David H. E. MacMahon
A5046206184- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Space Science and Extraterrestrial Life
- Pulsars and Gravitational Waves Research
- Planetary Science and Exploration
- Antenna Design and Optimization
- Radio Wave Propagation Studies
- Astronomy and Astrophysical Research
- Electromagnetic Compatibility and Measurements
- Astro and Planetary Science
- Soil Moisture and Remote Sensing
- Astrophysical Phenomena and Observations
- Superconducting and THz Device Technology
- Stellar, planetary, and galactic studies
- Particle Accelerators and Free-Electron Lasers
- Millimeter-Wave Propagation and Modeling
- Advanced Wireless Communication Techniques
- Galaxies: Formation, Evolution, Phenomena
- Astronomical Observations and Instrumentation
- Gyrotron and Vacuum Electronics Research
- Digital Filter Design and Implementation
- Advanced Data Compression Techniques
- Optical measurement and interference techniques
- Particle Detector Development and Performance
University of California, Berkeley
2016-2025
Breakthrough
2022-2024
Brown University
2023
Breakthrough Institute
2022
National Radio Astronomy Observatory
2021
Central China Normal University
2019
The Hydrogen Epoch of Reionization Array (HERA) is a staged experiment to measure 21 cm emission from the primordial intergalactic medium (IGM) throughout cosmic reionization ($z=6-12$), and explore earlier epochs our Cosmic Dawn ($z\sim30$). During these epochs, early stars black holes heated ionized IGM, introducing fluctuations in emission. HERA designed characterize evolution power spectrum constrain timing morphology reionization, properties first galaxies, large-scale structure,...
In this paper, we report new limits on 21cm emission from cosmic reionization based a 135-day observing campaign with 64-element deployment of the Donald C. Backer Precision Array for Probing Epoch Reionization (PAPER) in South Africa. This work extends presented Parsons et al. (2014) more collecting area, longer period, improved redundancy-based calibration, optimal fringe-rate filtering, and power-spectral analysis using quadratic estimators. The result is $2\sigma$ upper limit...
Magnetic fields near the event horizon Astronomers have long sought to examine a black hole's horizon—the boundary around hole within which nothing can escape. Johnson et al. used sophisticated interferometry techniques combine data from millimeter-wavelength telescopes world. They measured polarization just outside of Sgr A*, supermassive at center our galaxy, Milky Way. The is signature ordered magnetic generated in accretion disk hole. results help explain how holes accrete gas and launch...
We present new constraints on the 21cm Epoch of Reionization (EoR) power spectrum derived from 3 months observing with a 32-antenna, dual-polarization deployment Donald C. Backer Precision Array for Probing (PAPER) in South Africa. In this paper, we demonstrate efficacy delay-spectrum approach to avoiding foregrounds, achieving over 8 orders magnitude foreground suppression (in $\textrm{mK}^2$). Combining procedure removing off-diagonal covariances arising instrumental systematics, achieve...
Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights data (∼36 hr integration) from Phase I Hydrogen Array (HERA). The show evidence for systematics that can be largely suppressed systematic models down to a dynamic range ∼10 9 respect peak foreground power. This yields 95% confidence limit <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi...
Abstract Recently, the Hydrogen Epoch of Reionization Array (HERA) has produced experiment’s first upper limits on power spectrum 21 cm fluctuations at z ∼ 8 and 10. Here, we use several independent theoretical models to infer constraints intergalactic medium (IGM) galaxies during epoch reionization from these limits. We find that IGM must have been heated above adiabatic-cooling threshold by 8, uncertainties about ionization radio background. Combining HERA with complementary observations...
Abstract We report the most sensitive upper limits to date on 21 cm epoch of reionization power spectrum using 94 nights observing with Phase I Hydrogen Epoch Reionization Array (HERA). Using similar analysis techniques as in previously reported limits, we find at 95% confidence that Δ 2 ( k = 0.34 h Mpc −1 ) ≤ 457 mK z 7.9 and 0.36 3496 10.4, an improvement by a factor 2.1 2.6, respectively. These are mostly consistent thermal noise over wide range after our data quality cuts, despite...
Abstract The search for radio technosignatures is an anomaly detection problem: Candidate signals represent needles of interest in the proverbial haystack radio-frequency interference (RFI). Current frameworks find enormity false-positive signals, especially large surveys, requiring manual follow-up to a sometimes prohibitive degree. Unsupervised learning provides algorithmic way winnow most anomalous from chaff, as well group together RFI that bear morphological similarities. We present...
The Large-aperture Experiment to Detect the Dark Age (LEDA) was designed detect predicted O(100) mK sky-averaged absorption of cosmic microwave background by hydrogen in neutral pre- and intergalactic medium just after cosmological Age. spectral signature would be associated with emergence a diffuse Lyα from starlight during 'Cosmic Dawn'. Recently, Bowman et al. have reported detection this feature, an unexpectedly large amplitude 530 mK, centred at 78 MHz. Verification result independent...
The Collaboration for Astronomy Signal Processing and Electronics Research (CASPER) has been working a decade to reduce the time cost of designing, building deploying new digital radio-astronomy instruments. Today, CASPER open-source technology powers over 45 scientific instruments worldwide, is used by scientists engineers at dozens academic institutions. In this paper, we catalog current offerings collaboration, past present built users developers. We describe ongoing state software...
