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ON THIS PAGE: John E. Carlstrom | Juan I. Collar | James W. Cronin | Roger H. Hildebrand | Stephan Meyer | Dietrich Müller | Simon P. Swordy | Scott Wakely | Bruce D. Winstein

Experimental Astrophysics

The University of Chicago is a major center for interdisciplinary research in experimental astrophysics and cosmology. Members of the Department of Physics work in close collaboration with members of the the Department of Astronomy and Astrophysics. Research in experimental astrophysics is organized under the Enrico Fermi Institute. Groups that are involved in experimental astrophysics research include members of the Laboratory for Space Research (LASR) and the High Energy Physics group. The NSF-funded Center for Cosmological Physics organizes research, symposia, a visitors program, and education/outreach activities at the interface of phyiscs and astrophysics. Members of the department are active in several different areas including

  1. Studies of the cosmic microwave background radiation spectrum and anisotropy,
  2. Cosmic dust studies detect polarization in the far-infrared emission as a probe of magnetic field structure,
  3. Investigations of solar, magnetospheric, and heliospheric phenomena,
  4. High energy gamma-ray astrophysics,
  5. Studies of high energy emission from active galaxies, supernovae, and pulsars, and
  6. Studies of the origin of cosmic rays from the lowest to the highest possible energies.
  7. Direct searches for non-baryonic dark matter.

Experimental programs are developing new detectors for space-based experiments, balloon payloads, and ground based systems.

John E. Carlstrom

Ph.D., California/Berkeley, 1988.
Subramanyan Chandrasekhar Distinguished Service Professor, Dept. of Astronomy & Astrophysics, Dept. of Physics, Enrico Fermi Institute, and the College.
Director, Center for Astrophysical Research in Antarctica (CARA).
Experimental physics and astrophysics, star formation and cosmology, observation and new instrumentation.

Observational cosmology using new instruments to measure the primary anisotropy in the Cosmic Microwave Background (CMB) radiation and the Sunyaev-Zel'dovich Effect. Leader of the Degree Angular Scale Interferometer (DASI) project. DASI, a unique 13 element compact interferometric array located at the NSF Amundsen-Scott South Pole station, recently reported detection of the harmonic peaks in the CMB angular power spectrum. The new DASI data was used to set tight constraints on cosmological parameters, such as the curvature of the universe (1.04±0.06) and the fractional amounts of baryonic and cold dark matter. The results provide further support for Inflationary models for the origin of the universe. Current DASI observations are directed toward measuring the polarization of the CMB anisotropy.

Interferometric techniques are also used for detailed imaging of the CMB which has been scattered by hot gas associated with clusters of galaxies, the Sunyaev Zel'dovich effect (SZE). The intensity of the SZE for a cluster is independent of its distance making the SZE an ideal cosmological probe. Combining SZE measurements with x-ray observations allows an independent determination of the expansion history of the universe, as well as detailed information about these extremely large structures. A major expansion of this project, which includes building a dedicated six element array of telescopes, has recently been funded. The factor of 100 increase in imaging speed provided by the new array will enable a SZE survey of the high redshift universe over a region of roughly 12 square degrees.

Visit the Center for Astrophysical Research in Antarctica (CARA) and the Department of Astronomy and Astrophysics.

updated 5/2001

Juan I. Collar

Ph.D., University of South Carolina, 1992.
Assistant Prof., Dept. Physics, Enrico Fermi Inst., and the College.
Experimental physics, neutrino and astroparticle physics.

Professor Collar has a home page.

My main interest is in the development of new methods for the detection for hypothetical astroparticles (WIMPs, axions, magnetic monopoles, any yet-to-be-discovered component of cosmic rays that might constitute a fraction of the 'dark matter'). Evidently, this is all risky business but I am interested in both journey and destination: the extreme levels of sensitivity sought in some of these experiments force us in the field to devise new detection approaches and to try to stay aware of the latest advances in particle detector technology. It is all a very enjoyable challenge. I am also attracted to other exotica such as double-beta decay (as part of the MAJORANA collaboration) and some 'hard' problems in neutrino detection (coherent neutrino scattering, detection of the relic neutrino sea). I enjoy the condensed-matter aspects of detector development, in particular the area of interactions between radiation and matter. I get easily excited about cross-disciplinary endeavors and real-life applications of detectors that may otherwise be chasing ghost particles.

