ESA INTEGRAL Status Report – February 2004
Mission Status
INTEGRAL routine operations continue to run smoothly except for an
interruption due to high solar activity between 2003 October 26 to November
7, during which time the instruments were switched-off. This interval
included an X28 solar flare . one of the brightest seen this century. Other
than an occasional loss of a guide star due to the enhanced background and
an increased amount of solar panel degradation (equivalent to about 4 months
of normal operations), INTEGRAL survived the enhanced solar activity safely.
The Time Allocation Committee (TAC) for the second INTEGRAL Announcement of
Opportunity met in October and selected the observations to be performed
from 2003 December 17 onwards. This was no easy task given the high (factor
~8 in time) over-subscription. All the AO-2 proposers have been notified of
the TAC decisions and a long-term plan until February 2005 is available
under http://astro.estec.esa.nl/Integral.
Operations and Archiving
Besides the interruption due to the enhanced level of solar activity, the
observing programme continued with a good efficiency with over 93% of the
available observing time (when Integral is above the radiation belts) being
used for scientific observations. The ground segment is operating well with
the detailed INTEGRAL schedule being typically available between two weeks
and one month in advance allowing other facilities to coordinate with
INTEGRAL, if desired.
In order to mitigate the effect of radiation damage on the SPI detectors, it
is necessary to periodically anneal or .bake. them. The first such annealing
cycle was successfully performed in 2003 February and the second in 2003
July. However, the second annealing did not fully recover the energy
resolution of the detectors indicating that the baking out period was too
short. An additional, longer duration, annealing was performed in November,
after the solar activity had subsided. An analysis of SPI spectra showed
that the annealing was fully successful with the energy resolution being
fully recovered to its pre-launch values.
On 2003 December 6 one of the 19 SPI detectors suddenly stopped operating.
Various recovery attempts have been unsuccessful. Analysis indicates that
fault is most likely a component failure in the detector.s pre-amplifier.
The SPI team, together with ex-INTEGRAL project team members and SCI-A
personnel are continuing to investigate the failure and may propose
additional recovery actions. A preliminary analysis of the reduction in SPI
scientific performance indicates that this is limited to the ~5% reduction
in effective area.
After the closure of the autumn galactic centre visibility window, INTEGRAL
continued making scans of the central radian of the galaxy and along the
galactic plane searching for new transients and other interesting phenomena.
In addition, the accreting low-mass X-ray binaries XB 1916-053 and 4U
0614+09 were observed together with the galactic micro-quasar GRS 1915+105.
Taking advantage of the large INTEGRAL field of view, the blazar 0716+714
has been observed simultaneously with the Seyfert galaxies Mkn 3 and Mkn 6
which lie in the same region of sky. The observation of the active galactic
nucleus MR 2251-178, which was started in 2002 December, was completed. Deep
(1 to 2 x 106 sec) observations of the Vela region, and the Cas A (together
with Tycho) and IC 433 supernova remnants have been performed, primarily to
study nucleosynthesis by characterizing the gamma-ray line emission.
The third release of the Integral Science Data Centre (ISDC) public off-line
scientific analysis (OSA) software occurred in 2003 December. The new
release includes increased functionality, particularly for the low-energy
imager (ISGRI) where the uncertainties associated with image reconstruction
have been sharply reduced and spectral extraction algorithms improved. For
the X-ray monitor (JEM-X) improved background models and data extraction
algorithms are included. The ISDC continues to routinely dispatch data
products to observers within 6 weeks of their observation. Using results
obtained with OSA-3, the ISDC and instrument teams are evaluating the
in-flight instrument sensitivities in order to verify or update those
published in the AO-2 documentation.
Science Highlights
A special edition of Astronomy & Astrophysics dedicated to INTEGRAL (volume
411, 2003 November) has appeared containing 73 papers covering mission and
instrument descriptions and performance and early science results.
A paper based on INTEGRAL results has been submitted to Nature (Lebrun et
al.). This addresses the nature of the 20 to 200 keV Galactic gamma-ray
emission. Below and above this energy range diffuse emission processes
dominate, but the nature of the emission in this energy range was, until
now, highly uncertain. Deep ISGRI observations of the central portion of the
Galaxy have revealed 43 point-like sources. The integrated flux from these
faint sources fully accounts for the shape and intensity of the 20 to 200
keV spectrum observed by previous missions. This means that the soft
gamma-ray spectrum of the Galaxy is dominated by emission from compact
objects, such as black holes and neutron stars in binary systems.
After observing one gamma-ray burst a month in the INTEGRAL field of view
for the first 6 months of the mission, astronomers had to wait another 6
months to observe the seventh! This (GRB 031203) was detected and positioned
automatically by the burst alert software (IBAS) running at the ISDC and an
alert sent out within 20 sec of the burst occurring with an uncertainty
radius of only 2.7 arc minutes. This allowed XMM-Newton to observe the field
within 6 hours of the burst . currently their fastest Target of Opportunity
response to date. A fading X-ray afterglow was detected surrounded by an
expanding ring of emission. While predicted, such an expanding ring has
never been seen before and is most likely due to X-rays scattered off dust
grains in our own Galaxy.
