Benbow, Wystan: Very High Energy Gamma-Ray Astronomy with VERITAS
Project Title: Very High Energy Gamma-Ray Astronomy with VERITAS
Project Advisor: Dr. Wystan Benbow, 617-496-7597, Observatory P-323, wbenbow@cfa.harvard.edu
Background: VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a stereoscopic array of four atmospheric-Cherenkov telescopes that are sensitive to very high energy (VHE; E> 100 GeV) gamma rays. Located at the F.L.Whipple Observatory in southern Arizona, USA, the array began operation in 2007, and is currently the most sensitive VHE observatory in the world. The VERITAS Collaboration, which consists of ~80 scientists from institutions in the U.S.A., Canada, Germany, and Ireland, is carrying out observations that cover a broad range of science topics. VERITAS seeks to both identify new sources of VHE gamma rays, and to perform in-depth studies (e.g. spectral, temporal and morphological measurements) of the known VHE sources to better understand their underlying fundamental processes. VERITAS continues to lead the emergent field of VHE gamma-ray astrophysics, where in the past twenty years the VHE source catalog has grown from ~10 to ~250 objects. VERITAS is a also keystone facility for the high-growth field of multi-messenger astrophysics.
Scientific Questions: What are the sources of high-energy neutrinos and gravitational waves? What is the population of extragalactic very high energy gamma-ray emitters? What are the underlying non-thermal mechanisms behind these powerful particle accelerators? How do supermassive black holes accrete matter and produce powerful jets? How do AGN jets accelerate particles and are they sources of ultra-high energy cosmic rays? What is the origin of, and the timescales of, the extreme variability observed in VHE gamma-ray emitting blazars?
Scientific Methodology: The SAO VERITAS group focuses on VHE observations of extragalactic objects including: active galactic nuclei (primarily blazars), radio galaxies, starburst galaxies, gamma-ray bursts and dark-matter dominated structures (e.g. galaxy clusters and dwarf galaxies). Since VHE gamma-ray sources emit radiation over ~20 orders of magnitude in energy, these studies often involve collaboration with experiments at lower energies (e.g., the Fermi Gamma-ray Space Telescope, several X-ray satellites (Chandra, Swift, NuSTAR, IXPE), and numerous optical and radio facilities). The multi-wavelength data are used to search for temporal flux correlations and variability time scales, and to generate spectral energy distributions enabling the non-thermal processes behind the observed emission to be modeled. Nearly every VERITAS observation also has multi-messenger astrophysics implications, and these science efforts also often involve correlation analyses of high-energy signals across all known astronomical messengers: photons, neutrinos, cosmic rays, and gravitational waves. A major goal of the SAO group is to publish the VERITAS AGN catalog, the first long-term, intensive multi-wavelength study of the entire (Northern) VHE AGN catalog, and an interpretation of these data. Members of the SAO group are expected to spend time at the VERITAS site observing and assisting with upgrades to various subsystems of the array, as well as in developing the next-generation of VHE gamma-ray instrumentation.
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Deluca, Ed: Solar Magnetic Field Modeling, Active Region Structure and Stability, Developing the Scientific Basis for Space Weather
Project Title: Solar Magnetic Field Modeling, Active Region Structure and Stability, Developing the Scientific Basis for Space Weather.
Project Advisor: Edward DeLuca, 617-496-7725, Observatory P136, edeluca@cfa.harvard.edu
Background: Sigmoidal active regions in the solar corona are a main source of coronal mass ejections and flares. Such regions are commonly observed by coronal imagers. This study will use observations from the Hinode X-ray Telescope (XRT) and the Solar Dynamics Observatory (SDO).
Scientific Questions: What is the magnetic structure and topology of sigmoids? Are flux rope topologies prevalent and what what are their parameters? Is flux cancellation the main mechanism for creating sigmoids? What magnetic instabilities are responsible for the eruption of sigmoids?
Scientific Methodology: This project considers both data of sigmoidal active regions observed with XRT and SDO, and magnetic field modeling. The Coronal Modeling System (CMS) will be used to model the regions. Development of new software may be necessary to accommodate the data analysis and modeling effort.