Together with collaborators at the Groupe de Physique des Solides (Universite Paris VII), University of Lisbon, and Pacific Northwest National Laboratory, I developed large-mass, low-background superheated droplet detectors (SDDs) dedicated to WIMP (Weakly Interacting Massive Particle) searches (The SIMPLE dark matter search). In Chicago I was able to start investigating the possibility of making large bubble chambers stable enough for the same purpose. Much progress has been made (the Chicagoland Observatory for Underground Particle Physics, COUPP, using CF3I as an optimal WIMP target). At CERN I am involved in CAST, a search for solar axions using a decommissioned LHC test magnet, an interesting astroparticle spin-off from the Large Hadron Collider effort. More recently we started work on the application of new detector technologies to neutrino detection via coherent nuclear scattering. A reactor experiment, sensitive for the first time to this interesting neutrino process, is expected to start in 2006.

updated 10/2006

James W. Cronin

Ph.D., Chicago, 1955.
University Professor Emeritus, Dept. of Physics, Dept. of Astronomy and Astrophysics, and Enrico Fermi Institute.
Experimental physics, particle physics, ultra-high energy gamma-ray astronomy.

James Cronin and University of Leeds professor Alan Watson lead an international project to study the nature and origin of rare but extremely powerful, high-energy (>1019 eV), cosmic rays that periodically bombard Earth. The project includes more than 250 scientists from nineteen nations.

The scientists will practice a new form of astronomy rooted in particle physics. Construction of the Pierre Auger Observatory, a giant detector array near the cities of Malargue and San Rafael in Argentina's Mendoza Province, will be completed by 2003, but researchers plan to begin observations as early as 2001. The site will contain 1600 particle detection stations 1.5 kilometers apart, arranged in a giant grid covering 3000 square kilometers, an area about the size of the state of Rhode Island. The Auger Project collaborators hope later to construct a complementary northern hemisphere observatory which, together with the southern observatory, would allow studies of cosmic rays from the entire sky.

  • Particle Astrophysics. B. Sadoulet and J. Cronin. Physics Today 53, 1991.
  • Search for Discrete Sources of 100 TeV Gamma Radiation. J.W. Cronin et al. Phys. Rev. D45, 4385, 1992.
  • A Northern Sky Survey for Astrophysical Point Sources of 100 TeV Gamma Radiation. T.A. McKay, et al. Astrophysical J. 417, 742, 1993.
  • Observation of the Shadows of the Moon and Sun Using 100 TeV Cosmic Rays. A. Borione, et al. Physical Review D49, 1171, 1994.
  • Cosmic Rays at the Energy Frontier. J. Cronin, T.K. Gaisser, S.P. Swordy. Scientific American 276, 1, 44, 1997.
  • Cosmic Rays: The Most Energetic Particles in the Universe. J.W. Cronin. Rev. Mod. Phys. 71, S165, 1999.
updated 4/2001

Hildebrand picture Roger H. Hildebrand

Ph.D., California, Berkeley, 1951.
Samuel K. Allison Distinguished Service Professor Emeritus, Dept. of Physics, Dept. of Astronomy & Astrophysics, Enrico Fermi Institute.
Experimental physics, infrared astronomy.

Polarimetry at far-infrared and submillimeter wavelengths provides maps of magnetic fields in interstellar clouds as projected on the sky. The degree of polarization in molecular clouds depends strongly on wavelength. The polarization spectrum reflects emission from dust components that have different temperatures due to differences in exposure to heat sources, or, in diffuse regions, due to differences in emissivities of distinct grain species.

