Review applauds XMM-Newton’s greatly increased efficiency
After the recommendations of a first review last July of XMM-Newton
science operations, ESA’s Director of Science has congratulated all those
involved for greatly improving the mission’s efficiency, particularly the
management of the X-ray observatory’s observations.
Professor Roger Bonnet was speaking at a ‘Delta Review’ held 13 February
at the XMM-Newton Science Operations Centre at VILSPA. The mission’s
management presented the latest statistics on the observation programme
efficiency, the instrument performance and the data distribution. Also
present at the meeting were the XMM-Newton Principal Investigators, the
Head of ESA’s Astrophysics Department Brian Taylor, and David Southwood,
the Agency’s next Director of Science.
“Compared to the 35% level only six months ago, the efficiency of our
science observations has dramatically increased,” Science Operations
Manager Jean Clavel told them. “Over ten complete revolutions in January
we reached 61%. This is comparable to the Chandra mission. Our most
recent figures do show a slight drop to 55%, the consequence of both our
Perth and Kourou tracking stations being mobilised for the launch of an
Italian satellite. But we now have routine hands-on experience and are
very confident that we can reach a 70% efficiency.”
This further improvement will stem from the Santiago tracking station
which has just been brought online. Covering the apogee gap, it will
allow greater scheduling flexibility and longer observations, getting
the maximum from each 48-hour orbit.
Spacecraft operations are nominal, there have been no problems during
eclipse periods and the satellite has comfortable — solar array
generated — power energy margins for the remainder of the mission. The
ground segment is now receiving 99% of all the available science data
telemetry.
The X-ray imagers and X-ray spectrographs are continuing to perform
remarkably well. Error margins (for instance with the X-ray photon
count) have fallen from 30% in June last year to 10% at present.
Cross-calibration — which allows observations to fully exploit the
complementary aspects of all the instruments — has also improved to
practically 5%, with an ultimate target of 2%.
The observatory has also already carried out a considerable number of
coordinated observations with other spacecraft (Chandra, BeppoSAX, and
RXTE) or with ground-based telescopes (VLA, VLBI, Cangaroo).
Astronomers have understandably been impatient to quickly receive their
observation data, and the review dwelt at length on the issue of data
distribution. “Because software was not completely ready we did not want
to ship raw data telemetry without also providing processed data which
immediately makes sense for scientists,” explains Jean Clavel. “Now we
have cleared this hurdle and the Science Survey Consortium is routinely
processing all the data. The first 21 sets of Observation Data Files
(ODF) and associated ‘pipe-line’ products were shipped on 15 February.
Henceforth we will be producing the required CDs within one month, at
the most, of an observation.”
A final question to be considered was the balance between open- and
guaranteed-time observations. Because of the initial lower than expected
efficiency, and a number of left over calibration and performance
verification observations, the period during which XMM-Newton would
exclusively observe guaranteed time has had to be extended. With some
slight modifications to the remainder of the guaranteed/open time
subdivision, it is now possible to perform an adequate amount of
guaranteed time observations, while still finishing AO-1 almost on
schedule.
“I am confident that with the time distribution profile that has now
been agreed for the remainder of the mission we will have the right mix
of guaranteed and open-time observations,” says Project Scientist Fred
Jansen. “The important factor being the availability of open-time data
to the AO-1 proposers.”
“I can say that we are all really pleased to see such an improvement in
the mission’s efficiency and that we no longer have any problems today”
said Roger Bonnet. But he insisted that “fully opening the tap” on data
distribution was still a major concern. “We must make sure that the
extraordinary effort over the past few months is prolonged by getting
the data out quickly. But I am extremely satisfied and I am sure that
we are going to ensure the observatory’s smooth operations for the next
decade.”
USEFUL LINKS FOR THIS STORY
* XMM-Newton home page
http://sci.esa.int/home/xmm-newton/
* XMM-Newton mosaics the Coma cluster of galaxies
http://sci.esa.int/content/news/index.cfm?aid=23&cid=750&oid=24817
* Santiago comes online
http://sci.esa.int/content/news/index.cfm?aid=23&cid=45&oid=26113
* XMM-Newton Science Operations Centre home page
IMAGE CAPTIONS:
[Image 1:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=23&cid=12&oid=26203&ooid=26204]
Delta Review with (left to right front row) Brian Taylor, David Southwood
and Roger-Maurice Bonnet.
[Image 2:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=23&cid=12&oid=26203&ooid=26205]
XMM-Newton efficiency at the time of the June 2000 review (left), and at
the time of the February 2001 review.
[Image 3:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=23&cid=12&oid=26203&ooid=26206]
XMM-Newton has again observed the Coma Cluster of galaxies, with far
longer exposures. Certain regions were observed for 22.6 Ksecs instead
of 3.4 Ksecs originally, and with a lower proton background. Shown at
the Delta Review, the new EPIC-pn image covers the 0.3 to 2.0 keV energy
range and clearly discerns far more sources. The difference is striking
particularly in the north/west (upper-right) corner. Courtesy U.Briel.
[Image 4:
http://sci.esa.int/content/searchimage/searchresult.cfm?aid=23&cid=12&oid=26203&ooid=26207]
New XMM-Newton EPIC-pn image of the Coma Cluster. With more processing,
comparison of the low energy 0.3-2 keV band (left) with the 2-5 keV high
energy band (right) highlights a “hot bubble”, almost exactly between the
main cluster and the galaxy group around NGC4839. Courtesy U.Briel.