Doeleman, Sheperd: Imaging Supermassive Black Holes
Project Title: Imaging Supermassive Black Holes
Project Advisor: Dr. Sheperd Doeleman, 617-496-7762, Observatory M215, sdoeleman@cfa.harvard.edu
Background: The Event Horizon Telescope (EHT) is a Very Long Baseline Interferometry (VLBI) array operating at the shortest possible wavelengths, which can resolve the event horizons of the nearest supermassive black holes. Initial observations with the EHT have revealed Schwarzschild radius scale structure in SgrA*, the 4 million solar mass black hole at the Galactic Center, and in the much more luminous and massive black hole at the center of the giant elliptical galaxy M87. Over the next 2 years, this international project will add new sites and increase observing bandwidth to focus on astrophysics at the black hole boundary. The EHT will have an unprecedented combination of sensitivity and resolution with excellent prospects for imaging strong GR signatures near the horizon, detecting magnetic field structures through full polarization observations, time-resolving black hole orbits, testing GR, and modeling black hole accretion, outflow and jet production. In April 2017, the EHT team completed its first observing campaign with the potential for horizon imaging.
Scientific Questions: Our group is focusing on some of the most fundamental questions in astronomy that can only be answered with observations that resolve the event horizon of a black hole. How do black holes accrete matter? Simulations show that an interplay between magnetic fields and hot gas surrounding a black hole results in instabillities that drive matter to the event horizon, and the EHT will look for signatures of these physical processes. How do black holes launch jets that pierce entire galaxies? Some supermassive black holes power directed outflows that redistribute matter and energy on galactic scales, but the process is not well understood. By imaging the magnetic fields thought to accelerate charged particles at the black hole boundary, the EHT will test models for how jets are launched. Does General Relativity hold at the event horizon - was Einstein right? Close to the black hole, the strong gravity distorts light emitted by the infalling gas into a 'silhouette' or 'shadow'. The EHT is aiming to image this shadow whose shape and size is predicted by Einstein's Field Equations. Detection of this silhouette feature would confirm that millions of solar masses can be contained within a few Schwarzschild radii - all but cementing the existence of black holes. How does matter orbit black holes? Separate confirmation and testing of GR can be accomplished by time-resolving the orbits of material close to the black hole. The EHT can use non-imaging techniques to search for orbital signatures near the Innermost Stable Circular Orbit.
Scientific Methodology: Our group uses numerical simulations to refine imaging algorithms and tests of strong field GR near a black hole. We also develop cutting edge instrumentation that we bring to remote mountain tops and install at mm and submm wavelength observatories. Each site has an atomic clock that enables us to synchronize and compare recordings made at sites around the Globe, each observing the same black hole at the same time. This technique, known as VLBI, synthesizes a virtual telescope as big as the Earth with unparalleled magnifying power. Students interested in instrumentation, signal processing algorithms and black hole astrophysics will find a lot to do in this project.
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Drake, Jeremy: High Energy Stellar Physics
Project Title: High Energy Stellar Physics
Project Advisor: Dr. Jeremy J. Drake, 617-496-7850, Observatory B-441, jdrake@cfa.harvard.edu
Background: Stars exhibit a range of energetic phenomena: hot coronae found on young protostars and stars like the Sun accretion thermal radiation from hot white dwarfs, novae and neutron stars. These phenomena are all characterised by plasmas that radiate copiously in the X-ray range and can be studied with satellite observatories above the Earths atmosphere.
Scientific Questions: What heats the coronae of stars? How do stellar outer atmospheric phenomena affect stellar and planetary evolution - star formation itself, protoplanetary disks, angular momentum loss through stellar winds and mass ejections, and the evolution of binary systems? What is the nature of the outer layers of neutron stars? What is happening in violent novae explosions?
Scientific Methodology: Our studies have recently concentrated on X-ray observations of stars using the Chandra and XMM-Newton observatories, and multi-dimensional photoionisation and radiative transfer models of protoplanetarty disks. High resolution X-ray diffraction grating spectra provide detailed information on individual objects, whereas CCD imaging spectroscopy provides lower resolution information on larger samples of objects, such as young pre-main sequence star clusters. Other observations compliment these studies for example, optical high resolution spectroscopy has been used to obtain information on elemental abundances that are of interest for probing outer atmospheric abundance anomalies in stars. Protoplanetary disk models are employed to investigate disk structure and ionisation under the influence of energetic phenomena.
