IXPE Target of Opportunity (ToO)

IXPE ToO observation requests will not be considered for events or sources that could have been predicted or proposed for in advance. If the ToO is accepted, it will take 3 calendar days or so from the time you submit this form until IXPE can slew to the target and start observing.

IXPE should not be used just to measure the X-ray flux of a source. IXPE is intended to measure the polarization of X rays, which requires a large number of counts. It will help your proposal if you can estimate the level of polarization you expect to see from your source. In any case, you must estimate the Minimum Detectable Polarization (MDP) you expect to achieve with this observation. Both the source count rate and MDP can be estimated using WebPIMMS .

The ability to get data off the spacecraft is limited and this limits how long a bright source can be observed before we need to switch to a faint target. For example, the Crab can only be observed for 2 days before the on-board storage is filled (assuming it was empty at the start) and it will take up to a week to download the data. Therefore, proposers also need to estimate the source counting rate in the full IXPE band using WebPIMMS .

Please review the IXPE Long Term Plan to see if your proposed target is not already listed.

Please check to see if your target is currently observable with IXPE using viewing.

IXPE data associated with ToO requests will have no exclusive use period and will be available via the public archive at the HEASARC nominally within one week of completion of the observation.

In the first two years, we encourage the community to collaborate with the IXPE science team. If the mission is extended a full GO program will be implemented.

Principal requester
Primary Email address
  (additional email addresses can be supplied in Remarks section below). Note, if you do not get an email sent to this address, the ToO form also was not sent to the IXPE team.
Best way to reach me (email, phone)
24 hr Contact info
Scientific Justification
Object type
Scientific Justification
Clearly and concisely explain the need and scientific potential for this ToO.
Relevant URLs
This is for supplementary information and not a substitute for the above Scientific Justification.
Justification for this particular target
Likelihood of detection, duration,
and recurrence of transient behavior
Response time requested Examples: <72 hours or within 2 weeks

Justification for requested response time
Target details
Target Name
RA (J2000 decimal degrees from 0.0 to 360.0)
Dec (J2000 decimal degrees from -90.0 to 90.0)
Observing time (kiloseconds)
Justification for observing time
Give details of any source modeling. Please state assumptions about energy bands, phase bins etc. used to estimate MDP.
Approximate expected spectrum
Expected count rate in the full IXPE (PIMMS default) band
If expected count rate is too high, an attenuating filter may be used.

Expected MDP99
If you plan coordinated observations, please identify other observatories and associated time constraints.
Additional Comments
Enter any other questions/remarks/comments

Clicking the Submit button sends emails to the IXPE operations team. A confirmation email will be sent to the 'Primary Email address' field at the time of submission. After review by the IXPE PI and the operations team, you will be contacted with a decision to approve or decline the request.
Last updated: Thursday, 11-Aug-2022 13:16:09 CDT