Astrophysics 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.

EBEX

Amber Miller leads the Columbia University Experimental Cosmology group, dedicated to studying relic signatures from the Big Bang with the goal of understanding the origin and evolution of the universe. Specifically, the team studies the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich Effect (SZE) using sensitive centimeter and millimeter-wave instruments designed specifically for this work. The Columbia team designs, builds, deploys, and analyzes data from novel telescopes employing cutting edge technology, much of which is piloted and tested by the group. The QUIET and EBEX experiments - currently under development in close collaboration with teams at other universities - are designed to probe detailed physics in the universe when it was much less than one second old. The first QUIET camera, built at Columbia, is currently observing the CMB from 17,000 ft. in the Atacama desert in Chile. The EBEX experiment is currently being integrated at Columbia's Nevis laboratories for it's first flight from a high-altitude balloon in the spring of 2009.

Prof. Miller has also long held an interest in issues on the interface between science and policy. She worked at Princeton University on issues related to satellite verification of nuclear non-proliferation agreements, organized a round table meeting at Columbia with the Union of Concerned Scientists, and has participated in several conferences on science and politics. Prof. Miller developed and piloted a seminar at Columbia entitled "Science, Politics, and Critical Thinking", and taught a lecture course entitled "Weapons of Mass Destruction". She was a Columbia University Committee on Global Thought Fellow, and is currently a Term Member on the Council on Foreign Relations.

The E and B Experiment (EBEX) is a NASA-funded balloon-borne telescope designed to measure the polarization of  the cosmic microwave background (CMB). The experiment will use 1432 transition edge sensor (TES) bolometric detectors read out with a frequency multiplexed SQUID readout. EBEX will observe in three frequency bands centered at 150, 250, and 410 GHz, with 768, 384, and 280 detectors in each band, respectively. This broad frequency coverage will provide valuable information about foreground emission from thermal dust. The polarimetry and signal modulation are achieved using an achromatic half wave plate (AHWP) rotating on a superconducting magnetic bearing and a fixed wire grid polarizer. The 420 square degree observing area and 8' resolution provide sensitivity to an angular power spectrum from 0.2 deg to 5 deg. This will allow EBEX to observe the primordial B-mode signal predicted by inflation on scales of about 0.5 deg and the anticipated lensing B-mode signal at smaller angular scales. Simulations show that EBEX will detect the primordial B-mode signal if the tensor to scalar ratio, r, is 0.1, or it will reduce the current upper limit to ~0.05. The test flight took place in June, 2009, from Ft. Sumner, NM, and the science flight will occur over Antarctica.

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.

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.

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.

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.

VERITAS

Professor Reshmi Mukherjee (Barnard), Brian Humensky

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.

General CMB and SZE Science

As recent experiments such as the hugely successful WMAP satellite have demonstrated, the Cosmic Microwave Background (CMB) provides a clean laboratory for studying the physics of the early  Universe. Arguably the most exciting future CMB results will come from measurements of the CMB polarization signal.  CMB polarization is generated by the same density perturbations that give rise to temperature  anisotropies (E-mode polarization) and, in the inflationary universe scenario, by  distortions in the spacetime metric caused by inflationary gravity waves (producing a separable,  B-mode polarization signature). Measurements of E-mode polarization will allow us to break degeneracies in the determination of cosmological parameters present with temperature anisotropy measurements alone,  and improve cosmological constraints.  Measurements or limits placed on B-mode polarization will allow us to probe the very earliest moments of the history of the universe, verifying or refuting the inflationary paradigm.

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 SZA

The Sunyaev-Zeldovich Array (SZA) is an interferometer comprised of eight 3.5 m telescopes operating with two frequency bands, one centered at 30 GHz and onecentered at 90 GHz with a correlator bandwidth of 8 GHz. The combination of small telescopes optimized for SZE observations and large correlator bandwidth make this system roughly 100 times more sensitive than the previous SZE system on the OVRO (10.4m dishes) and BIMA (6.1m dishes) telescopes. The SZA has been used as a stand-alone instrument in two modes. In the first mode, using primarily 30 GHz receivers, a blank-field cluster survey was conducted. The second mode takesadvantage of the higher resolution possible for a given telescope configuration using both the 30 GHz and the 90 GHz receivers. In this mode detailed follow-up observations are made of specific clusters. The SZA is currently integrated withthe OVRO and BIMA arrays to form a single heterogeneous array known as CARMA, capable of imaging clusters to an angular resolution of 5".

QUIET

The Q U Imaging ExperimenT (QUIET) is a CMB Polarization experiment designed to exploit the development and deployment of a novel new array of coherent polarimeters. This work has been made possible by a breakthrough technology developed by Gaier and collaborators at JPL in which an entire polarimeter chain is fabricated in a compact module, clearing the path to production of large arrays of HEMT-based polarimeters. Our collaboration has built two cameras, one at 90 GHz (W-band) and one at 40 GHz (Q-band). The Columbia team to led the development,construction, and deployment of the 40 GHz camera, and is currently focused on analyzing the data. The W-band camera is currently in the field taking data.