UpDate - Vol. 11, No. 14, Page 3
December 12, 1991
Antarctic lab showers physicists with information

     Although they have never been to Antarctica, Thomas Gaisser,
professor of physics, and Todor Stanev, associate professor of
physics, both of the Bartol Research Institute, are conducting
research there, studying air showers of high energy particles,
which enter the atmosphere at nearly the speed of light.
     For their project, they are sharing a large outdoor laboratory
at the Amundsen-Scott South Pole Station with Alan Watson of Leeds
University in Great Britain. The project originated with Martin
Pomerantz, director emeritus of Bartol, who is a pioneer of
astrophysical investigations from the South Pole. The U.S. part of
the experiment is funded by the National Science Foundation.
     The astrophysicists are part of a team searching for air
showers from binary or double stars and other astrophysical objects
such as supernovas. Binary stars appear from a distance as a single
star, but are, in reality, two stars that are, astronomically
speaking, close to each other. Sometimes they are actually in
physical contact with each other.
     Such close binary stars interact, producing high energy
radiation, including X-rays, and possibly generate photons of such
high energy that they could make air showers when they strike the
atmosphere at Earth.
     Although you can't see them or feel them, and most people are
unaware of them, air showers are continually passing through the
atmosphere down to ground level. This subatomic bombardment is
caused by high energy protons and nuclei called cosmic rays
entering the atmosphere from all directions, Gaisser said.
     The incoming particles multiply in the atmosphere to produce
a pancake-shaped bunch of particles about the size of a football
field that flies through the atmosphere at nearly the speed of
light.
     The Bartol/Leeds team is searching for point sources of
unusual air shower activity, over and above the isotropic
background of cosmic ray showers.
     The South Pole was chosen as an observatory to look for
showers from celestial bodies or sources that are expected to emit
ultra-high energy radiation only sporadically, if at all. When
viewed from a pole of the Earth, astronomical objects do not rise
or set, but are always in view at the same elevation. Because of
this, any active phase of an astronomical body can be picked up.
     John Petrakis, a post-doctoral fellow at Bartol, is currently
at the South Pole working with Nigel Smith from Leeds and others,
installing a new data acquisition system for the experiment.
Graduate student John Van Stekelenborg has spent the previous two
austral summers tending the experiment and is now completing his
doctoral work at Bartol.
     There are 24 sensors at the South Pole to detect air showers.
These are housed in boxes about 100 feet from each other and 600
feet from the geographic South Pole. When high energy particles hit
the sensors, the amplitude, time and direction are recorded.
Scintillators flash, and the data is fed into the central computer,
located in a small hut. The only problem with the computer has been
static electricity, since grounding is impossible as the ice is
9,000 feet deep.
     The sensors are a form of a telescope, responding to air
shower energy instead of looking visually at celestial bodies."What
we are looking for is any unusual activity that might emanate from
an astronomical object, such as a binary star, Gaisser said. "For
example, in 1988, there was greater activity than normal from an
unseen source, possibly from a binary star, and then it ceased.
When this year's data arrives, we will search in the area of this
source to see if there was further activity "Because the South Pole
is out of reach of the normal network of communication satellites,
only small samples of data, less than 1 percent, can be transmitted
on a regular basis during the Antarctic winter, which runs from
February to the end of October. During this time, the South Pole
Station is almost totally cut off from the rest of the world,
except for a mid-winter air drop and connections by electronic mail
and ham radio.
     A scientist from Leeds left the Pole last month with the past
year's data, which was taken to Leeds and copied and then sent to
Bartol. It will be analyzed by both institutions.
     The astrophysicists from Delaware and Leeds meet several times
during the year to confer. For example, Watson has been on campus
this month to meet with his colleagues and to speak at the
Conference on Particle Acceleration in Cosmic Plasmas, hosted by
Bartol. "We are essentially doing high energy astronomy and
learning from each other," Gaisser said.
     Gaisser, who has a doctorate in physics from Brown University,
has authored a book, Cosmic Rays and Particle Physics.
                                        - Sue Swyers Moncure