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Elvis, Martin: Astronomical Prospecting: Steps to Asteroid Mining
Project Title: Astronomical Prospecting: Steps to Asteroid Mining
Project Advisor: Dr. Martin Elvis, 617-495-7442, Observatory B-424, melvis@cfa.harvard.edu
Background: Asteroids number in the millions and the total mass of industrially useful raw materials they contain is far vaster than the accessible materials in the Earth's crust. There are many potentially ore-bearing asteroids, but as a fraction of the total they are quite rare. As a result asteroid mining is likely to proceed in a multi-step process, like terrestrial mining, from initial surveys to final extraction. Astronomical techniques must be the first step in prospecting the asteroids.
Scientific Questions: How can we identify potential ore-bodes among the many asteroids given that most are just "dumb rock"? We are investigating two approaches: (1) Remote prospecting via large astronomical telescopes are preferred as they are cheap and can prospect large numbers of asteroids rapidly. However the information returned is limited. (2) Proximity prospecting, using instruments on spacecraft within a kilometer or so of the asteroid, provides far more detailed information, if the right instruments are used. But this approach is expensive to apply to many asteroids.
Scientific Methodology: (1) for telescopic prospecting we are beginning a campaign with the PISCO instrument on a 6.5m Magellan telescope in Chile; PISCO takes 4-color images simultaneously, and gets high signal-to-noise in 2 minutes, allowing both spectral types and accurate orbits to be obtained from the same data. (2) CfA scientists have developed miniature X-ray optics and radiation hard X-ray sensors that will make great proximity prospecting tools as well as enabling X-ray navigation for deep space missions; we are developing these into a system and will propose it at every opportunity.
Papers related to this project:
(1) Elvis, M., 2016, "Astronomical Prospecting: A Necessary Precursor to Asteroid Mining", 66th International Astronautical Congress, IAC-15-D4.3.10.
(2) Galache J.L., Beeson, C.L., McLeod, K.K., and Elvis, M., 2015, "The need for speed in Near-Earth Asteroid characterization", Planetary and Space Science, Volume 111, p. 155-166.
Golub, Leon: Dynamics of the Solar Corona
Project Title: Dynamics of the Solar Corona
Project Advisor: Dr. L. Golub, 617-495-7177, Observatory P-132, lgolub@cfa.harvard.edu,
Background: Hot, X-ray emitting plasmas are ubiquitous throughout astrophysics, and the mechanism(s) responsible for their heating is poorly understood.
Scientific Questions: What causes the heating and dynamics of the hot, magnetized solar outer atmosphere? What combinations of observations and modeling can be carried out to determine the mechanisms involved?
Scientific Methodology: A combination of theory, modelling and experiment: calculate the plasma properties resulting from proposed instability mechanisms, model the observable effects, and compare to observations of the solar corona.
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Golub, Leon: Heating of Hot Magnetized Plasmas
Project Title: Heating of Hot Magnetized Plasmas
Project Advisor: Dr. L. Golub
Background: Hot, X-ray emitting plasmas are ubiquitous throughout astrophysics, and the mechanism(s) responsible for their heating is poorly understood.
Scientific Questions: What are the observable consequences of the different mechanisms proposed for heating of the solar coronal plasma? Can we distinguish among them via direct observation?
Scientific Methodology: A combination of theory, modelling and experiment: calculate the plasma properties resulting from proposed dissipation mechanisms, model the observable effects, and compare to observations of the solar corona.
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Green, Paul: Spectroscopic Variability of Quasars
Project Title: Spectroscopic Variability of Quasars
Project Advisor: Paul J. Green
Background: The physics of supermassive black hole accretion is rather poorly understood, but I use both multi-wavelength properties and variability to study the near-nuclear environment.
Scientific Questions: What does photometric variability tell us about the size of the quasar accretion disk, and how disturbances propagate? How do the broad emission lines change in response? Is the rare, strongestvariability seen in "Changing Look Quasars" a different phenomenon, or just the tail of the quasar variability distribution? What is the quasar duty cycle, and can they turn completely off and on again?
Scientific Methodology: Our study of the spectroscopic variability of quasars probes both long and short-term optical variability in quasars, tracing changes in the power-law continuum and corresponding changes in the broad emission lines. The primary scientific goal is to understand the surprisingly rapid and significant variability of Changing Look Quasars, using optical spectroscopy, optical photometry (from either existing surveys or dedicated follow-up observing programs), and X-ray observations. The primary dataset is the Time Domain Spectroscopic Survey (TDSS) of SDSS-IV, which will be expanded in SDSS-V under the Black Hole Mapper (BHM) program.
