Suzaku Explains Cosmic Powerhouses (Forwarded)

Robert Naeye
Goddard Space Flight Center, Md. December 20, 2007
301-286-4453

Suzaku Explains Cosmic Powerhouses

GREENBELT, Md. -- By working in synergy with a ground-based telescope array,
the joint Japanese Aerospace Exploration Agency (JAXA)/NASA Suzaku X-ray
observatory is shedding new light on some of the most energetic objects in
our galaxy, but objects that remain shrouded in mystery.

These cosmic powerhouses pour out vast amounts of energy, and they
accelerate particles to almost the speed of light. But very little is known
about these sources because they were discovered only recently.
"Understanding these objects is one of the most intriguing problems in
astrophysics," says Takayasu Anada of the Institute for Space and
Astronautical Science in Kanagawa, Japan. Anada is lead author of a paper
presented last week at a Suzaku science conference in San Diego, Calif.

These mysterious objects have been discovered in just the last few years by
an array of four European-built telescopes named the High Energy
Stereoscopic System (H.E.S.S.), located in the African nation of Namibia.
H.E.S.S. indirectly detects very-high-energy gamma rays from outer space.
These gamma rays are the highest-energy form of light ever detected from
beyond Earth, so H.E.S.S. and other similar arrays have opened up a new
branch of astronomy.

The gamma rays themselves are absorbed by gases high up in Earth's
atmosphere. But as the gamma rays interact with air molecules, they produce
subatomic particles that radiate a blue-colored light known as Cherenkov
radiation. H.E.S.S. detects this blue light, whose intensity and direction
reveals the energy and position of the gamma-ray source.

The H.E.S.S. observations were groundbreaking, but the array's images aren't
sharp enough to reveal the exact location where particles are being
accelerated or how the particles are being accelerated. To solve this
problem, several teams aimed Suzaku in the direction of some of these
H.E.S.S. sources. Any object capable of emitting high-energy gamma rays will
also produce X-rays, and Suzaku is particularly sensitive to high-energy
(hard) X-rays.

When Anada and his colleagues pointed Suzaku at a source known as HESS
J1837-069 (the numerals express the object's sky coordinates), the X-ray
spectrum closely resembled X-ray spectra of pulsar wind nebulae -- gaseous
clouds that are sculpted by winds blown off by collapsed stars known as
pulsars. Pulsar wind nebulae emit hard X-rays, and their X-ray output
remains relatively constant over long timescales. "The origin of the
gamma-ray emission from HESS J1837-069 remains unclear, but we suspect that
this source is a pulsar wind nebula from the Suzaku observation," says
Anada.

NASA's Chandra X-ray Observatory and the European Space Agency's XMM-Newton
X-ray Observatory have revealed that other H.E.S.S. sources are also pulsar
wind nebulae. These combined gamma-ray and X-ray observations are revealing
that pulsar wind nebulae are more common and more energetic than astronomers
had expected.

Another group, led by Hironori Matsumoto of the University of Kyoto in
Japan, targeted Suzaku on HESS J1614-518. This source belongs to a class of
objects known as "dark particle accelerators" because their ultrahigh
energies suggest they are accelerating particles to near-light speed,
turning them into cosmic rays. But what are these objects, and what kinds of
particles are being accelerated?

Although the nature of these objects remains a mystery, Suzaku's
observations do reveal the identity of the particles. When electrons are
accelerated to high speeds, they spiral around magnetic field lines that
permeate space, generating copious X-rays. But since protons are 2,000 times
more massive than electrons, they emit few X-rays. Matsumoto and his
colleagues reported at the conference that HESS J1614-518 is a very weak
X-ray emitter. "This result strongly suggests that high-energy protons are
being produced in this object," says Matsumoto.

Suzaku also observed two other H.E.S.S. dark particle accelerators, but
found no obvious X-ray counterparts at the H.E.S.S. positions. These sources
must also be weak X-ray emitters, indicating they are accelerating mostly
protons. As Matsumoto says, "Using the high sensitivity of the Suzaku
satellite, we can find strong candidates for the origin of cosmic rays."

Launched in 2005, Suzaku is the fifth in a series of Japanese satellites
devoted to studying celestial X-ray sources. Managed by JAXA, this mission
is a collaborative effort between Japanese universities and institutions and
NASA Goddard.

For related images to this story, please visit on the Web:
http://www.nasa.gov/centers/goddard/...werhouses.html