ROSAT Guest Observer Facility

What are the "ghost images" I've heard about?


The "ghost images" occur because the electronic pulse for low-energy events is sometimes too small to exceed the lower-level discriminator threshold, so an incorrect position of the photon is assigned. Position information comes from the crossed cathode wires (energy information comes from the anode wires), with an interpolation done for the nearest wires. At low pulse height, only one voltage reading is available, hence the incorrect position. The PSF becomes non-uniform, and non-monotonic at the lowest pulse heights. Images containing electronic ghosts will have a boxy appearance, with the real source surrounded by a box of satellite sources, one satellite at each remaining position of a 3x3 square. The image size, including satellites, is about 5' on a side. If a circle of radius 2'.25 is centered on the source, about 50 percent of the flux lies outside it for channels 1 and 2 (34-channel matrix), about 15 percent lies outside for channels 3 and 4, and about 0 percent lies outside the circle beyond channel 5.

button Select another question related to this topic

Select another FAQ topic Select another FAQ topic Return to the ROSAT GOF Return to the ROSAT GOF

Please use the Feedback link if you have questions on ROSAT.

This file was last modified on Friday, 27-Jul-2001 14:59:28 EDT

NASA Astrophysics

  • FAQ/Comments/Feedback
  • Education Resources
  • Download Adobe Acrobat
  • A service of the Astrophysics Science Division (ASD) at NASA/ GSFC

    ROSAT Project Scientist: Dr. Robert Petre

    Responsible NASA Official: Phil Newman

    Privacy Policy and Important Notices.