1. ACHEC Meeting, 12th April 2016, TIFR
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 cm2
Total pixels
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 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…