A polarimeter, SHARP, built in collaboration with Giles Novak - now at Northwestern University - and with other former Chicago students and colleagues,- makes it possible to pursue these topics with considerably improved resolution and sensitivity, and with passbands at both 350 and 450 microns. An archive of our previous results at 60 and 100 microns and results from other instruments at 850 and 1200 microns provide data for the first far-infrared/submillimeter spectra.

Among the topics under investigation are 1) turbulence in molecular clouds; 2) fields in external galaxies; 3) fields in Bok globules; 4) wavelength of minimum polarization in molecular clouds (< 350 microns?, > 350?, variable-cloud to cloud?); and, using polarization spectra from WMAP, 5) nature of anomalous microwave emission.

  • The Determination of Cloud Masses and Dust Characteristics from Submillimeter Thermal Emission. R. H. Hildebrand. 1983, Q. J. R. Astron. Soc. 24, pp 267 - 282.
  • Magnetic Fields and Stardust. R. H. Hildebrand. 1988, Q. Jl. R. astr. Soc., 29, 327 - 351.
  • The Magnetic Field in the Dust Ring at the Center of the Galaxy. R. H. Hildebrand, D. P. Gonatas, S. R. Platt, X. D. Wu, J. A. Davidson, M. W. Werner, G. Novak, M.Morris. 1990, Astrophys. J., 362, 114 - 119.
  • The Far-Infrared Polarization Spectrum: First Results and Analysis. R. H. Hildebrand, J. L. Dotson, C.D.Dowell, D. A. Schleuning, and J. E. Vaillancourt. 1999, ApJ, 516: 834 - 842.
  • A Primer on Far-Infrared Polarimetry. R. H. Hildebrand, J. A. Davidson, J. L.Dotson, C. D. Dowell, G. Novak, and J. E. Vaillancourt. 2000, PASP, 112, 1215 - 1235. See Errata 2000, PASP, 112, 1620.
  • Polarization of FIR/SUB-mm Emission. Roger Hildebrand & Larry Kirby. In Astrophysics of Dust. ASP Conference Series. Vol. 309, Eds. Adolf N. Witt, Geoffrey C. Clayton, & Bruce T. Draine 2004, pp 515 - 527.
  • Improved Data Reduction for FIR/Sub-MM Polarimetry. L. Kirby, J. A. Davidson, J. L. Dotson, C. D. Dowell, & R. H. Hildebrand. 2005, PASP, 117, 991.
  • Summary: Astronomical Polarimetry. R. Hildebrand, in ASP Conference Series Vol. 343 Astronomical Polarimetry - Current Status and Future Directions, 2005, ed's. A. Adamson, C. Aspin, C. J. Davis, and Fujioshi. pp 515 - 526.
updated 10/2006

Stephan Meyer

Ph.D., Princeton, 1979.
Professor, Dept. of Astronomy & Astrophysics, Dept. of Physics, Enrico Fermi Institute, and the College.
Experimental astrophysics, infrared astrophysics, observational cosmology.

The TopHat experiment is a balloon-borne Cosmic Microwave Background (CMBR) anisotropy measurement designed to measure 5% of the sky in a region around the south celestial pole. The bolometric instrument has five channels sensitive to frequencies from 150 to 600 GHz. It is designed to have good rejection of galactic dust foreground emission and have sensitivity of about 25 muK RMS per 20 arcminute beam. To minimize systematic errors, the 1-M telescope is flown on top of a high altitude balloon in a circumpolar flight. This position permits observations at high elevation angle and with an extensive ground-screen with no strong sources high in the sky. The instrument is to fly in late December 1999 or January 2000 with a flight lasting about 10 days. With its sky coverage and sensitivity, the instrument will determine the shape of the CMBR anisotropy power spectrum in the region enveloping the predicted position of the first "Doppler Peak." The l-space resolution is high enough to easily resolve and measure the position and heights of the first two peaks in the power spectrum.

