Experience with combined Fe55/Vela SNR calibration - MOS Andrea Tiengo INAF, 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 /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: keV keV 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) CalclosedCalthin

A. Tiengo - Madrid, 23 March 2010 Is it a CTI effect? Parallel CTI, MOS1 (analysis by Martin Stuhlinger) CalclosedCalthin Generally, better CTI in calthin  YES, it is a CTI effect

A. Tiengo - Madrid, 23 March 2010 Possible explanation: trap saturation In 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 shift  Removing 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 : CALmedium MOS1: 46 ks, MOS2: 36 ks : CALclosed MOS1: 26 ks, MOS2: 26 ks MOS2, Mn line shift: SNR: +8.4 eV CCD1, no SNR: +4.1 eV CCD2-7: +0.1 [Vela pointing is too uniform to detect spatial variations of the energy shifts]

A. Tiengo - Madrid, 23 March 2010 Tycho, CALmedium, Mn line Regions 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 work Calibration 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