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Preliminary analysis of Long Term Trends in CZTI background

Preliminary analysis of Long Term Trends in CZTI background. Santosh Vadawale PRL, Ahmedabad. ACHEC Meeting, 12 th April 2016, TIFR. Astrosat - CZTI. Coded Mask imaging with pixilated CZT detectors. CZT modules. 4 x 4 cm 2 (16 x 16 pixel) 5 mm thick

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Preliminary analysis of Long Term Trends in CZTI background

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  1. Preliminary analysis of Long Term Trends in CZTI background Santosh Vadawale PRL, Ahmedabad ACHEC Meeting, 12th April 2016, TIFR

  2. Astrosat - CZTI Coded Mask imaging with pixilated CZT detectors CZT modules • 4 x 4 cm2 (16 x 16 pixel) • 5 mm thick • Total 64 modules (16 in 4 quadrants) • Total area 1024 cm2 • Total pixels 16384 • Pixel size 2.5 x 2.5 mm2 • Large detector plane with small pixel size • Prone to increased background due to simultaneous multiple events

  3. CZTI  Coded Mask Imager No need to worry about background!! • However, observed background was ~10 times higher!! • Impressive of cleaning data  systematic removal of events • ~90 % events rejected with ~1% time loss However • Cleaned background still 20 to 25 % higher then expected • Good background estimate needed for ‘non-mask weighted’ spectroscopy of bright sources • Accurate Compton background essential for polarization measurements

  4. CZTI background indicators • CZTI total event rate (Q) • CZTI ULD event rate (Q) • Veto count rate (Q) • CPM event rate • Temperature quadrant wise • Earth position of S/C (Lon., Lat.) • Pointing direction (RA, DEC) Investigating long term trends in CZTI background All data collected over most of the operational period (October 2015 to March 2016) Total number of observations > 200 some of them not yet fully processed (various reasons) Background data for total 137 observations

  5. Orbital variation

  6. Spatial Variation of Veto counts

  7. Veto – Long term variation

  8. CZT ULD – Long term variation

  9. CZT Total counts – Long term variation

  10. CZT Total Counts vs. Veto Counts

  11. CZT ULD CZT ULD CZT ULD CZT ULD CZT Total Counts vs. CZT ULD

  12. CZT ULD vs Veto Counts

  13. Preliminary Summary • Almost all rate are stable over long term • All rates vary over orbital period, as expected • Significant daily variation • Only weak correlation between CZTI counts and ULD / Veto • No correlation between CZTI counts and CPM or Quad Temperature • Stability / effect of module temperature to be investigated • No effect of S/C orientation on total CZTI counts, effect on Compton events to be investigated • Much more detailed analysis needed to investigate short term dependence on SAA (activation etc.) • Full modeling of background may not be essential for CZTI, but will be necessary for LAXPC

  14. Thanks…

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