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A look at XMM slew data

A look at XMM slew data. Richard Saxton, Andrew Read, Michael Freyberg, Bruno Altieri, Puri Munuera. What have we got ?. 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

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A look at XMM slew data

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  1. A look at XMM slew data Richard Saxton, Andrew Read, Michael Freyberg, Bruno Altieri, Puri Munuera

  2. What have we got ? • 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 • Closed slew, open slew, closed slew. Open slew speed = 90 degrees / hour, i.e. on-source time ~15 secs • Area covered ~8000 deg2 (~20% of sky)

  3. Possible problems • We could use the time usefully for closed-cal observations (MOS needs more exposure time as CAL source gets weaker) • Only 15 secs on-source exposure time • Bright stars may cause false detections due to optical loading • Earlier surveys may have already done the science, e.g. ROSAT • High background may hide sources

  4. Pilot study of 11 slews SAS worked fine after small OAL change. Tangential projection isn’t valid over the entire slew. Long slews need to be subdivided to maintain the astrometry.

  5. Pilot study of 11 slews SAS worked fine after small OAL change. Tangential projection not valid over whole slew. Long slews need to be subdivided to maintain astrometry. Divide into 1 deg2 images and recalculate sky positions Source search using standard pipeline eboxdetect/emldetect combination tuned for ~zero background.

  6. Pilot study of 11 slews SAS worked fine after small OAL change. Tangential projection not valid over whole slew. Long slews need to be subdivided to maintain astrometry. Divide into 1 deg2 images and recalculate sky positions Source search using standard pipeline eboxdetect/emldetect combination tuned for ~zero background.

  7. Initial impressions MOS PN PN Source extended into a 4 arcmin streak due to 2.6 second frame time Full frame mode streak = 6 arcsecs – not noticeable Extended full frame 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 Filter pn events with FLAG=0, PATTERN<=4, PI>200

  8. PROCESSING SUMMARY Had to exclude two high(er) background slews which produced many spurious sources. One may still be useful by tuning search params. Source searched images from 9 pn slews and found 139 sources down to det_ml=10, ~0.5 source/deg2 All 139 sources eyeballed and look ok, i.e. no obvious false detections due to background effects. Minimum number of counts = 6 giving detection limits of F0.2–2 = 1.0x10-12, F2-10 = 1.6x10-12 ergs s-1 cm-2

  9. Flux limits Rosat limit = 5x10-13 (92% of sky) EMSS = 5x10-14 – 3x10-12 (2% 0f sky) (0.3-4) HEAO-1 survey = 6x10-12 – 3.6x10-11 (all-sky) Exosat slew survey = 5x10-11 (n% of sky) RXTE ASM = 7x10-10 (2-10)

  10. Optical loading assessment DSS images with 20” error circle DSS on slew positions + 1hour RA 18 sources coincident with bright stars – an issue but not dominant

  11. X-corr with ROSAT RASS bright source cat = 42 RASS faint source cat = 21 Brightest slew source Faintest slew source

  12. Identifications Total sources = 139 ROSAT survey IDs = 63 10 bright stars, non-RASS sources 8 sources with NED counterparts but consistent with null hypothesis 1 source observed twice in separate slews 2 sources seen in ROSAT pointed obs. and not in RASS (14 not seen in either). 55-63 unidentified

  13. The non-RASS sources 1 : funnies Sources 1 and 3 are Extended and at edge of FOV Caused by Crab ~10 arcmins from edge of slew Unexplained streaks in celestial coordinates. Other satellites ? Cosmic rays ? These produce 5 false sources

  14. The streak sources Detector map shows events Confined to 1 CCD. Events occur within 1 frame with very fast decay Very soft spectrum with a peak at 100 eV and secondary peak at 240 eV Affects one CCD so must be detector related

  15. The non-RASS sources 2 : other spurions Source 9 seems to be a source detection algorithm problem

  16. Galactic location After removal of spurious sources 55 non-ROSAT sources remain Many lie at low Galactic latitude A few have low RASS exposures Need to do ROSAT upper limits analysis and find XMM hardness ratios

  17. Extended source analysis FF mode point sources give a good fit to PSF, e.g. source 4 Source 2: 2x2 arcmin The 20 brightest sources - 5x5 arcmin images • Enough counts to detect extension in brighter sources

  18. Known clusters: Abell 3581 (EFF mode) Slew direction Source 5 • Easily detected as extended in 15 second exposure

  19. Conclusions • Analyse Epic-pn slew data and put MOS in CAL Closed • ~10% of sources caused by optical loading • High background affected 1-2 out of 11 slews • Expect to find ~ 5,000 sources from current data • Sensitive to extension in brighter sources • Soft band detection limit ~2 times RASS limit • Deepest 2-10 keV “all sky” survey to date at 1.6x10-12 • Possibility of finding Galactic plane sources missed by Rosat • Useful for checking long term variability • Work to be done on unidentified sources

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