We report on 230 GHz (1.3 mm) VLBI observations of M87 with the Event Horizon Telescope using antennas Mauna Kea in Hawaii, Mt. Graham Arizona and Cedar Flat California. For first time, we have acquired interferometric phase information through measurement closure triangle long baselines. Most measured phases are consistent 0$^{\circ}$ as expected by physically-motivated models for structure such jet accretion disk models. The brightness temperature event-horizon-scale is $\sim 1 \times...
Abstract This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometre pathfinder instrument, we also show number “case studies” that investigate systematics seen while system, which...
The epoch of reionization power spectrum is expected to evolve strongly with redshift, and it this variation cosmic history that will allow us begin place constraints on the physics reionization. primary obstacle measurement EoR bright foreground emission. We present an analysis observations from Donald C. Backer Precision Array for Probing Epoch Reionization (PAPER) telescope which new limits HI over redshift range $7.5<z<10.5$, extending previously published single results cover full...
The Breakthrough Listen Initiative is undertaking a comprehensive search for radio and optical signatures from extraterrestrial civilizations. An integral component of the project design implementation wide-bandwidth data recorder signal processing systems. capabilities these systems, particularly at frequencies, directly determine survey speed; further, given fixed observing time spectral coverage, they sensitivity as well. Here, we detail recording system deployed 100 m aperture Robert C....
Breakthrough Listen is the most comprehensive and sensitive search for extraterrestrial intelligence (SETI) to date, employing a collection of international observational facilities including both radio optical telescopes. During first three years program, thousands targets have been observed with Green Bank Telescope (GBT), Parkes Automated Planet Finder. At GBT Parkes, observations performed ranging from 700 MHz 26 GHz, raw data volumes averaging over 1PB / day. A pseudo-real time software...
We present constraints on both the kinetic temperature of intergalactic medium (IGM) at z=8.4, and models for heating IGM high-redshift with X-ray emission from first collapsed objects. These are derived using a semi-analytic method to explore new measurements 21 cm power spectrum Donald C. Backer Precision Array Probing Epoch Reionization (PAPER), which were presented in companion paper, Ali et al. (2015). Twenty-one spectra amplitudes hundreds mK^2 can be generically produced if is...
Abstract The Epoch of Reionization (EoR) is an uncharted era in our universe’s history during which the birth first stars and galaxies led to ionization neutral hydrogen intergalactic medium. There are many experiments investigating EoR by tracing 21 cm line hydrogen. Because this signal very faint difficult isolate, it crucial develop analysis techniques that maximize sensitivity suppress contaminants data. It also imperative understand trade-offs between different methods their effects on...
The Galactic Center black hole Sagittarius A* (Sgr A*) is a prime observing target for the Event Horizon Telescope (EHT), which can resolve 1.3 mm emission from this source on angular scales comparable to that of general relativistic shadow. Previous EHT observations have used visibility amplitudes infer morphology millimeter-wavelength emission. Potentially much richer information contained in phases. We report phase Sgr obtained with total 13 nights over 4 years. Closure phases, sum phases...
The Event Horizon Telescope (EHT) has recently delivered the first resolved images of M87*, supermassive black hole in center M87 galaxy. These were produced using 230 GHz observations performed 2017 April. Additional are required to investigate persistence primary image feature - a ring with azimuthal brightness asymmetry and quantify variability on event horizon scales. To address this need, we analyze M87* data collected prototype EHT arrays 2009, 2011, 2012, 2013. While these do not...
We present a study of internal reflection and cross coupling systematics in Phase I the Hydrogen Epoch Reionization Array (HERA). In companion paper, we outlined mathematical formalism for such presented algorithms modeling removing them from data. this work, apply these techniques to data HERA's first observing season as method demonstration. The show evidence that, without removal, would hinder detection 21 cm power spectrum targeted EoR line-of-sight modes range 0.2 < k_parallel 0.5\ h^-1...
Abstract We report results from very long baseline interferometric (VLBI) observations of the supermassive black hole in Galactic center, Sgr A*, at 1.3 mm (230 GHz). The were performed 2013 March using six VLBI stations Hawaii, California, Arizona, and Chile. Compared to earlier observations, addition APEX telescope Chile almost doubles longest length array, provides additional uv coverage N–S direction, leads a spatial resolution ∼30 μ as (∼3 Schwarzschild radii) for A*. source is detected...
Abstract We present limits on the 21 cm power spectrum from Epoch of Reionization using data 64 antenna configuration Donald C. Backer Precision Array for Probing (PAPER) analyzed through a pipeline independent previous PAPER analyses. Previously reported results have been found to contain significant signal loss. Several lossy steps pipelines not included in this analysis, namely delay-based foreground filtering, optimal fringe-rate and empirical covariance-based estimators. Steps that...
Abstract A line of sight toward the Galactic Center (GC) offers largest number potentially habitable systems any direction in sky. The Breakthrough Listen program is undertaking most sensitive and deepest targeted SETI surveys GC. Here, we outline our observing strategies with Robert C. Byrd Green Bank Telescope (GBT) Parkes telescope to conduct 600 hr deep observations across 0.7–93 GHz. We report preliminary results from survey for extraterrestrial intelligence (ETI) beacons 1–8 GHz 7.0...
A new generation of radio telescopes is achieving unprecedented levels sensitivity and resolution, as well increased agility field view, by employing high-performance digital signal-processing hardware to phase correlate signals from large numbers antennas. The computational demands these imaging systems scale in proportion BMN2, where B the signal bandwidth, M number independent beams, N specifications many arrays lead excess tens PetaOps per second. To meet this challenge, we have...