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ACIS ○̉｜Definition｜1st｜20251119205401-00-⌔

Advanced CCD Imaging Spectrometer - Wikipedia

Advanced CCD Imaging Spectrometer

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The Advanced CCD Imaging Spectrometer (ACIS), formerly the AXAF CCD Imaging Spectrometer, is an instrument built by a team from the Massachusetts Institute of Technology’s Center for Space Research and the Pennsylvania State University for the Chandra X-ray Observatory.

ACIS is a focal plane instrument that uses an array of charge-coupled devices. It serves as an X-ray integral field spectrograph for Chandra. The instrument is capable of measuring both the position and energy of incoming X-rays.1

The CCD sensors of ACIS operate at −120 °C (−184 °F) and its filters at −60 and −50 °C (−76 and −58 °F). It carries a special heater that allows contamination from Chandra to be baked off; the spacecraft contains lubricants, and the ACIS design took this into account in order to clean its sensors. Contamination buildup can reduce the instrument’s sensitivity.2 Radiation in space is another potential danger to the sensor.3

As of 2014, after 15 years of operation, there was no indication of a limit to the lifetime of ACIS. Another design feature of the instrument was a calibration source that can be used to understand its health. This allows for a measurement of the level of contamination, if present, as well as any degree of charge transfer inefficiency.3

Printed 2026-06-28.

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Footnotes

  1. “Science Instruments”. Chandra X-ray Observatory. NASA/Smithsonian Astrophysical Observatory. 19 September 2013. Retrieved 20 January 2017. ↩

  2. Roy, Steve; Watzke, Megan (13 November 2003). “Chandra Advanced CCD Imaging Spectrometer (ACIS) update”. NASA. Retrieved 20 January 2017. ↩

  3. Grant, Catherine E.; Bautz, Mark W.; Ford, Peter G.; Plucinsky, P. P. (24 July 2014). “Fifteen years of the Advanced CCD Imaging Spectrometer”. In Takahashi, Tadayuki; Den Herder, Jan-Willem A.; Bautz, Mark (eds.). Space Telescopes and Instrumentation 2014: Ultraviolet to Gamma Ray. Proceedings of the SPIE. Vol. 9144. SPIE. 91443Q. arXiv:1407.6677. Bibcode:2014SPIE.9144E..3QG. doi:10.1117/12.2055652. S2CID 119124482. ↩ ↩2

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ACIS ○̉｜Definition｜1st｜20260113010816-00-◊

ACIS Information Page

ACIS Instrument Information

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Recent memos: Update on ACIS contaminant, Jan 8 2010

The Advanced CCD Imaging Spectrometer (ACIS) is an X-ray imager. X-ray photons hitting the camera are detected individually and their position, energy and arrival time recorded. This allows for high resolution (~1 arcsec) imaging, moderate resolution spectroscopy and timing studies. ACIS can also be used with the High Energy Transmission Grating (and less commonly the Low Energy Transmission Grating) for high resolution spectroscopy.

The Instrument layout is shown to the right. The back illuminated S3 chip offers the best spectral resolution without using a grating. For this reason, many observers choose the back illuminated S3 chip for high resolution imaging over small (few arcminutes) fields. The largest field of view is obtained by turning on the 4 ACIS-I front illuminated chips. This configuration is often used for surveys. The table below summarizes common instrument configurations, although others are available.

A complete description of ACIS is given in the ** Proposers’ Observatory Guide**.

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