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McCarthy, Michael: Laboratory Spectroscopy of Highly-Reactive Molecules of Astrophysical Interest
Project Title: Laboratory Spectroscopy of Highly-Reactive Molecules of Astrophysical Interest
Project Advisor: Michael C. McCarthy, 617-495-7262 or 617-495-9848, P-256, mmccarthy@cfa.harvard.edu
Background: Understanding the chemical composition in the interstellar medium can provide much insight into a variety of astrophysical processes, allowing one to derive important physical properties such as mass loss, temperature, density, fractional ionization, etc. Many of the key chemical intermediates found in space are highly reactive or unstable species, generally unknown or unfamiliar on Earth, such as radicals, carbenes, and positively and negatively-charged ions. Unambiguous astronomical detection of these reactive intermediates frequently requires highly accurate measurements of their rotational spectra throughout the radio band. Using highly sensitive laboratory instrumentation and production techniques developed at SAO, such measurements are undertaken, yielding precisely rest frequencies to guide dedicated radio astronomical searches for new molecules.
Scientific Questions: What are the key chemical intermediates in astronomical sources? What methods and techniques can be used to detect this species in the laboratory? How can these intermediates be used to provide new insight into astrophysical process?
Scientific Methodology: Chemically unstable molecules of astronomical interest are produced and detected in the radio band using custom instrumentation. Laboratory searches are often undertaken in collaboration with leading theoretical groups here and abroad because computational predictions serve as a useful guide to experiment. Target reactive species are synthesized by applying an electrical discharge to a mixture of precursor gases, as the gas mixture rapidly expands to form an ultra-cold molecular beam. Fourier transform microwave spectroscopy is used in the centimeter-wave band to conduct spectral surveys at frequencies predicted by theory. Follow-up investigations to confirm the carrier of the rotational lines or to extend the frequency range of the laboratory measurements are often undertaken as part of this effort.
McCollough, Michael: A Multi-Wavelength Study of the Relativistic Jet Source Cygnus X-3
Project Title: A Multi-Wavelength Study of the Relativistic Jet Source Cygnus X-3
Project Advisor: Dr. Michael L. McCollough, 617-496-2119, Observatory B-240, mmccollough@cfa.harvard.edu
Background: Cygnus X-3 is one of the most enigmatic X-ray binaries to have been studied. Its X-ray flux shows a 4.79 hr modulation associated with its orbital period. While the period is typical of a low mass system IR observations have shown that the mass donating companion is a massive Wolf-Rayet star. Cygnus X-3 has two major X-ray states (low/hard and high/soft), shows correlative activity between the radio and hard X-ray, and relativistic jets have been observed in the system (~0.9c).
Scientific Questions: Among the issues we are seeking to address in this study are:
Hard X-Ray/Gamma-Ray Continuum: We seek to understand the nature of the hard X-ray/gamma-Ray continuum associated with major radio flares. Is it due to synchrotron or inverse Compton? Are the processes producing this emission nonthermal or thermal in nature?
Annihilation Lines: The major radio flares in Cygnus X-3 have been linked to relativistic jets. The composition of these jets is a major point of interest. Are they a pair plasma (electrons and positrons) or do baryons play major role in their makeup? The detection of annihilation lines make help answer this question.
Timing Properties: Do the major flares have a distinctive timing signature? The RXTE observations probe times very close to the creation of these major flares.
Properties of Cygnus X-3's Wind: The Chandra observations (supported by the RXTE) observations will allow a detailed (phased resolved) measurement of the parameters and nature of the wind associated with Cygnus X-3.
Multi-Wavelength Correlations: We will look for and study the correlations between the different wavelenghts (radio, X-ray, Gamma-Ray, IR). These will be examined relative to previously discovered correlations.
Scientific Methodology: Since early 2002 Cygnus X-3 had been in an unusually long quiescent state (~ 1300 days). At the start of 2006 Cygnus X-3 transitioned from a radio quiescent (low/hard) state to a flaring (high/soft) state. Among the activities that have been observed are an extended quenched state (high X-ray, very low radio, and very low hard X-ray emission), rapid (< 1 day) bright flares (~ 3 Jy), and three major radio flares (~ 14 Jy).
During this active state, a major international multi-wavelength observing campaign has been undertaken. This campaign includes observations in the radio (Ryle, RATAN-600), IR (PAIRITEL), UV/Optical (Swift), X-ray (Chandra, RXTE, INTEGRAL, Swift), hard X-ray (RXTE, INTEGRAL, Swift), and Gamma-ray (INTEGRAL, Whipple).
