Clusters as calibration Clusters as calibration toolstools

S. Molendi (IASF-MI)S. Molendi (IASF-MI)

MotivationMotivation

• To what level can we trust the calibration of our instruments?

• How far can we push spectral modelling before we end up fitting instrument systematics rather than astrophysically relevant features?

The final frontier?The final frontier?

This is a frontier that is worth exploring, major future X-ray missions are not around the corner, in many respects XMM-Newton and Chandra will be the best experiments for many years to come.

Cross Cal with ClustersCross Cal with Clusters

• Has enjoyed some success• Lots of photons and no pile-up!• No need for simultaneous

observations• Spectrum is not a simple power-

law however at the level of precision we are dealing with are there any pure pl spectra in the X-ray sky?

• Background can be a limitation

The SampleThe Sample

only EPIC to be extended to Chandra16 observations of 13 objectsspectra selected to be:• Observed in thin or medium filters• high SB• 1T • 2 < kT < 8• 0.015 < z < 0.09• long exposures

WORK IN

PROGRESS

The SampleThe Sample source ring T SB Z arcmin keV erg cm2s-1amin2 Solar units ------------------------------------------------------1. 2A0335 2 5 3.2 5.0e-13 0.46 2. A85 3 5 6.0 4.5e-13 0.39 3. A262 2 4 2.2 3.0e-13 0.31 4. A478 2 5 6.5 5.7e-13 0.31 5. A496 4 7 4.5 2.7e-13 0.31 6. A1060 2 5 3.0 4.2e-13 0.46 7. A1650 1 2 5.8 4.0e-13 0.35 8. A1795 3 5 6.0 3.6e-13 0.3 9. A2029 2 4 7.6 7.5e-13 0.37 10. A2199 2 5 4.2 7.5e-13 0.44 11. A2597 2 4 3.7 8.9e-14 0.28 12. AWM7 2 4 3.7 8.7e-13 0.28 13. MKW3s 2 4 3.6 3.2e-13 0.30

BackgroundBackground

BackgroundBackground

AnalysisAnalysis

Fit spectra with 1T and 2T models In most cases no substantial

improvement with 2T, even when improvement is substantial, typically for objects with better statystics, 2T modeling is un-physical, possibly associated to systematics

CalibrationCalibration

Consider data from each camera individualy

X-ray vs radio NX-ray vs radio NHH

● MOS1● MOS2● pn

X-ray vs radio NX-ray vs radio NHH

Investigating residuals Investigating residuals

• Explore residuals in the form of ratio data/model

• Heavily regroup data (beyond resolution limit) to achieve few % errors

2A 0335 Ratio data/model2A 0335 Ratio data/model

Investigating residuals Investigating residuals

• Compute mean residuals averaged over all 16 observations

• Statistical errors are reduced, systematics should show up

Deviations from a simple Deviations from a simple thermal model thermal model

MOS 1

Deviations from a simple Deviations from a simple thermal model thermal model

MOS 2

Deviations from a simple Deviations from a simple thermal model thermal model

pn

Stability of residuals Stability of residuals

Do different objects show similar residuals?

ColdCold vsvs Hot Hot

MOS2

ColdCold vsvs Hot Hot

pn

SampleSample vsvs Perseus Perseus

MOS1

SampleSample vsvs Perseus Perseus

MOS2

SampleSample vsvs Perseus Perseus

pn

Investigating residuals Investigating residuals

• Residuals at least in some instances appear to be similar in different objects

• Spectral model 1T, hot cold, 4T for Perseus -- unlikely

• Instrument systematics

• Redistribution -- rmf

• Effective Area -- arf

pn soft band residuapn soft band residua

Centaurus

pn soft band residuapn soft band residua

Perseus

pn soft band residuapn soft band residua

Mkn 421

mos soft band residuamos soft band residua

Centaurus

mos soft band residuamos soft band residua

Perseus

Implications Implications

• Systematics likely related to rmf, particularly true for pn

• MOS less certain

De Grandi+SM 09

Cross-CalibrationCross-Calibration

Compare different instruments

MOS1 & pn NH vs MOS2 MOS1 & pn NH vs MOS2 NHNH

● MOS1● pn

MOS1 & pn kT vs MOS2 MOS1 & pn kT vs MOS2 kTkT

● MOS1● pn

MOS1,MOS1, MOS2 MOS2 && pnpn vsvs pn pn modelmodel

MOS1,MOS1, MOS2 MOS2 && pnpn vsvs pn pn modelmodel

MOS1,MOS1, MOS2 MOS2 && pnpn vsvs pn pn modelmodel

MOS1 MOS1 && MOS2 MOS2 vsvs pn modelpn model

SummarySummary

Calibration• Redistribution problem on pn• MOS, if there is one it’s smaller

Cross-calibration

• Good to 3% in 0.7-3.5 keV band

• problem with Effective areas at energy

ACIS S3 vs EPIC pnACIS S3 vs EPIC pn

• We compare Chandra ACIS S3 with EPIC pnWe compare Chandra ACIS S3 with EPIC pn• About 3×10About 3×1066 events for each spectrum events for each spectrum

extracted from annulus with bounding radii of 1' and extracted from annulus with bounding radii of 1' and 2 2 ‘‘

