High energy gamma rays may emanate in the Milky Way (Forwarded)

Public Affairs Office
Los Alamos National Laboratory

Contact:
Todd Hanson (505) 665-2085

04-197

December 14, 2005

High energy gamma rays may emanate in the Milky Way

LOS ALAMOS, N.M. -- Los Alamos scientists, in collaboration with
researchers from nine institutions across the United States, have
evidence from the Laboratory's Milagro telescope that TeV (one trillion
electron volts) gamma rays, the most energetic form of electromagnetic
radiation known, can originate in the plane of the Milky Way galaxy. The
discovery is the first evidence of such high-energy gamma rays arising
from interactions of cosmic rays with matter in our galaxy.

In a paper published in today's Physical Review Letters, the team of
scientists explain how they have been able to determine an approximate
location of the gamma rays place of origin within the Milky Way based on
observations of the secondary, or air shower, particles that are
generated when gamma rays hit Earth's atmosphere. These air shower
particles are detected as they pass through the water in the
6-million-gallon pond that comprises the Milagro telescope and create a
phenomenon called Cerenkov radiation. This Cerenkov radiation produces
visible and ultraviolet photons that are detected by the telescope's 737
floating photon detectors. The gamma rays that enter the atmosphere are
the same as the photons that make up visible light, but are roughly one
trillion times more energetic than visible light.

According to Gus Sinnis, the Los Alamos astrophysicist in charge of the
Milagro telescope, "The gamma rays we observed at Milagro might very
well be particle fragments that were scattered across the galaxy when
even higher energy cosmic rays struck the matter distributed throughout
the Milky Way. These cosmic rays may, in turn, have come from a
collapsing star or a supermassive black hole."

With the ability to continuously monitor the entire Northern hemisphere
sky in the 1 TeV energy range, Milagro is the largest gamma ray detector
of its kind in the United States. The latest discovery is the result of
an analysis that isolated roughly 70,000 TeV gamma-ray events emanating
from within a region of the Milky Way plane out of roughly 150 billion
TeV-level events recorded by Milagro for the three years beginning in
July 2000.

In addition to researchers from Los Alamos, the Milagro Milky Way gamma
ray team includes researchers from George Mason University, New York
University, Michigan State University, the University of
California-Irvine, University of California-Santa Cruz, University of
Maryland-College Park, University of New Hampshire and the University of
Wisconsin.

The Milagro telescope has been in operation at the Laboratory's Fenton
Hill research site since 1998. The continuing operation of Milagro is
made possible by support from the National Science Foundation, the
Department of Energy's Office of Science, Los Alamos National Laboratory
and the University of California's Institute of Geophysics and Planetary
Physics.

Los Alamos National Laboratory is operated by the University of
California for the National Nuclear Security Administration of the U.S.
Department of Energy and works in partnership with NNSA's Sandia and
Lawrence Livermore national laboratories to support NNSA in its mission.
Los Alamos enhances global security by ensuring the safety and
reliability of the U.S. nuclear deterrent, developing technologies to
reduce threats from weapons of mass destruction, and solving problems
related to defense, energy, environment, infrastructure, health and
national security concerns.