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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 & initial impression about the XMM-Newton slew observations Data processing & source searching strategy: current status

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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 & initial impression about the XMM-Newton slew observations • Data processing & source searching strategy: current status • Attitude reconstruction and positional accuracy • Spurious sources • Extended sources • Sensitivity • Small sample of detected sources • Conclusions

  3. Overview • XMM-Newton performs slewing manoeuvers between targets with the EPIC cameras open and the other instruments closed • PN, MOS-1/2 exposures in Medium filter with the observing mode set to that of previous pointed observation • Open-slew speed = 90 degrees / hour, i.e. on-source time ~14 secs • Area covered to date ~6300 deg2 (~15% of sky) • 465 slew datasets in archive (since Rev 314) • Data initially available for slews longer than 30 minutes • Average usable slew length is ~60 degrees ecliptic coordinates

  4. Initial impressions MOS New operations strategy (from end of 2004): - MOS slews will be used for calibration - All PN slews longer than 15 mins will be down-linked and processed and used for science: XMM Slew Survey - Medium filter if FF, eFF, LW and Closed for other modes • Source appearance depends on the frame time of the observing mode • MOS cameras: spread source into a 4 arcmin streak • pn camera: source extension less than 18 arcsec PN Very low background of average ~0.1 c/arcmin2 due to the low exposure time. But some slews taken in time of enhanced solar activity exhibit high background giving rise to spurious sources

  5. 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)

  6. 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

  7. 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

  8. 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

  9. Attitude Problem: correction Optimal attitude file: RAF subtracted by 0.75 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

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

  11. Spurious sources • Detector flashes: avoided by only using single pattern below 0.5 keV • Within extended or within halo of bright source: can be spotted looking 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?

  12. 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

  13. Example of extended sources Abell 3581 2 SNRs in SMC Easily detected as extended in 14 second exposure

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

  15. X-ray All-Sky Surveys : 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 (98% of sky) • RXTE: 1.0x10-11 (all-sky), but with only 1° positional accuracy XMMSL1: 6(4.5) 10-13 ergs s-1 cm-2 in the soft band (0.2-2.0 keV) 4(3) 10-12 ergs s-1 cm-2 in the hard band (2-10 keV)

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

  17. Correlations Slew-soft with ROSAT Mean XMM/ROSAT ~ 10 We can study source variability ROSAT XMM soft

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

  19. Merging Galaxy Pairs NGC 4748 II Zw 742

  20. More sources... Several LMXB at few hundred c/s N132D

  21. 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 • Aim to issue first slew source catalogue (XMMSL1) before end of 2005 • Provide an upper limit server in 2006

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