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Experience with combined Fe55/Vela SNR calibration - MOS

Madrid, 23 March 2010 EPIC Calibration Meeting. Experience with combined Fe55/Vela SNR calibration - MOS. Andrea Tiengo INAF, IASF-Milano In collaboration with: Mariachiara Rossetti (IASF-Milano) Martin Stuhlinger (ESAC). Observations on 2009-10-24/25:.

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Experience with combined Fe55/Vela SNR calibration - MOS

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  1. Madrid, 23 March 2010 EPIC Calibration Meeting Experience with combined Fe55/Vela SNR calibration - MOS Andrea Tiengo INAF, IASF-Milano In collaboration with:Mariachiara Rossetti(IASF-Milano) Martin Stuhlinger (ESAC)

  2. 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

  3. 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

  4. MOS1, pattern 0, 4’ circle: A. Tiengo - Madrid, 23 March 2010

  5. 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

  6. 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

  7. Possible explanation: optical loading? Background maps: offset maps reconstructed from energies detected in peripheral pixels of each event calthin – calclosed (rawX,rawY) calthin – calclosed (rawX,rawY) At the position of bright stars, the optical loading is up to ~10 energy channels (~20 eV) A. Tiengo - Madrid, 23 March 2010

  8. 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

  9. Is it a CTI effect? Calclosed Calthin Parallel CTI, MOS1 (analysis by Martin Stuhlinger) A. Tiengo - Madrid, 23 March 2010

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

  11. 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 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 Readout direction Event 1 Event 2 Trap Count rate BELOW each event is maybe a better indicator of TOTAL charge along readout direction A. Tiengo - Madrid, 23 March 2010

  12. Old NRCO: Tycho SNR [Vela pointing is too uniform to detect spatial variations of the energy shifts] 2008-01-01: CALmedium MOS1: 46 ks, MOS2: 36 ks 2008-01-03: 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 A. Tiengo - Madrid, 23 March 2010

  13. 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). MOS1 (rawX,rawY) MOS2 (rawX,rawY) A. Tiengo - Madrid, 23 March 2010

  14. 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 A. Tiengo - Madrid, 23 March 2010

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