The Multi-Instrument Ramp Generator, or Mirage, has been released for public use. This Python software package creates simulated data for a significant subset of the science observing modes of NIRCam and NIRISS, including Imaging and Wide Field Slitless Spectroscopy (WFSS) data for both NIRCam and NIRISS. Mirage also supports imaging with the JWST Fine Guidance Sensor (FGS) used for engineering testing purposes.

The Mirage development was led by the STScI NIRCam and NIRISS instrument teams to produce semi-realistic simulated JWST test data. While the primary use case is to inform the development of the calibration pipeline, data analysis tools, and to help plan commissioning activities, Mirage can now also be used by JWST observers.

Simulated data from Mirage and MIRISIM can provide JWST observers with a deeper understanding of the quality and layout of JWST data. They can also help observers develop their own data processing workflows and practice analyzing JWST data before launch.

Key features of Mirage include:

• Mirage is semi-empirical: Data cubes are simulated by adding astronomical sources to real dark current data from ground testing. The resulting simulations contain some of the same instrumental noise sources and effects that will be present in in-flight data.
• Mirage can produce complex astronomical scenes: Point sources are calculated using pre-computed WebbPSF filter- and position-dependent PSFs. Users may create scenes consisting of point sources, Sersic-profile galaxies and arbitrary fits images representing sources with more complex morphologies.
• Mirage supports non-sidereal targets: There are two non-siderial modes. The first mode models non-siderial objects crossing the field of view within an exposure. The second mode models a non-sidereal tracking observation where sidereal objects drift across the field of view.
• Mirage can create simulations from APT files: By ingesting an APT file, Mirage can automatically create a set of simulated exposures, as described by a JWST proposal.
• Mirage outputs approximate the format and header information of in-flight data. Outputs from Mirage can be ingested by the JWST calibration pipeline, mimicking the data reduction strategy to be used for in-flight data.

The Mirage code base is available on github. User documentation and installation instructions are is available on readthedocs.