At the end of January and the beginning of February 2006
INTEGRAL observed the Earth. The goal of the observation was to measure the
cosmic high energy background by using the Earth as a blocking device
and measuring the change in flux while part of the field of view was
covered by it.
This is by no means a standard observation and therefore a lot of
special operations were needed for the planning of these observations
from ISOC, MOC and the instrument teams.
Since it is impossible to steer the satellite while the illuminated
part of the Earth blinds the star trackers, INTEGRAL was pointed at a
stationary position in the sky and the Earth drifted through the field
of view of the instruments.
The picture shows at the top the image as obtained with the SPI
instrument (2.5 deg angular resolution) between 25 and 50 keV. The
earth stands out as a dark "hole" in the middle of the image.
At the bottom left a light curve obtained with the JEM-X instrument in
the energy range 3-5 keV for one of the observations is displayed
together with various model contributions (sky background,
instrumental background and a small contribution from the Earth's
aurora) which altogether describe the observed light curve quite well.
At the bottom right a similar light curve obtained with the ISGRI
instrument in the range 20-40 keV is shown, presenting a similar but
not identical profile as at lower energies.
Work is ongoing to analyze this unusual observation.
Credits: A. Neronov (ISDC, Geneva); E. Churazov (IKI, Moscow);
J.-P. Roques (SPI team); F. Lebrun, P. Ubertini (IBIS team);
N. Lund (JEM-X team)
