21st Announcement of Opportunity (AO-21)


The AO21 review has been completed in November 2023, and the results can be found under:

This Announcement solicits proposals for observations to be carried out in 2024. The letter from ESA's Director of Science, inviting you to participate in the 21st Call for Proposals, is available here.


Release of AO-21: Call for observing time proposals   4 September 2023
Deadline for submission of observing time proposals   29 September 2023 (14:00 CEST)
Meeting of the Time Allocation Committee (TAC)   24-26 October 2023
Start AO-21 cycle of observation   1 January 2024

Special about AO21 as last call for INTEGRAL Observations

As the Science Programme Committee (SPC) has mandated ESA to close science operations of INTEGRAL as of 31 December 2024, AO21 is the final call, thus your last opportunity to use INTEGRAL for your science. This makes AO21 different from previous and we would like to give some advice how to make best use of this last chance:

  • Consider what are the most unique capabilities of INTEGRAL that will no longer be available once INTEGRAL is gone: highlight what cannot be done with other missions in the future and why the science must be done before INTEGRAL closes science operations.
  • TOO observations are opportunities for doing new science and will continue to be an important element of INTEGRAL's observing programme.
  • If there are any science ideas you have held back for some reason, this is the last chance to give it a try.
  • If you are new to INTEGRAL, we have prepared a Brochure summarizing in a nutshell INTEGRAL's science capabilities with some examples.
    If there are any doubts about feasibility of a new idea, don't hesitate to ask the INTEGRAL Helpdesk. While demonstrating feasibility is responsibility of the PI and there are supporting tools (see below), we are happy to help and discuss.
  • While the instruments are complex, powerful tools linking raw data with state of the art calibration makes it very easy to obtain calibrated data ready for scientific interpretation. So, even if you are not familiar with INTEGRAL data analysis, be assured: there are good tools and help is always near.

Important Notes

Please take note of the following points:

  • During their meeting on 7 March 2023, ESA's Science Programme Committee (SPC) confirmed the continued science operations of INTEGRAL until the end of 2024, enabling support of the fourth observing run of the gravitational wave detectors LIGO, Virgo, and KAGRA. This allowed us to have the current release of AO-21. We encourage the scientific community to submit proposals for INTEGRAL observations to be scheduled during 2024. Details of the mission can be found in the Overview, Policies, Procedures document. More information on the various instruments is given in the documents listed below.

  • ESA provides the opportunity to propose for INTEGRAL observations to be coordinated with XMM-Newton, NASA's NuSTAR telescope and/or NASA's Neil Gehrels Swift Observatory with a total of 300 ks, 100 ks and 150 ks, respectively, of their available time. Note that through an agreement with ESA, the Fermi project of NASA offers the possibility to obtain observing time with INTEGRAL through a single proposal to NASA via the Fermi AO.

  • Following a recommendation by the INTEGRAL Users Group (IUG), the time for execution of Targets of Opportunity (TOO) observations during AO-21 is limited to 3 Ms. This is allocated to allow for long-term planning before the start of the AO. More time may be allocated to TOO observations during the execution of the AO if justified on the basis of scientific merit. Note that if a TOO is warranted, which is not approved for the current ongoing AO, an out-of-TAC (or unsolicited) TOO may be requested. Examples are new events or unexpected behaviour in known sources. Requests are to be submitted via the INTEGRAL TOO Notification web page.

  • The INTEGRAL Project has signed a Memorandum of Understanding (MoU) with the IceCube Collaboration, and Letters of Intent (LoIs) with the deep-sea neutrino telescope ANTARES and the SUPERB Project to participate in follow-up campaigns of ultra high energy neutrino events, and fast radio bursts. It is important to note that it is not possible to propose for time bound by these MoUs/LoIs.

  • In this AO it is not possible to submit new Key Programme proposals with observations spanning two AO cycles (so-called multi-year proposal).

  • The rectangular dithering on a 5x5 grid is the standard observation pattern. In a few cases a hexagonal pattern is allowed. Observations with custom patterns are strongly discouraged. They will be considered only for A-grade proposals, and their scheduling will be on best-effort basis.

  • Data or science rights to the targets or science in the field of view (FOV) of the instruments will be allocated to PIs of accepted proposals with a 1-year proprietary period. If the PI is from a country other than the Russian Federation, the rest of the field will be made public immediately. Proposals where the PI is from the Russian Federation follow a similar kind of policy, except that the rest of the field will be made public only through the consolidated data programme. The Russian Federation scientists currently working at Russian Federation scientific institutes still have exceptional access to the near-real time data of the rest of the field.

  • Due to star-tracker viewing constraints, INTEGRAL cannot point to the Earth and/or other Solar system objects (including our Moon). There is, however, a way to circumvent this: let the object pass through the field-of-view of the instruments. Such observations have been done in the past, but they require special operations. Anyone interested in studying Solar system objects, is encouraged to contact us via the INTEGRAL Helpdesk.

For the Scientific Justification of your proposal, you are encouraged to use this LaTeX template, and refer to this checklist.




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