The Microwave Anisotropy Probe (MAP) satellite, scheduled to fly in December 2000, will measure the Cosmic Microwave Background Radiation (CMBR) aniostropy over the full sky in five frequency bands from 22 to 100 GHz. The angular resolution of the highest frequency is 12 arcminutes making the instrument sensitive to the CMBR angular power spectrum from l=2 to 500. Launched into an orbit that takes the satellite to the earth-sun L2 point, MAP will have extremely low systematic errors and with the complete sky coverage and sensitivity will answer many of the key cosmological questions of interest.

The Center for Astrophysical Research in Antarctica (CARA) is an NSF Science and Technology Center (STC) which began in February 1991. The center supports several astrophysical experiments, all based at the (South Pole Station, which have as a common thread the investigation of the evolution of astrophysical structure. The investigations range over scales from the measurement of the Cosmic Microwave Background Radiation (CMBR) anisotropy to measurements leading to a better understanding of star forming regions. The experiments are also related in that they all are made at centimeter to micron wavelengths which requires that they be carried out at a very cold dry site such as the South Pole. This is because the emission from water vapor in the atmosphere and the telescopes themselves limit the sensitivity for ground-based measurements in this spectral range. The experiments being carried out by CARA include: AST/RO, the Antarctic Submillimeter Telescope and Remote Observatory; Viper, a 2-M telescope optimized to observe the anisotropy of the CMBR and other low-surface brightness objects; Abu, a 1024 x 1024 element detector array; and the Degree Angular Scale Interferometer (DASI), an interferometric CMBR anisotropy experiment.

Visit the Department of Astronomy and Astrophysics.

updated 3/1999 or later

Dietrich Müller

Ph.D., Bonn, 1964.
Professor, Dept. of Physics, Enrico Fermi Institute, and the College.
Experimental physics, cosmic rays, high-energy astrophysics.

Our research in high energy astrophysics includes the following topics:

Origin of high energy cosmic rays. Particle acceleration is a ubiquitous process in nature that occurs in all astronomical settings, from the surface of the sun to exotic, distant galaxies. In our galaxy, shock fronts from supernova explosions appear to be the sites where cosmic rays are accelerated over a large range of energies. However, the details of these processes are still poorly understood, and at the highest energies, above 1015 eV, other and as yet unknown sources of cosmic rays must exist. We aim to obtain observational constraints on the various models proposed for the origin of cosmic ray particles through precise measurements of the elemental composition and energy spectra of the individual cosmic ray components. Based on a series of investigations on high-altitude balloons and on the Space Shuttle, we have constructed a new and very large instrument, TRACER, that uses transition radiation detectors to permit measurements in the presently unexplored energy region between 1014 and 1015 eV. This detector exhibits a large sensitive area of nearly 5m2, weighs about 3 tons, and is carried by stratospheric balloons above the earth's atmosphere at a height of nearly 40 km above ground. A first balloon flight was conducted in 1999, and a long-duration flight to circle the Northern Hemisphere for about two weeks will be launched in 2002. TRACER also serves as a prototype for an instrument that may become part of the ACCESS mission which is now under consideration by NASA. ACCESS will be the largest cosmic ray detector ever flown in space, and will be mounted on the International Space Station for a duration of 3-4 years.

Search for anti-particles in the cosmic rays. Positrons and anti-protons are the only antiparticle species detected thus far in the cosmic radiation. They are generated subsequent to nuclear interactions in interstellar space and therefore provide an interesting probe on the structure of the interstellar medium and on the propagation of particles through the galaxy. However, there might also be more exotic contributions to the observed intensities of these particles, for instance, from the decay of hypothetical dark matter particles. These issues are studied with a balloon borne detector system, the High-Energy Antimatter Telescope (HEAT), which includes a superconducting magnet spectrometer. This instrument has been successfully flown in 1994 and 1995 to measure the flux of positrons and electrons over a wide energy range. At present, a modified detector system is used for the observation of high-energy antiprotons in balloon flights in 2000 and 2001. This work is conducted jointly with Simon Swordy and collaborators at several other institutions.

