Experiments

BALLOON BORNE X-RAY HIGH-ENERGY FOCUSING TELESCOPE

Professor Charles Hailey
Currently we are building the telescopes for the High Energy Focusing Telescope (HEFT) experiment. HEFT will be the world’s largest hard X-ray telescope, operating in the 20-120 keV energy band and flown from a balloon. HEFT will map the hard X-ray emission from supernova remnants to investigate issues of stellar nucleosynthesis (through the mapping of radioactive Titanium) and study the origin and acceleration of cosmic-rays (through mapping the continuum hard X-rays produced in the same shocks that produce the cosmic-rays). HEFT employs a novel approach to the construction of low cost, high performance hard X-ray telescopes that was developed in our group. The first flight of HEFT will take place within a year with many flights to follow which will observe other objects of interest such as Active Galactic Nuclei. HEFT will also make the first high resolution hard X-ray maps of the galactic center, the site of many black holes and neutron stars. HEFT is being done in collaboration with several other institutions including CalTech detectors), Danish Space Research Institute (mirror coatings) and Lawrence Livermore National Lab (pointing system and gondola). We are also investigating the feasibility of employing the telescope fabrication techniques we have developed for HEFT to the next generation of X-ray satellites called Constellation-X (in collaboration with CalTech, Livermore, DSRI and Goddard Space Flight Center).

COSMIC MICROWAVE BACKGROUND (CMB)

Asst. Professor Amber Miller
A Columbia research effort in experimental CMB started in 2002 headed by Professor Miller. Miller studies anisotropies in the CMB, constraining cosmological parameters such as the geometry and composition of the Universe. She is also involved in the Interferometric Sunyaev-Zel'dovich Effect Imaging Experiment at the OVRO and BIMA radio observatories. The Sunyaev-Zel'dovich effect (SZE) causes a change in the apparent brightness of the CMB towards a cluster of galaxies or any other reservoir of hot plasma. Measurements of the effect provide distinctly different information about cluster properties than X-ray imaging data, while combining X-ray and Sunyaev-Zel'dovich effect data leads to new insights into cluster physics. The effect is redshift-independent, and so provides a unique probe of the structure of the Universe on the largest scales. The group will be designing instruments for non-targeted SZE surveys which will be capable of measuring all clusters independent of redshift out to a specified mass limit, providing a powerful probe of the high redshift Universe.

STACEE

Professor Reshmi Mukherjee (Barnard)
The Solar Tower Atmosphereic Cherenkov Effect Experiment (STACEE) is an experiment dedicated to the study of high energy light (gamma rays) produced in astrophysicical sources. We study gamma rays to learn how Nature's powerful accelerators work and to learn about possible new physics outside of our current theories. Astrophysical sources of gamma rays include powerful objects such as neutron stars, supernovae, and supermassive black holes. STACEE uses a large field of solar mirrors (heliostats) at the National Solar Thermal Test Facility near Albuquerque, NM. These mirrors were built for solar energy research conducted during the daytime. STACEE uses the mirrors at night for astronomy. The mirrors collect quick flashes of blue Cherenkov light that result from gamma-ray interactions in the atmosphere. The Cherenkov light is then detected and recorded by the STACEE equipment.

The National Solar Thermal Test Facility (NSTTF) is a national user facility for solar energy research. Its primary mission is to carry out research in the area of concentrated solar energy, but we are able to use this one-of-a-kind facility for astronomical research. The NSTTF is funded by the U.S. Department of Energy, and managed by Sandia National Laboratories.

LXeGRIT

Professor Elena Aprile
The Liquid Xenon Gamma-Ray Imaging Telescope (LXeGRIT) is a balloon-borne experiment which uses a liquid xenon time projection chamber (LXeTPC) to image gamma-ray emission from cosmic sources in the 0.15 -10 MeV energy band. The detector is the original prototype developed at Columbia to demonstrate gamma-ray spectroscopy and imaging in a homogeneous, 3D position sensitive LXeTPC with combined charge and light readout. To verify the application of this technology in space, the TPC was turned into a balloon-borne instrument, and tested in three flight campaigns,

