EPIC Background Template Files

1. EPIC Background Template Files • Why we need them - previous attempts insufficient • Adding together high galactic latitude files - choices & screening • Comments on the internal background in MOS • Using the files astrophysically - seem consistent with ROSAT/ASCA and other historic data • Future developments - SAS task needed ? D Lumb -- SCI-ST. EPIC TTD Nov01

2. Context • Extended objects are an important field of XMM science • Background surface brightness relatively high and variable need a good estimate of background which does not rely on the in-field subtraction • “Band-aid” background files provided for A&A special issue analysis (using Lockman Hole and selected calibration fields) • S:N too low, heterogeneous field selection (NH, filters), also the exposure corrections uncertain for use D Lumb -- SCI-ST. EPIC TTD Nov01

3. Field Choice & Locations • Chose all THIN filter (most extended objects use THIN & easier to make a change for other filters if homogeneous data set has been employed) • High galactic latitude away from any obvious features in the halo or near bright point sources • Low proton background, low NH, long observations from calibration, PV or SOC data sets where possible to minimise data rights issues • If a typical GO observation is ~30ksecs, then aim for 10 times this for a reasonable signal:noise D Lumb -- SCI-ST. EPIC TTD Nov01

4. Field Locations (contd.) RA Dec Date Time N_H L II BII 2000 (ks) (1020) 02:18:00 -05:00:00 2000-07-31 60 2.5 169.7 -59.8 02:19:36 -05:00:00 2000-08-04 60 2.55 170.35 -59.5 02:25:20 -05:10:00 2001-07-03 25 2.7 172.3 -58.6 02:28:00 -05:10:00 2001-07-06 25 2.7 173.5 -58.2 10:52:44 +57:28:59 2000-04-29 70 0.56 149.3 53.1 12:36:57 +62:13:30 2001-06-01 90 1.5 125.9 54.8 13:34:37 +37:54:44 2001-06-23 80 0.83 85.6 75.9 22:15:31 -17:44:05 2000-11-18 55 2.3 39.3 -52.9 D Lumb -- SCI-ST. EPIC TTD Nov01

5. Source Extraction • Need to remove bright sources, but as lots of the XMM background normally gets resolved, we cannot remove ALL or it is not representative for the observer’s field! • By co-adding several fields there is some dilution effect, and as long as it is OK on ~arcminute levels and << 10-14 ergs source level, it will probably cover most eventualities • Avoid arbitrary manual removal, so used EBOXDETECT (0.5-2keV, local mode only), noting ~ 10 brightest locations and excise from 50 arcsec diameter (>~80% flux each) • Based on LogN-LogS this cut must be ~1.5 x 10-14 ergs, which after dilution >5 means only very faint effective residual (confirm by manual inspection) point source content D Lumb -- SCI-ST. EPIC TTD Nov01

6. File Creation • Screening of proton flares (PI>10000&&PATTERN==0) at 4s in 100 sec time bins (if screening is too tight may not match observers’ cuts) • Concatenate the event list in time, apply exposure extensions from original files (also concatenated), badpix, offset, GTI extensions left in • Hide identity of original fields , modify keywords to be homogenous and consistent (START, STOP, FRACEXP, LIVETIME etc.) • Basic duration now >400ksec, but observer might consider further screening to match own data set which now should be possible as extensions are coherent (I think that 350ksec is closer to usable quiet duration) D Lumb -- SCI-ST. EPIC TTD Nov01

7. What does it look like? • DETX,DETY coords, MOS1 & PN (E>250eV) D Lumb -- SCI-ST. EPIC TTD Nov01

8. MOS Al & Si • Al weaker around edge of centre CCD, Si is reverse D Lumb -- SCI-ST. EPIC TTD Nov01

9. PN Cu & Soft band • Metal emission lines with central hole • Soft band dominated by streaks D Lumb -- SCI-ST. EPIC TTD Nov01

10. MOS Internal Background • Can use the substantial area outside filter to determine the true internal background component • Flat spectrum above 1keV, count rate consistent with CR rate and 99.5% rejection • Steeply rising low energy background – worse in MOS2 than MOS1 – correlated with the bad and flickering pixels? • Al and Si emission lines variable so cannot use as simple subtraction for an IN-FIELD. Choose a model of several Gaussians and broken power law • Use this as a “background” component for in-field but change normalisations according to surface area, but allow emission line intensities to be free parameter D Lumb -- SCI-ST. EPIC TTD Nov01

11. MOS Internal Background Al Au Si & Au Cr, Mn Fe D Lumb -- SCI-ST. EPIC TTD Nov01

12. Astrophysical Analysis • With a high signal:noise and reasonable internal background characterisation we can attempt astrophysical analysis. • Produce focal plane vignetting averaged response file and fit MOS1 & MOS2 simultaneously • Extragalactic power law seems consistent (harder than 1.4 unless the bright sources put back in) – but careful analysis of the out of field scattered component and the cosmic variance to brighter sources may allow a resolution to the long-standing background normalisation problem • Soft component temperature models are consistent with Kuntz&Snowden analysis, but the LHB components poorly constrained (calibration problems) D Lumb -- SCI-ST. EPIC TTD Nov01

13. Future Development • Could produce further additions for deeper fields? • Need to fix for filters and galactic location, possibly even CR variations: • A task can be envisaged 1) Takes the model for internal component scaled by CR rate proxy 2) Produce soft component based on ROSAT multi-band analysis for the appropriate LII & BII (Steve Snowden working on tool) 3) Filter choice then added through the appropriate response matrix 4) Proton screening still a problem? D Lumb -- SCI-ST. EPIC TTD Nov01