In-Orbit vignetting calibration of the XMM-Newton telescopes

1. In-Orbit vignetting calibration of the XMM-Newton telescopes Marcus G. F. Kirsch, D.H. Lumb, A. Finoguenov, R. Saxton, B. Aschenbach, P. Gondoin, I. Stewart

2. XMM-Newton Mirrors • 3 Wolter Telescopes, with 58 concentric mirror shells each • focal length: 7.5 m • angular resolution: 6 arcseconds (FWHM ) • point-spread function: 15 arcsec (HEW)

3. VIGNETTING • VIGNETTING – the reduction in effective area with off-axis angle • important for: • cluster surface brightness • counts:flux conversions in population study • background normalisation • on-ground the X-ray measurements in Panter were in diverging beam and/or the grating stacks and stray light baffle were installed • in parallel UV beam no measurement of energy dependence • need to confirm the alignments survived thermal relaxation of optical bench, launch, and AIV campaigns • measure energy dependence in orbit D. Lumb

4. typical Vignetting result • compare vignetting with data in telescope calibration files • unexpected variations (~10%) in rel. vignetting with azimuth in PN • attributed initially to problems in BG correction and/or exposure time correction • but relative variations are correlated with camera orientation • possible misalignment of the telescope axis compared with nominal reference pn, 11 arcmin from nominal boresight

5. modifying telescope axis • on –ground data had been inconsistent to ~30 arcsec typically • mirror alignment cube either blocked or possibly moved during AIV ? • for each telescope could minimise discrepancies in measured vignetting by positing a telescope axis shift of up to 1 arcmin try to find sensitive method to determine the shift

6. the 4 methods • source at different position • diffuse background • source elongation • coma cluster 1 2 3 4

7. 3C58 and G21.5-0.9 D. Lumb M. Kirsch

8. vignetting: the shift MOS2 G21.5-09(stars) & 3C58 (squares) pn center at DETX=340 DETY=1300 D.H. Lumb

9. diffuse background • high galactic latitude background data sets compiled for cluster studies • removal of most sources, and co-addition of different fields leaves a very uniform surface brightness which should track the vignetting • modified by the particle background – has different vignetting function (cosmic rays flat, soft protons scatter down mirror system) D.H. Lumb

10. source elongation • With increasing off-axis angles sources become elongated (in direction tangential to their radius vector) • Plot elongation vs. angle to define centroid via mirror geometric properties R. Saxton

11. Coma cluster • a repeat observation of the cluster centre was made at new position angle • comparing surface brightness in same sky region reveals under- or over-correction (dotted line) • adjust the centroid of vignetting function to minimise these differences (solid line) A. Finoguenov

12. position of optical axis detector co-ordinates (0.05 arcsec)

13. position of optical axis currently under testing in DT SAS

14. calculate new BS angles • the new optical axis position required a set of new Boresight CCFs which hold for each instrument a triple of three angles describing the misalignment of the respective instrument boresight with respect to the satellite coordinate frame • using the OMC2/3 field new BS misalignment angles for all the three cameras have been calculated • goal: astrometry should not change!!!!!!!!!

15. astrometry: EPIC-2MASS old optical axis and BS: RA offset: -0.47 arcsec DEC offset: -0.55 arcsec RA offset: -0.15 arcsec DEC offset: -0.15 arcsec RA offset: -0.67 arcsec DEC offset: -0.81 arcsec new optical axis and BS RA offset: -0.95 arcsec DEC offset: -0.58 arcsec RA offset: -0.45 arcsec DEC offset: -0.15 arcsec RA offset: -0.78 arcsec DEC offset: -0.40 arcsec B. Altieri

16. 3C58 results for MOSs Model: constant[1]*wabs[2]( powerlaw[3] ) ? M. Kirsch • flux variation off axis reduced from ± 10 % down to ± 1-2 % for both MOSs • pn to be checked with Coma/G21.5-09 observations M. Kirsch

17. missing/finding the gap • in order to recover properly the flux sources should not fall onto CCD gaps • also the condition of the right off axis angle must be taken into account • 8 observations have been optimised for that • ....one not enough

18. absolute timing accuracy news in Proc. SPIE 5165Timing accuracy and capabilities of XMM-Newton M. G. F. Kirsch1), W. Becker5), S. Benlloch-Garcia4), F. A. Jansen2) , E. Kendziorra4), M. Kuster5), U. Lammers2), A. M. T. Pollock1), F. Possanzini3), E. Serpell 3), A.Talavera1)

19. th. absolute accuracy OBT 50 s • theoretical upper limit for absolute time uncertainties is <100 s • the limited number of analyses conducted so far indicated in the past that the actual error is larger (~1ms) UTC 30 sorbit prediction 100 s 20 s XMCS EPIC-pn +- 10 s quadrantclocks quadrantclocks quadrantclocks quadrantclocks

20. a. accuracy: the bug (for details see Kirsch et al. Proc. SPIE 5165) • wrongly corrected CDMU delay (626.17 s) • delay was erroneously subtracted instead of added --> shift of 1252.34 s. • correction will be implemented in new time correlation • work around will be issued on XMM-Newton-SOC pages UTC(OBT) = ERT +(CDMU) - (Flight) - (G/S)

21. absolute timing with the Crab (for details see Kirsch et al. Proc. SPIE 5165) • absolute timing accuracy: ~300-600 s • in agreement with Crab observations performed by RXTE and Chandra • opportunity to contemporaneously observe the Crab with Chandra and in the optical using an MPE developed fast photometer to get a radio-ephemeris independent phase solution between the optical and X-ray pulses in REV: NRCO scheduled Rev 696 2003-09-28T04:17:05

22. EPIC data anomalies (for details see Kirsch et al. Proc. SPIE 5165) • pn-AUX data anomalies : • frequency of occurrence is varying • unrelated to camera mode, observing time and/or duration • random negative or positive jumps in FTCOARSE not found occasionally by SAS W. Becker pulse peak broadening, phase shift spurious pulse components M. Kirsch SAS 6.0 (winter 2003 ? ): refined detection/correction algorithm --> all problems will reliably found and corrected