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The XMM-Newton Slew Survey

The XMM-Newton Slew Survey. Andrew Read. Richard Saxton, M. Pilar Esquej Michael Freyberg, Bruno Altieri. Overview. - 390 slew datasets in archive - PN, MOS-1/2 exposures in Medium filter with the observing mode set to that of previous pointed observation

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The XMM-Newton Slew Survey

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  1. The XMM-Newton Slew Survey Andrew Read Richard Saxton, M. Pilar Esquej Michael Freyberg, Bruno Altieri

  2. Overview - 390 slew datasets in archive - PN, MOS-1/2 exposures in Medium filter with the observing mode set to that of previous pointed observation - Average slew length is 70 degrees - Data available for slews > 30 mins - Closed slew, open slew, closed slew. Open slew speed = 90 degrees / hour, i.e. on-source time <~14 secs - Area covered to date ~8000 deg2 (~20% of sky)

  3. Pilot study 1: To check if slew data scientifically useful Process 9 slews, source searching single 0.2-15 keV image (flag=0, pattern<=4), flat exposure map SAS worked fine after small OAL change. Tangential projection not valid over whole slew. Long slews need to be subdivided to maintain astrometry. Divide slew into 1 deg2 images and recalculate sky positions Source search using near-standard pipeline eboxdetect/emldetect combination tuned for ~zero background.

  4. Initial impressions PN (eFF) MOS PN Slew direction Source extended into a 4 arcmin streak due to 2.6 second frame time Full frame (73ms) mode streak = 6 arcsecs – not a problem Extended full frame (200ms) streak of 18 arcsecs Extra pn sensitivity + additional MOS background means little to be gained from analysing MOS slews Epic-pn attitude reconstruction very good

  5. Optical Loading Assessment DSS images of 139 pilot#1 slew positions DSS on slew positions + 1hour RA ~10% sources coincident with bright stars - Optical loading or genuine X-ray sources? - Could be an issue but not dominant

  6. Spurious Sources… Sources 1 & 3 of Pilot#1 … due to crab off-axis !

  7. Pilot Study 1: Summary Source searched images from 9 pn slews and found 139 sources down to det_ml=10, ~0.5 source/deg2 Identifications Total sources = 139 ROSAT survey IDs = 63 Bright stars (optical loading?), detector flashes, Crab off-axis & spurions + 1 source observed twice in separate slews leave… ~50 unidentified

  8. Extended source analysis Source 2: 2x2 arcmin Pilot#1 sources - 5x5 arcmin images FF mode point sources are fitted well by a PSF, e.g. source 4 Enough counts to detect extension in brightest sources

  9. Abell 3581 (EFF mode) Slew direction Easily detected as extended in <~14 second exposure

  10. Conclusions from pilot 1 - MOS slew data effectively useless - ~10% of sources coincident with bright stars - optical loading? - Expect to find ~ 4,000 sources from current data - Sensitive to extension in brighter sources New operations strategy (now in place): • MOS slews used for calibration • All PN slews larger than 15 minutes down-linked and processed • Medium filter if FF,eFF,LW and Closed for other modes

  11. Pilot study 2: To investigate optimum processing and source search strategy Three long slews ~ 110 degrees, 1 each of FF, EFF and LW modes 3 source-searching strategies investigated A) 1XMM scheme - separate 0.2-0.5, 0.5-1.0, 1.0-2.0 and 2.0-12.0 keV images – 23 detections (mean of 14.4 counts) B) Search single 0.2-12 keV, pattern<=4 image – 110 detections, many spurious C) Search 0.2-0.5 (pattern 0) + 0.5-12.0 (patt <=4), single image - 64 detections (mean of 8.6 counts) Best results from scheme C: we lose band-specific count rates and hardness ratios but can calculate these a posteriori with eregionanalyse on individual images. Also almost all spurious detector features removed (using only singles in very softest band)

  12. Usage of Exposure Maps Slew searched using variable exposure maps and detector mask – no unusual effects. Next to last degree of slew Final degree of slew Uneven exposure at end of slew due to closed-loop.

  13. Conclusions from pilot 2 • Source density again ~0.5 / deg² • Use full-band image: • 0.2-0.5 (patt=0) + 0.5-12.0 keV (patt<=4) • & soft-band (~ROSAT) image: • 0.2-0.5 (patt=0) + 0.5-2.0 keV (patt<=4) • & hard-band image: • 2.0-12.0 keV (patt<=4) • i.e. 3 Surveys • - Use exposure maps and detector masks - Find individual sub-band count rates after source search - Only use FF, EFF and LW mode data - For uniform survey can apply an exposure threshold

  14. The XMM Slew Survey : current processing scheme - Processing of slew data (creation of event files) - Creation of images, exposure maps (full-, soft- and hard-band) - Source search full-, soft- and hard-band images using exposure maps - Make catalogue of detections - Make DSS images for each detection - Check for and flag spurious sources - Check for and flag optical loading due to bright stars - Find hardness ratios from individual band images - Make clean catalogue of sources - Cross-correlate with Rosat - Cross-correlate with other catalogues (In preparation…) - Analyse extensions - Co-add slews and re-search - Optical follow-up…

  15. Current Status - Initial processing and event file creation for all available Slews - 374 Slews: 297 of which are FF (206), eFF (61) or LW (30) - 54 Slews: Images & exposure maps created & source-searched (31 FF, 19 eFF, 4 LW) - Slew catalogue frozen (01/04/05) - 780 sources in total (0.2-12.0 keV) band - 645 sources in soft (0.2-2.0 keV) band - 96 sources in hard (2.0-12.0 keV) band - At faint end, - 68 soft-band sources, not detected in the total band - 20 hard-band sources, not detected in the total band - Total of 868 sources in ~1800 deg² ~0.5 sources per square degree Currently searched slews

