How to propose
What the array can be asked to do, how an observation is specified, and how time is requested.
Four observing modes
Because each unit carries its own filter complement, the array can be reconfigured between science goals without changing hardware. The full spectral range is covered by assigning different filter combinations to individual units and rotating through them during an observation. Four modes are in routine use; the choice between them trades spectral sampling, depth and sky coverage against one another.
- 01
SpecMaximum spectral resolution
The default mode. Units rotate through every available medium and broad band, covering the full spectral range in as few exposures as the filter distribution allows. This is the mode in which 7DT delivers low-resolution spectroscopy over 1.25 square degrees.
- 02
DeepMaximum depth
A selected subset of filters is used, trading spectral sampling for signal-to-noise. Used when the question is detection rather than characterization.
- 03
ColorBroadband, fast
Broad-band filters only. Used for faint, fast events such as gamma-ray bursts and young supernovae, where early detection on the light curve matters more than spectral detail.
- 04
SearchMaximum sky coverage
Each unit points at a different region of sky. A gravitational-wave counterpart is localized only to a probable region covering a wide area, so covering that area quickly takes priority over observing any single field deeply.
What an observation request contains
An observation is specified by target position, observing mode, exposure time and the number of repetitions, together with any constraint on airmass, moon separation or time window. Positions on the survey tiling are preferred where the science allows, because data taken on a tile coadd directly with existing survey data and can be differenced against the reference image without an additional calibration step.
Before requesting time, check the target is observable from El Sauce in the intended window, and check what already exists: much of the southern sky already has a medium-band reference image, and the tile under a given position may already carry the bands needed.
Check visibility and existing coverage — the data access page reports the bands and frame counts held for any position.
Estimate depth from the measured limiting magnitudes rather than from the aperture.
Target visibility and filter response can be computed with
supy.
Target of opportunity
When a transient alert arrives — a gamma-ray burst, a gravitational-wave candidate — the scheduler interrupts the observing plan and repoints. Two response modes are available: a regular mode that completes the current exposure block before switching, and a rapid mode that interrupts immediately. Once the follow-up finishes, the array returns to the queue and resumes the interrupted target if it is still observable. Time from alert ingestion to the start of a follow-up exposure is under one minute.
Target-of-opportunity data are processed at elevated priority and the requester is notified when raw data arrive, as each filter set completes, and on completion with a spectral energy distribution plot and magnitude table attached.
178 follow-up campaigns have been carried out since automated target-of-opportunity response entered service, 9 of them on gravitational-wave events.
LVK superevent identifiers as issued in the public alert stream. Target-level details are not published here.
Requesting observing time
Observing time is currently allocated within the collaboration and its partner institutions; there is no general call for proposals yet. A proposal template and an exposure time calculator will be published on this page when one opens. Enquiries about observations outside the survey program, including target-of-opportunity requests, should be addressed to the project directly.
Contact the project