m. pilar esquej, xmm-newton european space astronomy centre page 1 status of the xmm-newton slew...
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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Status of the XMM-Newton Slew Survey
P. Esquej, R. Saxton, B. Altieri, A. Read, M. Freyberg, D. Bermejo, V. Lazaro
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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Outline
Overview Processing challenges
Attitude reconstruction and positional accuracySpurious sourcesExtended sources
Conclusions
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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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
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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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)
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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Current Status
2005 2010 2015
Equivalent fraction of sky covered
15%
(20)*
45%
(55)
80%
(~100)
Number of sources
4000
(5500)
12000
(15000)
20000
(25000)
Completeness
* Including high background slews
- 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) 4178 sources in total (0.2-12 keV) bandband2750 sources in soft (0.2-2.0 keV) 2750 sources in soft (0.2-2.0 keV) bandband844 sources in hard (2.0-12.0 keV) 844 sources in hard (2.0-12.0 keV) bandband
Source density: ~0.65 sources per Source density: ~0.65 sources per square degreesquare degree
~56% have RASS counterpart within 60 arcsec
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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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
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Astrometry: initial comparisonAstrometry: initial comparison
Comparison with ROSAT survey positions shows a wide distribution, with a tail up to 1 arcmin
Two types of positional error
(1) Real error of ~15″
(2) Error of 0-60″ (mean 30″)
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Attitude Problem: correctionAttitude Problem: correction
Two types of positional error
(1) Real error of ~10″
(2) Error of 0-60″ (mean 30″) but only in slew direction
Slew direction
AB Dor
‘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
Optimal attitude file: RAF subtracted by 0.75 s from every entry
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M. Pilar Esquej, XMM-M. Pilar Esquej, XMM-NewtonNewtonEuropean Space Astronomy CentreEuropean Space Astronomy Centre
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Achieved astrometric accuracyAchieved astrometric accuracy
RASS : 15” (1) SIMBAD : 8” (1)
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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?
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Extended vs point-like sources
FF mode point sources are fitted well by a PSF, e.g. source 4
Low background and tight PSF gives good sensitivity to extended sources
Enough counts to detect extension in brightest sources
Point-like source
Extended source
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Example of extended sources
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Comparison ROSAT / XMM-NewtonComparison ROSAT / XMM-Newton
Mean count rate ratio XMM/ROSAT ~ 10
We can study source variability
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XMM-Newton Slew 1(XMMSL1)
Aitoff projection
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ConclusionsConclusions 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