This project involves the analysis of these various data sets with particular emphasis on the spacecraft data (Chandra, INTEGRAL, RXTE, and Swift). We will be using XSPEC, FTOOLS, CIAO, and OSA (INTEGRAL Data Analysis) software to analyze the various data sets.
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Randall, Scott: The Structure and Physics of Galaxy Clusters
Project Title: The Structure and Physics of Galaxy Clusters
Project Advisor: Dr. Scott Randall, 617-496-7738, Observatory B-418, srandall@cfa.harvard.edu
Background: Clusters of galaxies are the largest gravitationally bound structures in the Universe. As such, they are excellent signposts for the study of cosmology and the growth of large scale structure. Galaxy clusters contain a hot, X-ray emitting atmosphere of plasma called the intracluster medium (ICM). There is an apparent negative feedback loop between outbursts of a cluster's central supermassive black hole (SMBH) and the ICM, although the details of this interaction are not fully understood. Radio observation reveal that clusters sometimes contain diffuse radio structures, such as radio halos, relics, and phoenixes. It is believed that cluster mergers power the formation of these radio structures, but here too the detailed physics is unclear. Multiwavelength observations of merging clusters can also, in some cases, allow constraints to be placed on the nature of dark matter. On larger scales, clusters connect with the cosmic web in their outskirts, where observations are challenging due to the low density and surface brightness of the ICM. Understanding the physics of the ICM is important for the use of clusters in cosmological studies, and has implications for galaxy evolution, plasma physics, accretion physics, and the growth of supermassive black holes.
Scientific Questions: What physical processes are at work in the low-density ICM at the outskirts of galaxy clusters, where the ICM interfaces with the cosmic web? How do connecting large scale structure filaments affect the ICM in cluster outskirts? How, in detail, is the negative feedback loop established between the central SMBH and the ICM? Is the amount and distribution of cold molecular gas consistent with a model where gas condenses out of the ICM and feeds the central SMBH? What can merging clusters tell us about the self-interaction cross section of dark matter particles? What is the nature of the diffuse radio structures seen in some merging clusters?
Scientific Methodology: This work will focus on using multiwavelength observations (with a focus on X-ray observations) and other techniques to study multiple aspects of galaxy cluster physics. Submillimeter observations (e.g., with ALMA) map the cool molecular gas in the cores of clusters, which is thought to feed their central supermassive black holes and establish a negative feedback loop by heating the surrounding hot, X-ray emitting ICM. X-ray and radio observations reveal the connection between physical processes in the ICM and diffuse radio sources. Constraints can be placed on the self-interaction cross section of dark matter, by comparing the offsets between the diffuse gas (X-ray), galaxy number density (optical), and total mass (optical lensing) peaks with results from numerical simulations. Finally, X-ray observations of the outskirts of clusters allow us to study the physics of the virialization region, where the ICM connects to the large scale cosmic web. A comparison with mock observations from state of the art hydrodynamical cosmological simulations will test our predictions in this region.
Reeves, Kathy: Plasma Heating and Energy Partition in Solar Flares and Coronal Mass Ejections
Project Title: Plasma Heating and Energy Partition in Solar Flares and Coronal Mass Ejections
Project Advisor: Kathy Reeves, 617-496-7563, Observatory P141, kreeves@cfa.harvard.edu
Background: Solar eruptions, in the form of solar flares and coronal mass ejections (CMEs), are the largest energy release events in the solar system and the main driver of space-weather disturbances at Earth. It is widely accepted that magnetic reconnection is the main process that enables the release of magnetic energy in solar eruptions. However, the details of the associated energy transfer into thermal and kinetic energy, and of the associated heating and distribution of plasma are still poorly understood.
Scientific Questions: What are the physical mechanisms that heat plasma during the impulsive phase of solar flares? How is the released energy partitioned? What are the physical mechanisms responsible for heating plasma in the region of the current sheet in the late phase of solar flares? How are supra-arcade plasma sheets formed? How are the recently discovered hot plasma channels formed and heated to temperatures of more than 10 MK in the early stages of an eruption? How is plasma in coronal mass ejections heated during an eruption, and how does it evolve?
Scientific Methodology: We will, for the first time, analyze energy transfer and plasma heating and evolution using state-of-the-art, fully thermodynamic, magnetohydrodynamic simulations of solar flares and coronal mass ejections. The simulations we will analyze are produced with the Magnetohydrodynamic Algorithm outside a Sphere (MAS) code, developed and maintained by Predictive Science Inc. (PSI). We will complement our numerical investigations with detailed analysis of high-cadence and high-resolution observations from current spacecraft, such as the Atmospheric Imaging Assembly instrument on the Solar Dynamics Observatory mission.