Gamma-ray astronomy. A major frontier area in gamma ray astronomy is the region of high energies, from about 100 GeV to several thousand GeV. In this energy region, supernova remnants in our galaxy could be identified, demonstrating that these are indeed the sites where cosmic rays are generated, and exciting discoveries wait to be made with the observation of extragalactic objects. Detectors in space do not have sufficient sensitivity for these observations, but arrays of Cherenkov telescopes on the ground can observe the gamma-ray showers generated in the Earth's atmosphere. We participate in the construction of the VERITAS installation in Arizona which has just begun and should lead to a 7-telescope array in 3-4 years. This work is conducted jointly with Simon Swordy, and in collaboration with a number of institutions in the US and in Europe.

  • Performance of the HEAT Spectrometer for Cosmic Ray Electrons and Positrons. D. Müller (for the HEAT collaboration). Nucl. Instr. and Methods A367, 71, 1995.
  • Towards the Knee: Direct Measurements of the Cosmic-Ray Composition with Electronic Detectors. D. Müller, E. Diehl, F. Gahbauer, P. Meyer, S. Swordy. Adv. in Space Res. 19, 719, 1997.
  • Energy Spectra and Relative Abundances of Electrons and Positrons in the Galactic Cosmic Radiation. S.W. Barwick, J.J. Beatty, C.R. Bower, C. Chaput, S. Coutu, G. deNolfo, D. Ficenec, J. Knapp, D.M. Lowder, S. McKee, D. Müller, J.A. Musser, S.L. Nutter, E. Schneider, S.P. Swordy, G. Tarlé, A.D. Tomasch, E. Torbet. Ap. J. 498, 779, 1998.
  • Cosmic-Ray Positrons: Are there Primary Sources? S. Coutu, S.W. Barwick, J.J. Beatty, A. Bhattacharyya, C. R. Bower, C. Chaput, G. deNolfo, M.A. DuVernois, A. Labrador, S. McKee, D. Müller, J.A. Musser, S.L. Nutter, E. Schneider, S.P. Swordy, G. Tarlé, A. D. Tomasch, E. Torbet. Astropart. Phys. 11, 429, 1999.
  • Cosmic Ray Electrons and Positrons. D. Müller. Adv. in Space Res. (2001, in press).
  • Cosmic Rays beyond the Knee. D. Müller. In The Astrophysics of Galactic Cosmic Rays, Kluwer, 2001 (in press).
updated 5/2001

Simon P. Swordy

Ph.D., Bristol, 1979.
James Franck Professor, Dept. of Physics, Dept. of Astronomy & Astrophysics, Enrico Fermi Institute, and the College.
Experimental physics, cosmic rays, space physics.

Prof. Swordy's astroparticle group has a home page.

My research is directed to observations and analysis of high-energy radiation from space mainly through the following experimental efforts. I am involved with several projects to make measurements of high energy gamma rays and cosmic ray particles:

The VERITAS experiment (Very Energetic Radiation Imaging Telescope Array System) is a collaboration formed to build the next generation of atmospheric Cherenkov telescopes for gamma ray measurements in the TeV energy region. This is an an array of four 12m telescopes located near Tucson, Arizona. This new generation of gamma-ray detectors provides an increase in sensitivity of more than an order of magnitude compared to previous instruments. This instrument provides a unique view into the most energetic environments of our Universe while providing a host of new scientific opportunities. VERITAS can be used to directly search for direct evidence connecting supernova remnant sources to the origin of cosmic rays. VERITAS can also discover extra-galactic AGN Blazar objects out to redshifts of z~0.2. The interaction of TeV photons with intervening radiation fields in our universe can be used to investigate properties of early star and galaxy formation.

The CREAM experiment (Cosmic Ray Energetics And Mass) is a high altitude balloon experiment to directly measure cosmic ray composition using transition radiation and thin calorimetry. This experiment performed a record-breaking flight of over 40 days around the Antarctic continent in 2004-2005. The data from this experiment is at present under analysis, it is designed to measure the history of cosmic rays in the galaxy in the 100 GeV energy region for the first time.

