Telescope

Observing modes

Diverse strategy, dynamic science. Because every unit carries its own filters, the array can be reconfigured for spectral resolution, depth or coverage without touching the hardware.

Principle

One array, four configurations

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 unique filter combinations to individual units and rotating through them during an observation. Four modes are in routine use, and the choice between them is the choice of what to spend the night on: spectral resolution, depth, or sky coverage.

  • 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 that makes 7DT behave like a low-resolution spectrograph 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 whether a source is there at all.

  • 03

    ColorBroadband, fast

    Broad-band filters only. Chosen for faint, fast events such as gamma-ray bursts and young supernovae, where detection early on the light curve matters more than spectral detail.

  • 04

    SearchMaximum sky coverage

    Each unit points at a different region of sky. The optical counterpart of a gravitational-wave event is reported as a probable region over a wide area, and tiling it quickly is worth more than observing any one field well.

Schematic

Filter assignment across the array

Schematic of 7DT observing modes and filter assignment
Modes The full spectral range is covered by giving each unit a unique filter combination and rotating through it during a target observation.
Response

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 ToO observation finishes the array returns to the queue, resuming the interrupted target if it is still observable. Response time from alert ingestion to the start of a follow-up exposure is under one minute.

How ToO data are processedSurvey design