NuSTAR Target of Opportunity (ToO) or Directors Discretionary Time (DDT) observation request

NuSTAR observatory operations will continue during the COVID-19 pandemic including all approved ToO programs.

NuSTAR ToO and DDT observation requests will in general not be considered for events or sources that could have been predicted and proposed for in General Observer (GO) programs. This restriction is being adopted as a result of guidance from NASA's 2019 Senior Review.

In particular, requests for observations of the following types of sources and events require special justification describing why the requested observation type could not have been proposed as a GO target:

  • Known or candidate black hole systems
  • Known or candidate pulsar or magnetar systems
  • Candidate counterparts of gravitational wave or astrophysical neutrino detections
  • Nova or Supernova events
  • Luminosity variations from known or candidate AGN (including blazars and Tidal Disruption Events)
  • Observations of the Sun or other Solar system objects
  • Observations of events with specific time constraints
  • Observations coordinated with other observatories that could have been proposed for to joint GO programs
As a specific example, binary systems where periastron intervals are known can be proposed to the GO program, with observations triggered from monitoring of activity by other observatories. Observations that are simultaneous with ground or space based activities can also be proposed to the GO program, even if the exact dates for the coordinated observations are not known at the time of the proposal.

We encourage the community to propose to the various peer reviewed GO programs for NuSTAR ToO observations. Observations of all selected GO ToO observations automatically have the highest priority for scheduling.

Active ToO/DDT observations
MAXI J0903-53120 ks     J2000 136.27866 -53.50518 PI Thalhammer
GX 339-42x25 ksPI Garcia
MAXI J0637-43010x50 ks for NuSTAR GO cycle-5 program 05213PI Tomsick
Last updated: 2021-04-22 1510 UT

Please review the NuSTAR schedules for details of upcoming observations and the table of approved ToO programs from the NuSTAR GO program and joint GO programs with Chandra, XMM-Newton, INTEGRAL, and the Neil Gehrels Swift Observatory.

Principal requester
Primary Email address:
      (additional email address can be supplied in Remarks section below)
Best way to reach me:
24 hr Contact info:
Scientific Justification
Object type:
Triggering an approved GO program: If yes, then give mission and GO proposal number:
Scientific Justification:
Relevant URLs
Justification for this particular target:
Likelihood of detection, duration,
and recurrence of transient behavior:
Response time requested: Examples: < 24 hours , < 48 hours , within 1 week , at directors discretion (DDT)

Note that the majority of approved ToOs have response times within 1 week
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)
from until
Date/time format options are described here. Default is UTC, unless you specify another time zone.
Observing time (kiloseconds)
Justification for observing time
(Give details of any source modeling, particularly for exposure time requests above 50 ks)
Expected NuSTAR count rate
(predicted instrument count rate for both modules using 50% PSF extraction with no dead time)

HEASARC WebPIMMS (set "Into:" field to 'NUSTAR') here.
Maximum expected NuSTAR count rate
(in case of flaring, bursts, etc)
Approximate expected spectrum
Source morphology
Coordination with other observatories?:

Clicking the Submit button sends emails and text messages to the NuSTAR operations team. A confirmation email will be sent to the 'Email:' field at the time of submission.

The request will be reviewed by the NuSTAR PI and the operations team and you will be contacted with a decision to approve or decline the request.

NuSTAR data associated with ToO or DDT requests submitted outside of approved GO programs will have no exclusive use period and, when completed, will be available via the public NuSTAR archive. See for more information.

A minimal set of data products for ToO/DDT observations performed within the last 14 days is also available as each observation progresses via the NuSTAR quicklook products webpage. Please carefully read the caveats on the use of this data detailed on the quicklook webpage.

Please contact   nustar-help at   if you have any questions.