from the Northern Hemisphere. Following the first engineering flight, of short duration, in 1997, LXeGRIT was successfully operated as gamma-ray telescope on two longer duration flights in 1999 and 2000. A total of about 36 hours of data have been accumulated with the LXeTPC at an average altitude of 39 km. The background rate measured in flight is consistent with that expected from the dominant flux of atmospheric gamma-rays, confirming the radiation hardness of Xe as detector material. The gamma-ray data from the strongest source in the sky, the Crab Nebula/Pulsar, in the 1 steredian field-of-view of LXeGRIT for more than 10 hours, are being analyzed to verify the response as Compton imager and polarimeter. LXeGRIT is a collaboration between Columbia, the University of New Hampshire, Waseda University in Japan and Padova University in Italy. The LXeGRIT balloon flight program and the continuuing R&D on xenon imaging detectors for future missions in highenergy astrophysics is supported by NASA. Back to Top

XENON - A Liquid Xenon Experiment for Dark Matter WIMPs

Professor Elena Aprile
XENON is a new experiment recently proposed to search for dark matter WIMPs through their elastic scattering in a liquid xenon target. With a projected sensitivity of 1 event/100 kg/year after 3 yr operation in an underground location, the experiment will probe the lowest SUSY parameter space. This sensitivity results from the combination of large mass, low detection threshold, low intrinsic background and excellent background discrimination power. The design uses an array of ten independent, self-shielded, three-dimensional position sensitive detector modules, each with an active Xe mass of 100 kg. The WIMP detection relies on the simultaneous ionization and scintillation signals produced in liquid xenon by a nuclear recoil. Currently the project is a collaboration between Columbia, Brown, Princeton and Rice University and LLNL. As of September 2002, a two-year R\&D phase for XENON has started, supported by a grant to Columbia by the National Science Foundation. Back to Top

GAPS - The Gaseous Antiparticle Spectrometer

Professor Charles Hailey
We have recently begun to investigate new methods to detect dark matter. We are studying a radically new concept which will search for weakly interacting massive particles (WIMPs) from satellites rather than underground. Our approach is called GAPS, the gaseous antiparticle spectrometer. GAPS relies on the detection of characteristic X-rays produced when antiparticles are captured into gas atoms in excited states and consequently decay. These X-rays uniquely define the mass of the captured particle. GAPS would search for antideuterons, which are produced in the annihilation of neutralinos, a type of WIMP predicted by supersymmetric theories. We are currently planning to test GAPS at laboratory accelerators, and these tests, if successful, will be followed by balloon and ultimately satellite experiments. Back to Top

LIGO Experimental Gravitational Wave Astrophysics

Asst. Professor Szabolcs Marka
The Experimental Gravity group at Columbia University (GECo) is dedicated to the advancement of the experimental gravitational wave science, with a special emphasis on astrophysical trigger based data analysis, detector characterization and timing studies.

The Laser Interferometer Gravitational-wave Observatories (LIGO) aim to detect gravitational waves by interferometrically monitoring the relative displacement of mirrors in response to space-time distortions. Originally postulated by Albert Einstein, gravitational waves shall carry unique and otherwise unobservable information about the universe. The current sensitivity of LIGO has already enabled us to put new limits on gravitational wave signals, although the direct detection of gravitational waves is still a future goal. The development of more sensitive advanced detectors is in progress, ensuring that the group will be in the frontline of gravity wave research for many years to come.

GECo’s efforts, competitively funded by the National Science Foundation and Columbia University, span from data analysis through detector characterization, to hands on experimental work with the detectors, thus offering talented students a diverse education and experience in the forefront of experimental research. Back to Top

VERITAS

Professor Reshmi Mukherjee (Barnard)
VERITAS (Very Energetic Radiation Imaging Telescope Array System) is a state of the art high energy gamma-ray observatory. The system, composed of four 12m diameter optical reflectors, each matched to a 500-pixel element camera, is designed to detect the flashes of blue light (Cherenkov radiation) that occur as a result of high energy gamma-ray interactions with the atmosphere. VERITAS is one of several observatories around the world aimed at learning more about the most violent, high energy phenomena in our universe. VERITAS will detect gamma rays at energies between 50 and 50,000 GeV with much greater sensitivity than any other telescope in the Northern Hemisphere. The observations with VERITAS will be a key to understanding many physical processes in nature.