Beppo -- the Satellite, the Science, and the Man
BeppoSAX is the first X-ray mission (and, of the coming near-future
satellites, the only mission) which has the capability of observing sources
over more than three decades of energy - from 0.1 to 200 keV - with a
relatively large area, a good
energy
resolution, and
imaging
capabilities (resolution of about 1 arcminute) in the range of
0.1 - 10 keV. The instrument complement aboard the satellite consists of a
medium energy (1 - 10 keV)
concentrator/spectrometer, MECS; a low energy (0.1 - 10 keV)
concentrator/spectrometer, LECS; a high pressure gas scintillation proportional
counter (3 - 120 keV), HPGSPC; and a phoswich detector system (15 - 300 keV),
PDS. The anti-coincidence scintillator shields of the PDS is also used as a
gamma-ray burst monitor
in the range 100 - 600 keV.
Another important feature of BeppoSAX is its ability to monitor large
regions of the sky with a resolution of 5 arcminutes in the range 2 - 30 keV.
This will allow the study of long-term variability of sources down to 1 mCrab
(that's faint!) and, also, permit the detection of X-ray transient phenomena.
These capabilities are the result of two coded mask proportional counters
(Wide Field Cameras, WFC).
First Light on Cygnus X-1
BeppoSAX successfully performed its first scientific observation by
pointing
at the suspected
black hole
binary Cygnus X-1 from June 22 to 25. All of the instruments performed
nominally and showed that the source remains in its high state with a soft
spectrum in the
energy band 0.1-10 keV with an intensity of about 1 Crab. Below 10 keV, the
spectral shape is similar to that observed by Japanese X-ray satellite,
ASCA. A hard component
with a flux of about 0.3 Crab is visible in the energy range 10-300 keV. The
source intensity is variable, with a peak amplitude of about 40 percent at low
and high energies.
Credit: BeppoSAX/LECS Team at ESA/ESTEC |
The above image,
from the LECS, was obtained from a few hundred
seconds of
data during a real time ground station contact and shows Cyg X-1 close to the
center of the field of view. X-rays from the two internal
calibration
sources are also visible. The intensity scaling is logarithmic to enhance
low luminosity features.
Helping to Solve the Gamma-Ray Burst Mystery?
On July 20, a gamma-ray burst was simultaneously detected in the gamma-ray
burst monitor (GRBM, 60-600 keV) and one of the wide-field camera X-ray
detectors (WFC, 2-30 keV) aboard BeppoSAX. The WFC provided an image of the
field with a resolution of 5 arcminute (FWHM). The burst position is
R.A.= 17h29m36s, Decl.= +49 02'.2 (equinox 2000.0). It will be possible to
refine the position to a 1.5 arcminute error-box radius after additional
calibrations. This position lies within 0.25 degrees of the center of the
2-degree error box of a simultaneous
CGRO/BATSE event.
Once scientists knew exactly where to look, other instruments were pointed
at the BeppoSAX burst location. Observing from
radio to X-ray, no peculiar
sources have been found which can be definitively linked to the source of the
gamma-ray burst. So, while the gamma-ray burst mystery continues, SAX has
already proven itself to be a powerful new tool for scientists to use to probe
for an answer to just what generates these incredible bursts of energy.
"The more instruments we have, in as broad an energy range as we can get,
which can react quickly to look in a precise location in the sky, the better
our chances are of seeing something that will provide insight," said one
high-energy astronomer.
A Satellite Called Beppo?
Giuseppe "Beppo" Occhialini was born in 1907 in Fossombrone, Italy.
He graduated in Florence in 1929. At the age of 24, he joined the Cavendish
Laboratory in Cambridge, under the supervision of Patrick M.S. Blackett. He
brought the coincidence counter technique to the Laboratory, pioneered by
Bruno Rossi, and applied it to the Wilson chamber. The famous picture of the
first electromagnetic shower was obtained with this device, providing a firm
confirmation of the discovery of the
positron.
After the Second World War, he moved to the Will Laboratory and worked
with Cecil P.S. Powell in Bristol, UK. There, using a novel approach involving
the use of photographic emulsions for detection of elementary particles, he
contributed to the discovery of the pi-meson decay in 1947.
In 1952, Occhialini became professor of advanced physics in Milan.
He played a crucial role in starting the European Space Research
Organization, fore-runner of today's European Space Agency.
He was one of the founding fathers of the COS-B project.
Giuseppe Occhialini died on 30 December 1993. The SAX satellite was
named BeppoSAX in his honor in 1996.
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