1. The MOS Background (and XMM-ESAS)‏ K.D. Kuntz The Henry A. Rowland Dept of P&A Johns Hopkins University And occasionally GSFC With PN additions from S.L.Snowden GSFC

2. Overview Review of the Goddard/ESAS method Update on instrument/detector evolution (a purely phenomenological approach)‏ Future updates & automation A few notes about the PN from SLS

3. Method Review: Philosophy Emission from the Galactic ISM fills the FOV –Sufficiently faint that it must be summed over large regions in order to produce a good spectrum The same is true of extended extragalactic emission (e.g. galaxies & clusters)‏ Background subtraction method must provide good statistics over large regions of the FOV And still be sensitive to the small-scale spatial/temporal variations in the detector

4. Method Review The corner pixels are a measure of the particle background

5. Method Review The corner pixels are a measure of the quiescent particle background (QPB) for a given observation There are not enough counts in the corner pixels of a single observation for a robust characterization of the background…so Measure the rate and hardness ratio for your observation and then… Augment with corner spectra from other obsids that have the same rate and hardness ratio

6. Method Review Rate: 0.3-10.0 keV Hardness: 2.5-5.0/0.4-0.8 keV

7. Method Review The corner pixels are a measure of the quiescent particle background (QPB) for a given observation There are not enough counts in the corner pixels of a single observation for a robust characterization of the background…so Measure the rate and hardness ratio for your observation and then… Augment with corner spectra from other obsids that have the same rate and hardness ratio

8. Method Review From a collection of all corner pixel spectra, extract those with similar ratees and hardnesses with an accumulated exposure time of at least X seconds, where X~10 6 s

9. Method Review The corner pixels are a measure of the quiescent particle background (QPB) for a given observation There are not enough counts in the corner pixels of a single observation for a robust characterization of the background…so Measure the rate and hardness ratio for your observation and then… Augment with corner spectra from other obsids that have the same rate and hardness ratio

10. Method Review The corner pixel spectrum is not representative of the QPB spectrum within the FOV The filter-wheel-closed (FWC) data do not reflect the obsid-to-obsid variation Assume that overall changes in spectral shape seen in the corner pixel data are reflected in the FWC data FOV = FWC*observed corner/FWC corner

11. Method Review Method seems to work reasonably well… …yielding good repeatability

12. Method Review Must maintain up-to-date –Databases of corner pixel spectra –Databases of FWC images (in particular we need to make sure we continue to accumulate new FWC data)‏ “Eternal vigilance” for instrumental changes –Ensure that method remains valid

13. Current QPB Update Using all obsids public before September 2008 Removed all time intervals with Soft Proton (SP) flare contamination Removed all obsids with clean time < 5 ks

14. Current QPB Update 2-7 1-7 2-6 1-6 2-5 1-5 2-4 1-4 2-3 1-3 2-2 1-2

15. 2-7 1-7 2-6 1-6 2-5 1-5 2-4 1-4 2-3 1-3 2-2 1-2

16. Current QPB Update Evolution of rate: upward since ~Rev 725 Evolution of hardness: slightly downward Epoch 0 Epoch 1Epoch 2

17. Current QPB Update Compare spectra with 3<HR<4 for three epochs Results consistent for MOS1-2,3,6,7 MOS2-2,3,4,6,7 Minor differences for E<0.3 keV

18. Anomalous States Some chips have intermittent states where the QPB spectrum is very different Usually characterized by high Rs and low HRs

19. Current QPB Update Chips with anomalous states show strong evolution in Rate-Hardness diagram

20. Current QPB Update Chips with anomalous states show strong evolution in Rate-Hardness diagram What happens to the spectra?

21. Current QPB Update

24. MOS 2-5 –Currently in anomalous state for the bulk of time –Spectral shape stable – but very strong MOS 1-5 –Incidence of anomalous states currently low –Spectral shape unstable MOS 1-4 –Currently in anomalous state for ~50% of time –Spectral shape unstable Data from chips in anomalous states should probably be discarded for low surface brightness studies Spectral shapes in non-anomalous times stable Will need to re-write descriptions for anomalous states

26. Future QPB Updates Past Construction –Filtered out periods with strong SP flares (~espfilt)‏ –Hand selection of obsids for inclusion Current Construction (not yet released)‏ –Filtered out periods with strong SP flares –Selection of obsids Histogram Center < 4 Histogram Width < 0.175 Cleaned exposure time > 5 ks –Roughly reproduces by-hand process

27. Future QPB Updates Future construction –Must use automatic selection of obsids –Use parameters describing “good” obsids? –Rethink this process…

28. Future QPB Updates Soft Proton Flares do not affect corner data –So SP filtering is pointless and a waste of time FOV Corner

29. Future QPB Updates There is contamination of the corner data by Particle Background Excesses (PBEs?)‏ –Usually when S/C entering or exiting particle belts –Can be filtered using same routines, diff. params Corner

30. Future QPB Updates Filtering the corner data –Increases available corner data by ~1.3-1.5 –Fully automatic selection criteria –Currently being test-implemented at JHU/GSFC Corner

32. Current FWC Update MOS FWC campaign to determine whether the FWC images/spectra are temporally variable –Compare FWC data for 1130 1130 –Construct images of (post-1130/pre-1130) -1

33. Current FWC Update All 5-14 2.5-5 1-2 0.4-0.8 1S2S4S4H5S5H6S7S3S MOS1

34. Current FWC Update All 5-14 2.5-5 1-2 0.4-0.8 1S2S4S5S5H6S7S3S MOS2 Mode mixing?

35. Current FWC Update MOS1MOS2 Variation within expected range if w/o temporal var. Negative tail may be due to the increase of bad pixels

36. Current FWC Update MOS FWC campaign to determine whether the FWC images/spectra are temporally variable –Compare FEC for 1130 1130 –Construct (post-1130/pre-1130) -1 images –Compare spectra

37. Current FWC Update MOS FWC campaign to determine whether the FWC images/spectra are temporally variable –Compare FEC for 1130 1130 –Construct (post-1130/pre-1130) -1 images No significant signs of temporal variability –Compare spectra No significant signs of temporal variability Continued monitoring necessary –Every n th calclosed slew to be converted to closed

38. Future FWC Updates Difficult to make automatic –Must inspect each observation of each chip to determine whether chip in standard or anomalous state –Anomalous state definitions are evolving with time, so dependent on up-to-date inspection of corner data. Given rate at which FWC data accumulates, human interaction no big deal

40. PN in ESAS PN software nearly complete –Needs testing on additional data sets –Possible over-estimation of background –Data probably not useful below ~0.4 keV or above 7.2 keV

41. Progress on ESAS for the PN model particle background. Radial profile spectral fit of Abell 1795 using 10 annuli and a RASS spectrum.   ~1.5 for 7829 DOF

42. PN in ESAS PN software nearly complete –Needs testing on additional data sets –Possible over-estimation of background –Data probably not useful below ~0.4 keV or above 7.2 keV PN QPB (&FWC?) databases constructed –QPB shows little temporal variation PN flare vignetting images constructed

43. FINE