• Used old and new Chandra calibrations Used old and new Chandra calibrations (CALDB 4.1.1 with hrmaD1996-12-20axeffaN0008.fits)(CALDB 4.1.1 with hrmaD1996-12-20axeffaN0008.fits)

• Multi T spectral model (Molendi & Gastaldello Multi T spectral model (Molendi & Gastaldello

09)09)

ACIS S3 vs EPIC pnACIS S3 vs EPIC pn• We start from the EPIC pn spectrum We start from the EPIC pn spectrum

ACIS S3 vs EPIC pnACIS S3 vs EPIC pn• We start from the EPIC pn spectrumWe start from the EPIC pn spectrum• Perform fit with multi T modelPerform fit with multi T model

ACIS S3 vs EPIC pnACIS S3 vs EPIC pn• We start from the EPIC pn spectrumWe start from the EPIC pn spectrum• Perform fit with multi T modelPerform fit with multi T model• Fold best fitting model with ACIS Fold best fitting model with ACIS

response and compare it with ACIS response and compare it with ACIS spectrumspectrum

ACIS S3 vs EPIC pnACIS S3 vs EPIC pnPlot residuals in the form of ratio data/modelPlot residuals in the form of ratio data/model

Renorm applied to match spectra at 1.5 keV Renorm applied to match spectra at 1.5 keV

pnpn

ACIS S3ACIS S3

ACIS S3 vs EPIC pnACIS S3 vs EPIC pnPlot residuals in the form of ratio data/modelPlot residuals in the form of ratio data/model

Renorm applied to match spectra at 1.5 keV Renorm applied to match spectra at 1.5 keV

pnpn

ACIS S3ACIS S3

ACIS S3 vs EPIC pnACIS S3 vs EPIC pnSimilar result when using a different region Similar result when using a different region

Annulus with Annulus with bounding radii of 2' and 3 ‘bounding radii of 2' and 3 ‘Showing only plot with new ACIS calibrations

pnpn

ACIS S3ACIS S3

Cross CalCross Cal

pn and ACIS S3 spectral shapes are pn and ACIS S3 spectral shapes are now in much better agreement! now in much better agreement!

Differences are almost everywhere Differences are almost everywhere less than ~5%less than ~5%

Major discrepancy in 0.7-1.0 keV Major discrepancy in 0.7-1.0 keV rangerange

ACIS S3 vs EPIC pnACIS S3 vs EPIC pnResiduals in the form of ratio data/modelResiduals in the form of ratio data/model

Renorm applied to match spectra at 1.5 keV Renorm applied to match spectra at 1.5 keV

pnpn

ACIS S3ACIS S3

ACIS S3 vs EPIC MOSACIS S3 vs EPIC MOSMOS2 appears to be more similar to ACIS in the MOS2 appears to be more similar to ACIS in the

0.7-1 keV band. 0.7-1 keV band.

MOS1 appears to be somewhere btwn. MOS2 MOS1 appears to be somewhere btwn. MOS2 and pn.and pn.

MOS2MOS2ACIS S3ACIS S3

Flux crossFlux cross-cal pn vs -cal pn vs ACISACIS

• Both figures have renorm factors: 5% for Both figures have renorm factors: 5% for the first; 15% for the second: let’s take the first; 15% for the second: let’s take them out.them out.

Flux crossFlux cross-cal pn vs ACIS-cal pn vs ACIS• Both figures have renorm factors: 5% for Both figures have renorm factors: 5% for

the first; 15% for the second: let’s take the first; 15% for the second: let’s take them out.them out.

Flux crossFlux cross-cal-cal

• The new HRMA calibration impacts on the The new HRMA calibration impacts on the ACIS/EPIC flux cross calibration.ACIS/EPIC flux cross calibration.

• Our analysis indicates that the flux cross Our analysis indicates that the flux cross calibration below calibration below ~ 2 keV ~ 2 keV will be shifted will be shifted by about 10%. by about 10%.

• Although comparing spectra extracted Although comparing spectra extracted from a given region of a cluster may not from a given region of a cluster may not be the best way to go, our data indicates be the best way to go, our data indicates that the flux cross calibration change is not that the flux cross calibration change is not for the better.for the better.

SummarySummary• The The newnew HRMA effective area reduces HRMA effective area reduces

ACIS S3 vs pn residual calibration errors ACIS S3 vs pn residual calibration errors to less than 5%to less than 5%

this is no small achievement!this is no small achievement!• Major remaining discrepancy in 0.7-1 Major remaining discrepancy in 0.7-1

keV bandkeV band• The new spectral calibration modifies by The new spectral calibration modifies by

about 10% Chandra fluxes below 2 keV, about 10% Chandra fluxes below 2 keV, ACIS vs EPIC flux cross calibration will ACIS vs EPIC flux cross calibration will be affectedbe affected