Origin of gain offsets: new insights from eROSITA calibration

1. Origin of gain offsets: new insights from eROSITA calibration EPIC Calibration & Operations Meeting Mallorca, Spain, 2008 April 7 - 8

2. Gain/temperature correlation: earlier investigations

3. Mn-Kα position vs. temperature: CCD 3 & 4

4. Deviations of the Al-K and Mn-Kα positions

5. Mn-Kα position vs. Al-K position

6. “CCD offsets”

7. Spektr-Rentgen-Gamma (SRG) Спектр-рентген-гамма to be launched in 2011 from Baikonur into 600 km / 30° orbit with Soyuz-Fregat eROSITA (D) Calorimeter (NL,US,J) ART-XC (Ru) LWFT (UK) "LOBSTER" Spacecraft "Navigator" (Ru)

8. eROSITA

10. eROSITA / TRoPIC calibration adu Energy [keV] Energy [keV] x = 0 .. 127 x = 128 .. 255

11. peak position: deviation from nominal value [adu] Energy [keV] Energy [keV] x = 0 .. 127 x = 128 .. 255 eROSITA / TRoPIC calibration

12. Deviations of the Al-K and Mn-Kα positions

13. eROSITA / TRoPIC calibration simulation peak position: deviation from nominal value [adu] Energy [keV] Energy [keV] “charge loss” independent of energy - 25 adu - 35 adu

14. eROSITA / TRoPIC calibration simulation peak position: deviation from nominal value [adu] Energy [keV] Energy [keV] “charge loss” dependent on energy - 25 adu · exp(-E/keV) - 35 adu · exp(-E/keV)

15. “Gain offsets” are observed at EPIC pn and eROSITA Due to the enhanced spectral capabilities towards lower energies, they can be better studied with eROSITA ..

16. eROSITA / TRoPIC input: 6 long flatfield exposures at B-K, C-K, Cu-L, Al-K, Cr-K, Cu-K selection of all singles in the 20 CCD rows closest to the CAMEX no corrections applied peak positions determined separately for CAMEX-1 and CAMEX-2

19. offset: ~ - 18 adu @ 0 eV 0 adu @ ~ 14 eV

23. eROSITA / TRoPIC Application of the cti and gain correction derived for singles

24. HK071119.007 Al-K monochromator (1.486 keV), NLL=0A00 (10s), SPLT=0028 (40a)

25. Cu-K (8.040 keV) high threshold (~130 adu)  overcorrection of doubles not due to noise collection

26. Cr-K (5.410 keV)

27. Cr-K B-K Cu-K Al-K

28. eROSITA/TRoPIC Gain Correction • Patterns cannot be corrected by any gain(E) function which is applied to their components individually, even if this function is made dependend on (x,y) and the pattern type.  If correction for singles is applied, then patterns become overcorrected, with the amount of overcorrection monotonically increasing with pattern size What is the reason ? • why offset ? • why overcorrection for patterns ?

29. eROSITA/TRoPIC Gain Correction • why offset ? • why overcorrection for patterns ? • nonlinear amplification ? • offset calculation ? • common mode ? • pileup with noise ? • frame store ? • partial events ?

30. E = 6.0 keV 0.1 keV 5.9 keV E = 0.1 keV E = 5.9 keV Charge Loss due to Partial Events E = 0.1 keV E < 0.1 keV

31. eROSITA/TRoPIC Gain Correction • why offset ? • why overcorrection for patterns ? • nonlinear amplification ? • offset calculation ? • common mode ? • pileup with noise ? • frame store ? • partial events ? • threshold !

32. Low Energy Threshold General consequences data corrected with gain derived from singles data set: HK070705.011 Macor, 15 kV, 4.2 V, EPIC-Filter, 5 Sigma, 20 adu 6.1 million events

34. Low Energy Threshold Dependence of the peak position derived from singles on the low energy threshold data corrected with gain derived from singles data set: HK070705.011 Macor, 15 kV, 4.2 V, EPIC-Filter, 5 Sigma, 20 adu 6.1 million events

35. 20 adu 80 adu 140 adu 30 adu 90 adu 150 adu 40 adu 100 adu 160 adu 50 adu 110 adu 170 adu 60 adu 120 adu 180 adu 70 adu 130 adu 190 adu

36. HK070705.011

37. Threshold Induced Charge Loss threshold zero level

38. Threshold Induced Charge Loss threshold zero level

39. eROSITA/TRoPIC Gain Correction offset: ~ - 18 adu @ 0 eV 0 adu @ ~ 14 eV

40. peak position: deviation from nominal value [adu] Energy [keV] Energy [keV] x = 0 .. 127 x = 128 .. 255 eROSITA / TRoPIC calibration

41. XMM-Newton / EPIC pn deviations of the Al-K and Mn-Kα positions

42. Triple: 8 borders 3 singles: 12 borders  border filling factor: 8/12 Single: 4 borders Double: 6 borders 2 singles: 8 borders  border filling factor: 6/8 Quadruple: 8 borders 4 singles: 16 borders  border filling factor: 8/16 Patterns, Borders, and Threshold Induced Charge Loss

43. Double: 6 borders but: correction for 8 borders  overcorrection: -6/8 + 8/8 = +2/8 = +0.25 Triple: 8 borders but: correction for 12 borders  overcorrection: -8/12 + 12/12 = +4/12 = +0.33 Quadruple: 8 borders but: correction for 16 borders  overcorrection: -8/16 + 16/16 = +8/16 = +0.50 Patterns, Borders, and Threshold Induced Charge Loss Single: 4 borders correction for 4 borders   predicted overcorrections: d : t : q = 3 : 4 : 6

44. Cu-K: doubles: +67 eV triples: +95 eV quadruples: +157 eV measured: d : t : q = 2.6 : 3.6 : 6.0 predicted: d : t : q = 3 : 4 : 6 ratios somewhat different for lower energies: partial event effect ?

45. “cutoff” gain “cutoff” gain + “electronic” gain eROSITA / TRoPIC calibration nonlinear “electronic” gain

46. eROSITA/TRoPIC Gain Correction • Implications for the gain correction algorithm for pn CCDs: • apply first the “electronic” gain correction to all events (i.e., singles and pattern components) • recombine the events to photons • apply then the “cutoff” gain correction (depending on energy and pattern size) to all photons in order to recover the lost charge and to linearize/adjust the energy scale  first results:

47. B-K (0.183 keV) Macor singles 0.187 keV doubles 0.189 keV triples 0.190 keV quadruples 0.186 keV

48. Al-K (1.486 keV) Cu-K (8.040 keV) singles singles 1.481 keV 8.034 keV doubles doubles 1.485 keV 8.032 keV triples triples 1.489 keV 8.037 keV quadruples quadruples 1.485 keV 8.033 keV

49. The situation for EPIC pn While there is clear evidence for an offset in the gain, there is no overcorrection of the energy for patterns observed

50. EPIC pn