Evaluation of the EPIC flux cross-calibration

from 2XMM sources

R. Saxton, S. Mateos, A. Read,

S. Sembay

Mateos et al., 2009, A&A, arXiv.0901.4026

2XMM sources

pn vs MOS1 energy dependence

MOS1 vs MOS2 energy dependence

Distributions of flux ratios fitted with Gaussian profiles:

pn vs MOS1:energy dependence

pn / MOS agreement worse above ~4.5 keV (12.5%)

~constant offset from MOS cameras of 7-9% from 0.5-4.5 keV

pn / MOS agreement better than

3% in 0.2-0.5 keV band 1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

MOS1 vs MOS2:energy dependence

MOS cameras agree to better than 4% at all energies

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

pn vs MOS1:offaxis dependence

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Variations of MOS vs pn relative flux calibration vs offaxisARF effect: QE: spatial variation in QE offaxis (MOS and pn) Vignetting: General vignetting function PSF: Uncertainties in offaxis PSF

1

2

3

4 1

2

3

4

Azimuthal dependence - PN v MOS-2

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Strong azimuthal-angle dependence at high energies

1

2

3

4 1

2

3

4

RGA obscuration: Azimuthal dependenceExcluded sources at offaxis<2 arcmin

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Sources divided in 4 azimuthal angle binsbased on DETX/DETY coordinates

Strong azimuthal angle dependence at high energies Sources lying along the RGA dispersion axis show a large

gradient in relative flux Calibration of RGA blocking factor incorrect at high energies?

B-4 B-4

B-4 B-4 B-4

B-5 B-5

1

2

3

4 1

2

3

4

RGA obscuration: Azimuthal depencence

Strong azimuthal angle dependence at high energiesSources lying along the RGA dispersion axis show a large

gradient in relative flux

Calibration of RGA blocking factor incorrect at high energies?

Excluded sources at offaxis <2 arcmin

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Sources divided in 4 azimuthal angle binsbased on DETX/DETY coordinates

B-5

B-4 B-4B-4

B-5 B-4

B-5

Current azimuthal vignetting factor for MOS-1

1.5 keV@ 9 amin offax

9 keV@ 9 amin offax

1

2

3

4 1

2

3

4

Low-energy azimuthal dependence: MOS-1

Strong azimuthal angle dependence at low energiesSources lying on CCDs from different batches show a large

gradient in relative flux

Excluded sources at offaxis< 2arcmin

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Sources divided in 4 azimuthal angle binsbased on DETX/DETY coordinates

B-5

B-4 B-4B-4

B-5 B-4

B-5

1

2

3

4 1

2

3

4

Excluded sources at offaxis<2 arcmin

1:0.2-0.5 keV2:0.5-1 keV3:1-2 keV4:2-4.5 keV5:4.5-12 keV

Sources divided in 4 azimuthal angle binsbased on DETX/DETY coordinates

Smallish azimuthal angle dependence at low energies.Batch effect not so strong here ?

B-4 B-4

B-4 B-4 B-4

B-5 B-5

Low-energy azimuthal dependence: MOS-2

Consistent improvements in the MOS2/pn flux ratio, with some evidence for similar improvements for MOS1/pn

Large scatter, low stats at very lowest energy so far

Conclusions• Excellent agreement of the two MOS cameras (<4%) at all energies

• MOS cameras register 7-9% higher flux than pn below 4.5 keV10-13% flux excess at the highest energies

• No evolution of flux ratios with time except in the 0.2-0.5 keV bandGradual degrading of the MOS redistribution function

• MOS to pn excess increases with offaxis: ARF effect

• Strong dependency of MOS to pn excess 4.5-12 keV flux on azimuthal-angle

TO DO• Fudge RGA obscuration to give larger azimuthal effect for MOS’s

at high energies ? Use SCISIM to justify physical parameters ?

• Put in a batch-specific, low-energy QE contribution for MOS-CCDs ?

• 2XMM could benefit from: - MOS RMFs made spatially, temporally dependent. - EBG PSF ? - Spectral dependence in flux calculation

• Strong dependency of MOS to pn excess 4.5-12 keV flux on azimuthal-angle Calibration of RGA blocking factor (RGA absorption) incorrect at high energies?