  • A new search for primordial black hole evaporations using the Whipple gamma-ray telescope. E. Linton et al. (VERITAS collaboration). Journal of Cosmology and Astroparticle Physics 1, 13, 2006.
  • New Measurement of the Cosmic-Ray Positron Fraction from 5 to 15 GeV. Phys. Rev. Lett. 93, 241102, 2004.
  • VERITAS: the Very Energetic Radiation Imaging Telescope Array System. F. Krennrich et al. (VERITAS Collaboration). New Astronomy Reviews, 48, 345, 2004.
  • Cosmic-ray energetics and mass (CREAM) balloon project. E. Seo et al. (CREAM collaboration), Advances in Space Research. 33, 1777, 2004.
  • Cosmic Rays at the Energy Frontier. J. Cronin, T.K. Gaisser, S.P. Swordy. Scientific American 276, 1, 44, 1997.
  • Cosmic Antimatter. G. Tarlé and S.P. Swordy. Scientific American April 1998.
updated 10/2006

Scott Wakely

Ph.D., University of Minnesota, 1999.
Assistant Professor, Dept. of Physics, Enrico Fermi Institute, and the College.
Experimental physics, particle astrophysics, high-energy astrophysics.

My research spans a number of topics in the categories of experimental astroparticle physics and high-energy astrophysics. This includes several investigations into the nature and origin of very high energy (VHE) cosmic radiation, including gamma rays above 10 GeV and cosmic rays above 100 TeV. I am also interested in topics at the interface of cosmology and astroparticle physics, including studies of the propagation of VHE gamma rays through extragalactic photon fields. I currently am working on the following projects:

VERITAS - the Very Energetic Radiation Imaging Telescope Array System. This experiment comprises 4 12-meter imaging atmospheric Cerenkov telescopes designed to detect and measure gamma rays over an energy range of 50 GeV to 50 TeV. VERITAS is currently taking data while under construction in southern Arizona. Once complete in 2007, VERITAS will be the most sensitive instrument of its kind in the northern hemisphere for the investigation of gamma ray sources such as galactic supernova remnants and AGN.

TRICE - the Track-Imaging Cerenkov Detector. TRICE is a collaboration with Argonne National Laboratory to build a high-resolution imaging telescope for the measurement of Cerenkov light directly from heavy cosmic ray primaries in the atmosphere. This technique was originated at Chicago and the first measurements demonstrating the method were performed in 2006, allowing the determination of cosmic ray composition with unprecedented precision for a ground-based instrument. Additionally, the technology developed for this task will have direct applications for the next-generation of ground-based gamma ray instruments.

Balloon and Space-based Transition Radiation Detection. Transition radiation detectors provide perhaps the only feasible way to make detailed measurements of high-energy (E > 100 TeV) cosmic ray fluxes at the top of the atmosphere. The TRD group at Chicago, which includes Professors Muller and Swordy, has recently flown two successful Long-Duration Balloon missions at the South Pole with the TRACER and CREAM instruments. In addition to this, we are working on designs for a possible future space-based TRD mission called ACCESS. ACCESS will be the largest cosmic-ray detector ever flown in space, allowing it to investigate energies up to the so-called "knee" in the primary cosmic ray spectrum.

  • Spectrum of VHE Gamma-rays from the blazer 1ES 1959+650 during flaring activity in 2002, The VERITAS Collaboration, ApJ 621, 181 (2005)
  • TeV Gamma-Ray Observations of the Galactic Center, The VERITAS Collaboration, ApJL 608, 97 (2004)
  • Transition Radiation Response over Large Ranges of Lorentz Factor, S.P. Wakely, NIM A522 22 (2004)
  • Precision X-Ray Transition Radiation Detection, S.P. Wakely, Astroparticle Physics 18, 67 (2002)
  • Discovery of Spectral Variability of Mrk 421 at TeV Energies, The VERITAS Collaboration, ApJL 575, 9 (2002)
  • A high resolution method for measuring cosmic ray composition beyond 10-TeV, APh 15, 287 (2001)
updated 10/2006

 Bruce D. Winstein

See Prof. Winstein's entry under Experimental High Energy Physics.


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