Experience with combined Experience with combined Fe55/Vela SNR calibration - MOSFe55/Vela SNR calibration - MOS

Andrea TiengoINAF, IASF-Milano

In collaboration with: Mariachiara Rossetti (IASF-Milano)

Martin Stuhlinger (ESAC)

Madrid, 23 March 2010

EPIC Calibration Meeting

A. Tiengo - Madrid, 23 March 2010

Observations on 2009-10-24/25:

3 observations of Vela SNR in the same orbit:

CALclosed: 40 ks

Thin: 40 ks

CALthin: 37 ks (after soft protons filtering)

A. Tiengo - Madrid, 23 March 2010

MOS2, CALthin:

0.2-10 keV 0.5-0.7 keV 5.7-6.1 keV

Pattern 0 spectra extracted from 4’ circle in CCD1

A. Tiengo - Madrid, 23 March 2010

MOS1, pattern 0, 4’ circle:

A. Tiengo - Madrid, 23 March 2010

MOS1, pattern 0, 4’ circle:

SNR lines Al line Mn line

ΔE = 0.4 1.2 eV ΔE = 1.7 0.9 eV ΔE = 5.1 0.9 eV

Shift to higher energies of Mn (and possibly Al) line and no shift for SNR lines same results as PN

A. Tiengo - Madrid, 23 March 2010

Possible explanation: optical loading?Since fixed offset maps are used, a wrong offset might

cause an incorrect energy reconstruction

A. Tiengo - Madrid, 23 March 2010

Possible explanation: optical loading?Background maps: offset maps reconstructed from energies

detected in peripheral pixels of each event

calthin – calclosed

(rawX,rawY)

At the position of bright stars, the optical loading is up to ~10 energy channels (~20 eV)

calthin – calclosed

(rawX,rawY)

A. Tiengo - Madrid, 23 March 2010

Possible explanation: optical loading?

Repeating the analysis excluding regions around the bright stars, the energy shifts

do NOT change

The shifts are NOT caused by optical loading

A. Tiengo - Madrid, 23 March 2010

Is it a CTI effect?Parallel CTI, MOS1 (analysis by Martin Stuhlinger)

Calclosed Calthin

A. Tiengo - Madrid, 23 March 2010

Is it a CTI effect?Parallel CTI, MOS1 (analysis by Martin Stuhlinger)

Calclosed Calthin

Generally, better CTI in calthin YES, it is a CTI effect

A. Tiengo - Madrid, 23 March 2010

Possible explanation: trap saturationIn CALthin observation, the high event rate (together with optical loading?) partially saturates traps less CTI, that is therefore overcorrected by SAS calibration lines are shifted at higher energies than in CALclosed observation

Readout

direction

Trap

Event 1

Event 2

Steve’s presentation in 2008

From analysis of bright AGNs: Possible rate-dependent gain shiftRemoving precursor events, shift is

unaffected not due to trap saturation?

However, pixel charge below event threshold may also partially fill the trap

Count rate BELOW each event is maybe a better indicator of TOTAL charge along readout direction

A. Tiengo - Madrid, 23 March 2010

Old NRCO: Tycho SNR

2008-01-01: CALmediumMOS1: 46 ks, MOS2: 36 ks

2008-01-03: CALclosedMOS1: 26 ks, MOS2: 26 ks

MOS2, Mn line shift:

SNR: +8.4 eVCCD1, no SNR: +4.1 eVCCD2-7: +0.1

[Vela pointing is too uniform to detect spatial variations of the energy shifts]

A. Tiengo - Madrid, 23 March 2010

Tycho, CALmedium, Mn lineRegions optimized to have ~ the same number of counts in Mn line (done by Mariachiara Rossetti)

From preliminary analysis, the line shift seems to correlate with count-rate BELOW (and not IN) extraction region, as expected for trap saturation (also by charge below threshold for event recognition).

MOS2 (rawX,rawY)MOS1 (rawX,rawY)

A. Tiengo - Madrid, 23 March 2010

Conclusions & future workCalibration source line centroids are shifted to higher energies when the sky is also observed, very likely due to trap saturation

• Does the effect disappear removing precursor events? If not, the traps may be filled by charge below threshold.

• Can this effect be calibrated? Further spatially-resolved analysis of Tycho and Vela SNRs and time-resolved analysis of SNRs or galaxy clusters (or calclosed?) with variable background