  16. Current Problems - Processing problems affect ~40% of slews – Concentrating at present on slews which process correctly first time – Finding solutions to particular problems as we progress - Some slews contain sections with high exposure, related to the closed-loop slew phase. Sub-Images with large exposures are excluded at present - High background slews (~25%) are excluded at present - from 297 FF, eFF, LW slews, we are initially processing 219 and expect to find ~3600 sources - but, we can probably recover a lot of the high background slews by subsetting the data using GTIs

  17. UY Vir Total band (0.2-12 keV) DSS Image 2’×2’ Blue circle in X-ray image indicates a detection Soft band (0.2-2 keV) Hard band (2-12 keV) (RASS src)

  18. Mrk 352 ESO443-IG005 MCG 04-53-021 NGC5899 Four Galaxies Non-RASS

  19. Two Merging Galaxy Pairs NGC 4748 II Zw 742

  20. Faint sources detected in soft/hard-band but not in full-band Soft source not detected in full energy band Hard source not detected in full energy band Extra background in full-energy band (sometimes just 1 photon!) can flip statistics below the threshold (DET_ML=10)

  21. Sources detected in separate slews • - Source detected in 3 separate slews: • Rev 0570, Rev 0573, Rev 0574 • Known ROSAT source (+faint galaxy) • Evidence for variability (factor ~2)

  22. Well Known Sources N132D (4.1″ pixels)

  23. Extremely Bright Sources 1RXS J134143.6-165736 LMXRB RASS~145 ct/s Pseudo-MIPs (e.g. 2 ~9keV Photons/pixel in a frame) LW mode

  24. … and other oddities… • Southern source - RASS • Northern source – non-RASS

  25. Optical Loading – A Problem? • Stars in Slew 0.2-2.0 keV counts Medium Filter V Magnitude -No correlation between source counts and Vmag for bright stars - Consistent with optical loading predictions: 5 counts expected above 200eV only for stars brighter than V=3.75 • CD 36-1289 : • X-ray emission from this V=10.5 star, but nonefrom neighbours at V=6.5 and V=7.6 • Several examples like this • No optical loading problems – Genuine X-ray sources

  26. Correlations with 2MASS Blue squares: Number of 2MASS sources vs. distance to slew source Green diamonds: Equivalent distribution for random sky positions (same number of sources) Red triangles: Difference in distributions i.e. Blue minus Green Pointing accuracy of Slew survey ~6″ … but long tail…?

  27. Correlations with ROSAT • 407 Slew source matches with ROSAT BSC & FSC out to 120″ • Distribution of distance offsets shown • Small error (includes RASS error), but long tail…?

  28. Attitude Problem Two types of positional error (1) Real error of ~6″ (2) Error of 0-60″ (mean 30″) but only in slew direction Likely due to the current ATS attitude file having only 1sec time resolution AB Dor Slew direction ‘Error ellipse’ around source (slew-oriented) Optimistic we can remove error (2) by re-processing the attitude data (RAF?) Error (1) remains, but easily small enough to allow good optical follow-up Also may be cause of patterns in exposure maps

  29. Correlations with ROSAT • RASS count rate versus XMM Slew count rate for 407 matches • Line shows 10:1 factor • ~45% of Slew sources with <5cts are RASS sources • - comparable with whole sample

  30. Correlations with ROSAT All Slew sources: Hardness ratio vs Galactic latitude Green circles: No RASS counterpart Red crosses: RASS counterpart Hard sources not seen by ROSAT RASS sources on average softer than non-RASS sources Hardness

  31. Correlations with ROSAT All Slew sources in Galactic coordinates Green circles: RASS counterpart Red crosses: No RASS counterpart No obvious trend

  32. Survey Characteristics Source Count Distribution Exposure Time Distribution Minimum @ ~ 4 counts Maximum @ ~ 10 seconds - Can calculate flux limits for the XMM-Slew survey

  33. Flux limits RASS 5.0x10-13 (92% of sky) EMSS 3.0x10-12 (2% 0f sky) HEAO-1 3.6x10-11 (all-sky) Exosat 5.0x10-11 (?% of sky) RXTE 1.0x10-11 (all-sky), but with only 1° positional accuracy

  34. Schedule - Initial processing of slew data(finished) - Creation of images, source searching, rejection of spurious sources(Feb to May) - Cross correlation with ROSAT, other catalogues, DSS, SDSS etc. (Apr to July) - Creation of final catalogue for ingestion into XSA (Aug to Sep) - Ingestion into XSA (end of September) - Investigate extended sources (begin May) - Search co-added slews (TBD) - 2 new (ESAC) trainees, Diego Bermejo, Veronica Lazaro, recently started on project Now

  35. Conclusions from current Slew analysis - All available (374) Slews processed (~20% of sky) (Revs 314-785, → 100% of sky by mid-2014) - 54 Slews source-searched to date (using best strategies): 868 sources found in 1800 deg² (~4.5% of sky) ~0.5 sources per square degree - Soft X-ray band detection limit close to ROSAT All-Sky Survey - Hard X-ray band detection limit deepest ever: > 10× deeper than EXOSAT, HEAO-1 ~ 2.5× deeper than RXTE (only has 1° positional accuracy) - XMM-Slew positional accuracy ~6″ Additional ‘attitude-error’ (30″ mean), but only along slew Confident that this attitude-error can be drastically reduced - Aim to recover science from high-background slews - Encountering & solving problems en route – Still on schedule…

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