Astron. Astrophys. Suppl. Ser. 133, 431-436

Spatial corrections of ROSAT HRI observations

D.E. Harris¹ - J.D. Silverman¹ - G. Hasinger² - I. Lehmann²

Send offprint request: D.E. Harris; harris@cfa.harvard.edu

1 - Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, U.S.A.
2 - Astrophysikalisches Institut Potsdam, An der Sternwarte 16, D-14482 Potsdam, Germany

Received June 29; accepted July 7, 1998

Abstract:

X-ray observations with the ROSAT High Resolution Imager (HRI) often have spatial smearing on the order of 10$\hbox{$^{\prime\prime}$}$ (Morse 1994). This degradation of the intrinsic resolution of the instrument (5$\hbox{$^{\prime\prime}$}$)can be attributed to errors in the aspect solution associated with the wobble of the space craft or with the reacquisition of the guide stars. We have developed a set of IRAF/PROS and MIDAS/EXSAS routines to minimize these effects. Our procedure attempts to isolate aspect errors that are repeated through each cycle of the wobble. The method assigns a "wobble phase" to each event based on the 402 second period of the ROSAT wobble. The observation is grouped into a number of phase bins and a centroid is calculated for each sub-image. The corrected HRI event list is reconstructed by adding the sub-images which have been shifted to a common source position. This method has shown $\sim$$30\%$ reduction of the full width half maximum (FWHM) of an X-ray observation of the radio galaxy 3C 120. Additional examples are presented.

Key words: techniques: image processing -- X-rays: general