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Funding Secured for ASTRO-H Satellite

An artist's drawing of the ASTRO-H satellite. (Image courtesy of JAXA/NEC. Click for larger image.)

Just three months after the successful launch of the SLAC-built Large Area Telescope, another space-based instrument is in the works. Thanks to recent funding and approvals from the Japan Aerospace Exploration Agency and NASA, a U.S. science instrument will be launched aboard the ASTRO-H satellite.

The observatory, which JAXA plans to launch in 2013, will include several components: a soft X-ray spectrometer, a soft X-ray imager, a soft gamma-ray detector and two hard X-ray imagers. Together, these instruments will look at celestial X-ray sources and the properties of their emission. With their superb sensitivity to hard X-rays and unrivaled energy resolution in soft X-rays, these instruments will explore the most energetic phenomena in the universe, involving particles at energies that can't be readily produced in the laboratory.

The Soft Gamma-ray Detector, which will observe the highest energy range of the ASTRO-H instruments, will be built under a collaboration between JAXA and the Kavli Institute for Particle Astrophysics and Cosmology, under the guidance of SLAC physicist Hiroyasu Tajima. The SGD will provide the unprecedented and unique capability of measuring the polarization of celestial sources in soft gamma rays. "These polarization measurements will allow us to perform precise studies of the geometry of astrophysical sources," said Tajima.

"This is another example of technology that has been developed in a particle physics context finding application in other fields of physics," added KIPAC Director Roger Blandford.

The premier instrument on the spacecraft, the Soft X-ray Spectrometer, or SXS, is a low-temperature detector capable of very precise measurements of soft X-rays. It will very precisely probe the motion of matter in extreme environments and investigate the nature of dark matter on large scales by exploring how galaxies and clusters of galaxies form and evolve.

"SXS will open an area of science completely unexplored so far," said Blandford. "By performing detailed studies of clusters of galaxies, SXS will allow us to trace the evolution of structures in the universe."

The X-ray sensor and telescope for the SXS instrument will be fabricated at NASA's Goddard Space Flight Center, with funding secured via a proposal to NASA's highly competitive Explorers Program. The full SXS instrument will be constructed at JAXA.

Researchers have sought to fly detectors similar to SXS in the past, with each project ending in disappointment. Such an instrument was originally set to fly on the Chandra X-Ray Observatory, but was shed as a result of cost reductions. Then, in 2000, a spacecraft carrying a similar instrument crashed into the ocean after liftoff due to a malfunctioning booster rocket. In 2005, a satellite carrying another low-temperature X-ray detector successfully launched into space, but a defect in the cooling system made it inoperable.

"Despite its tragic history, there is still tremendous interest in the community to have such an instrument," said KIPAC scientist Greg Madejski, who serves on the scientific steering committee for the project. "SXS will offer something never before seen. Really, it's the only game for large, diffuse sources of celestial X-rays."

In addition to SXS, ASTRO-H will also carry two hard X-ray telescopes. These instruments will observe very high energy X-rays, which have been difficult to study precisely with previous instruments. By bouncing the X-rays off of a specially coated surface—a process often used in synchrotron facilities including the Stanford Synchrotron Radiation Laboratory—the hard X-ray instruments onboard ASTRO-H will observe faint objects in the universe in never-before-seen energies.

"Building on one of KIPAC and SLAC's core competencies, we will help answer some of the most fundamental questions that can't be answered with ground-based telescopes and particle detectors," said Madejski. "The observations from ASTRO-H will indirectly put strong constraints on particle physics, and will help us better understand the makings of the universe."

Funding for ASTRO-H has been provided by JAXA and NASA.

—Kelen Tuttle
SLAC Today, September 17, 2008