. In the fully deployed state, the MID-Telescope consists of a 150-km diameter array of offset Gregorian antennas installed in the radio quiet zone of the Karoo desert (South Africa). Each antenna is equipped with three feed packages, that are precision positioned in the sub-reflector focus by a feed indexer platform. The total observational bandwidth (0.35-15.4GHz) is segmented into seven bands. Band 1 (0.35-1.05GHz) and Band 2 (0.95-1.76GHz) are implemented as individual feed packages. The remaining five bands (Bands 3, 4, 5a, 5b, and 6) are combined in a single feed package. Initially only Band 5a (4.6-8.5GHz) and Band 5b (8.3-15.4GHz) will be installed. This paper provides an overview of recent progress on design, test and integration of each feed package as well as project and science goals, timeline and path to construction.

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