Stark, Antony: The South Pole Telescope (SPT)
Project Title: The South Pole Telescope (SPT)
Project Advisor: Antony Stark, 617-495-7256, Observatory M-205, astark@cfa.harvard.edu
Background: The SPT is a 10m diameter millimeter wave telescope located at Amundsen-Scott South Pole Station in Antarctica. It has been in continual operation since 2007, resulting in over 40 major publications on a variety of topics that are fundamental to cosmology and high-redshift astrophysics. SPT is operated by an informal consortium of 70 scientists from 20 institutions including the Harvard-Smithsonian Center for Astrophysics. CfA astronomer Antony A. Stark, as one of the founders of the project, can provide unrestricted access to all SPT consortium data. The project is manpower limited, with a great many interesting projects available to pre-doctoral students. Consortium policy is to encourage independent work by students and to reward those efforts with first-authorships.
Scientific Questions: SPT science falls into three broad categories: cosmology by direct observation of features in the Cosmic Microwave Background including E- and B-mode polarization and lensing; cosmology and astrophysics of galaxy clusters discovered via the Sunyev-Zeldovich effect; and the astrophysics of highly-redshifted galaxies that happen to be unusually bright because they are behind a strong gravitational lens. The SPT is among the few instruments in the world that is currently constraining cosmological models and the properties of neutrinos. Future observations will determine the tensor-scalar ratio, running, kinetic S-Z effect, the structure of matter between z = 0 and z = 1000, the timescale of reionization, the number and masses of neutrino species, and the history of Dark Energy. Galaxy cluster projects will study the ensemble of clusters in the context of cosmology as well as the physics of intergalactic gas, star formation and populations of stars in cluster galaxies. Our sample of highly-magnified high-z galaxies allow study of star and galaxy formation in the very early Universe. That data can be used, for example, to study the possible existence of a large-scale gradient in the fine structure constant.
Scientific Methodology: The SPT is engaged in several long-term survey projects to produce deep (~ 3 microK rms) images of 10% of the sky near the south galactic pole at 90, 150, and 230 GHz. Six years of data, comprising the first Sunyaev-Zeldovich effect survey and the first two deep polarization surveys are complete. Survey work is expected to continue for at least the next 5 years. The sensitivity of the SPT has recently been greatly improved with the successful commissioning of the SPT3G detector system. SPT is by far the most sensitive CMB instrument, currently operating at brightness levels 30X deeper than Planck at 3X higher resolution. Detections in the survey are followed up with a wide variety of observations in the radio, infrared, visual, UV and X-ray. Harvard-Smithsonian participants in this project routinely observe with the Hubble, Spitzer, and Chandra Space Telescopes, the Magellan, Gemini, and VLT telescopes, and the ALMA and ATCA radio telescopes.
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Tong, Edward: Next Generation Instrumentation for the Submillimeter Array
Project Title: Next Generation Instrumentation for the Submillimeter Array
Project Advisor: Edward Tong, 617-496-7641, etong@cfa.harvard.edu
Background: The Submillimeter Array (SMA) is an 8-element radio interferometer on Mauna Kea, Hawaii, operating at submillimeter wavelengths. The array is a pioneer in wideband radio interferometry. For our second generation instrumentation, wSMA, that we are currently developing, the superconducting receiver, based on the Superconductor-Insulator-Superconductor (SIS) junction will deliver an intermediate frequency (IF) from near DC to close to 20 GHz for processing. In the future, further enhancements of performance are possible by moving to a dual-sideband (2SB) configuration, even wider IF bandwidth and parallel dual band operation.
Scientific Questions: The present SIS mixers used in SMA are fabricated on crystalline quartz. With the advent of mature silicon chip processing, one can envision that the SIS mixers can be made on silicon wafer and other functionality can be integrated on the same chip, for example, coupler for local oscillator injection, quadrature hybrid for 2SB mixers, and planar orthomode transducer. While the individual technology exists, the goal of integrating them remains aloof.
Scientific Methodology: The research starts with a basic understanding of the operation of SIS mixers and various submillimeter components used in submillimeter receivers. It is followed by investigation of various receiver components in silicon, and experimenting with different configurations that would lead to a compact and practical receiver.