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Status of the XMM- Newton Slew Survey

Status of the XMM- Newton Slew Survey. P. Esquej, R. Saxton, B. Altieri, A. Read, M. Freyberg, D. Bermejo, V. Lazaro. Outline. Overview Processing challenges Attitude reconstruction and positional accuracy Spurious sources Extended sources Conclusions. Overview.

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Status of the XMM- Newton Slew Survey

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  1. Status of the XMM-Newton Slew Survey P. Esquej, R. Saxton, B. Altieri, A. Read, M. Freyberg, D. Bermejo, V. Lazaro

  2. Outline • Overview • Processing challenges • Attitude reconstruction and positional accuracy • Spurious sources • Extended sources • Conclusions

  3. Overview - PN exposures in Medium filter in FF, eFF and LW modes • Open-slew speed = 90 degrees / hour, i.e. on-source time ~14 secs • Very low background of average ~0.1 c/arcmin2 • Area covered to date ~6300 deg2 (~15% of sky) ecliptic coordinates

  4. Processing strategy • Slew data processing using a small s/w change (available in SAS 6.5) • Tangential projection not valid over whole slew. Divide slew into 1 deg2 images and recalculate sky positions. • Source search using near-standard pipeline eboxdetect/emldetect combination tuned for ~zero background. • Use sources with DET_ML>10 (equivalent to 3.9 ) • Search independently in three bands and produce three catalogues : • soft (0.2-2 keV) • hard (2-12 keV) • total (0.2-12 keV)

  5. Current Status - Initial processing of 424 slews (FF, eFF or LW) – 25% have high background - Images & exposure maps created and source searched for 220 slews giving 4178 sources in total (0.2-12 keV) band 2750 sources in soft (0.2-2.0 keV) band 844 sources in hard (2.0-12.0 keV) band Source density: ~0.65 sources per square degree ~56% have RASS counterpart within 60 arcsec Completeness * Including high background slews

  6. Attitude Reconstruction • Crucial in determination of source coordinates • Provided by the AOCS: a star-tracker operates in adition with the Sun-sensor provide the information for reconstructing the astrometry (1 arcsec for pointed observations) • Two types of attitude data can be used during event file processing: Raw Attitude File (RAF) and Attitude History File (AHF) - Different in slew observations than that used for pointed observations

  7. Astrometry: initial comparison Two types of positional error (1) Real error of ~15″ (2) Error of 0-60″ (mean 30″) • Comparison with ROSAT survey positions shows a wide distribution, with a tail up to 1 arcmin

  8. Attitude Problem: correction Optimal attitude file: RAF subtracted by0.75 s from every entry Two types of positional error (1) Real error of ~10″ (2) Error of 0-60″ (mean 30″) but only in slew direction AB Dor Slew direction •  ‘Error ellipse’ around source (slew-oriented) • Good relative astrometry: ~15 arcsec, but poor absolute astrometry: ~30 arcsec • Systematic shift was evidenced, traced to : • quantisation of time to 1 second in AHF • timing error in the RAF, due to a delay of 0.75s of the star tracker CCDs leading to a systematic offset

  9. Achieved astrometric accuracy RASS : 15” (1) SIMBAD : 8” (1)

  10. Spurious sources • Detector flashes: due to low-energy events • Within extended or within halo of bright source: look for images with high number of sources • High background images: spurious detections due to localised background flares • Position suspect: several cases • False detection: background related?

  11. Point-like source Extended source Extended vs point-like sources Low background and tight PSF gives good sensitivity to extended sources FF mode point sources are fitted well by a PSF, e.g. source 4 Enough counts to detect extension in brightest sources

  12. Example of extended sources

  13. Comparison ROSAT / XMM-Newton Mean count rate ratio XMM/ROSAT ~ 10 We can study source variability

  14. XMM-Newton Slew 1(XMMSL1) Aitoff projection

  15. Conclusions • 220 slews source-searched (using best strategies): • 4013 sources (after removing spurious sources) • Sky coverage: ~6300 deg2 (~15% of sky) • ~0.65 sources per square degree • XMM-Slew positional accuracy ~8″ • Soft X-ray band detection limit close to ROSAT BS catalogue • Hard X-ray band detection limit deepest ever: • > 10 × deeper than EXOSAT, HEAO-1 • ~ 2.5 × deeper than RXTE (only has 1° positional accuracy) • Topics under current investigation: optical correlation, refinement of spurious detection, source extension strategy, recovering science from high-background slews, source variability • Aim to issue first slew source catalogue (XMMSL1) before end of 2005 • Provide an upper limit server in 2006

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