Given the exceptionally enthusiastic response to the European Space Agency's first call for guest observers to use its INTEGRAL gamma ray observatory, the committee assigned to judge the applications faced a daunting task
When the mission's Time Allocation Committee (TAC) gathered May 14 for a weeklong meeting in Noordwijk, the Netherlands, they found 291 submissions waiting -- 19 times the number of slots allocated for guest observers in the observatory's first year of operation.
"It was an enormous challenge, not just with the oversubscription but also because of the overall high quality of the proposals," said Edward van den Heuvel, TAC chair and director of the Astronomical Institute at the University of Amsterdam.
The 28 TAC members from 10 different ESA member states, Russia and the United States spent the first four days of the meeting locked in lengthy panel meetings devoted to four broad domains of gamma ray astronomy:
- compact objects
-- such as black hole candidates, neutron stars and pulsars;- extragalactic objects --
principally active galactic nuclei, different kinds of galaxies and clusters of galaxies;- nucleosynthesis --
including supernova remnants, diffuse emission and interstellar phenomena;- miscellaneous topics
-- including gamma ray bursts (GRBs).
In each category committee members considered the submissions in light of essential issues such as scientific importance and originality; soundness of scientific argument; understanding of INTEGRAL's instruments; the target's gamma ray intensity (and consequent likelihood of a successful observation) and whether INTEGRAL access was necessary to the observation as proposed.
After two referees offered initial comments, the panel members -- like teachers facing stacks of examination papers -- redlined and dissected each proposal while representatives of the INTEGRAL Science Operations Center gave their view on the submissions' technical feasibility.
Intense debate
Intense lively debates often broke out for and against the proposals, sometimes sidetracking panel members into expounding their personal scientific views about the target. At these times, the panel chairmen, constantly watching the clock to keep to the schedule, had to harness the overflow of enthusiasm.
It was a marathon exercise.
"Most of the panels averaged 10 to 15 hours of work each day and, as the end drew near, we were burning the midnight oil to get through the remaining proposals," said one committee member.
Out of concern for absolute fairness, panel members associated with proposals under consideration were asked to excuse themselves.
On the final day, the four panel chairmen summed up their recommendations in a meeting with Professor van den Heuvel and INTEGRAL project scientist Chris Winkler. All observation proposals were ranked in order of priority:
A: excellent, must be executed;
B: good, should be executed;
C: doable, not rejected.
Those that did not fit into the above grades were rejected.
Looking for about 25 finalists
"We set out to go down from the factor-19 oversubscription to something like two or three which we have to retain as a margin for scheduling reasons," Winkler explained.
"The TAC has examined everything but we are far from having finished," he said. "It is clear, and a great pity, that some accepted proposals may not be done during AO-1 [the first year of observations], but we still have to see how much we can amalgamate, or if we can combine different proposals which share targets in their fields of view. Furthermore, A- and B-grade proposals can be transferred to AO-2 if they can't be scheduled in AO-1."
Professor van den Heuvel commented on another important aspect of the selection process.
"We also have to achieve a balance between the different scientific interests, such as between nucleosynthesis and the study of compact objects, and between long and short observations," he said. "A lot of bargaining lies ahead."
The TAC will meet again in a few weeks to draw up a first draft of the guest-observation program. Further amalgamations and consolidations will follow before final recommendations are submitted to ESA's director of science.
The definitive list of approved observations is scheduled to be announced this summer.
advertisement
advertisement
