1. A. Sauvageon CEA/IRFU/SAp
Gain Offset evolution on IBIS
A. Sauvageon CEA/IRFU/SAp
03/05/2016
Réunion ECLAIRs science

2. IBIS/ISGRI energy calibration
All information come from doc:
« INTEGRAL IBIS/ISGRI energy calibration OSA 10 »
OSA = Off-line Standard Analysis.
The ISGRI spectral gain has been observed to decrease with time.
Initially (OSA 5) this drift was set proportional with time (in fact the revolution number, around 122 orbits per year).
But it did not account for sudden drifts due to solar flares (see next page). So, an attempt (OSA 7) was made to calculate gain and offset as functions of cumulative counters of IREM instrument on INTEGRAL (total dose, proton, ions and electron in various energy bands). But these counters had problems.
Finally, it was set again (OSA 10) proportional to revolution, but keeping from OSA 7 the 2 cases: below and above 50 keV.
03/05/2016
Réunion ECLAIRs science

3. Drift during huge solar flare
This flare occurred in orbits 0126 to 0129 (from 26/10/2003 to 05/11/2003, rated at least X28, more than twice as large as any previously recorded flare).
Normally, the gain decrease is around 3.6% per year, i.e. 0.1% for 10 days. This drift during this 10 days flare was 0.7% !
03/05/2016
Réunion ECLAIRs science

4. IBIS/ISGRI energy calibration details (1)
What is measured:
Pulse Height Amplitude (PHA, a channel) and Rise-Time (RT, time for the pulse to reach its maximum, i.e. interaction depth in 2 mm CdTe).
Energy correction is made in 3 steps:
1/ normalization between pixels, and for temperature/voltage (pixels coef. in a table called LUT1 and fixed laws)
gain g0 and offset a0, pha1 = a0+g0* PHA
2/ time drift correction: Eestimate = 2* (pha1 – a1) / g1
3/ correction of charge loss: index (calculated from Eestimate and RT with a random part) in a LUT2 table gives real energy.
pha1 < specific energy (around , RT=25):
a1 = oPH1 = ±0.001 and g1 = gPH1 + aPH1*revol
03/05/2016
Réunion ECLAIRs science

5. IBIS/ISGRI energy calibration details (2)
pha1 < specific energy (around , RT=25):
a1 = oPH1 = ±0.001 [ch]
g1 = gPH1 + aPH1*revol with gPH1=2.047 ±0.001 [ch/keV] and aPH1= (-6.1 ±0.1) 10-4 [ch/keV/revol]
with 122 revol/year, g1 decreases of 3.6% per year
Figure on right: g1 evolution for
several RT intervals (law1 is with
the constant offset oPH1).
g1 Elim + a1 = Cte, whatever law
pha1 > specific energy (Elim):
a1 = oPH2(RT) + c(RT)*revol + d(RT)*revol²
g1 = gPH2(RT) + b(RT)*revol
03/05/2016
Réunion ECLAIRs science

6. IBIS/ISGRI energy calibration LT
Low Threshold (LT) is set with a command value between 0 and 63 (63 for dead pixels).
LT function corresponds
to a Heaviside function
convoluted to a Gaussian function.
Black line:
LT in keV
(no drift)
Red line:
with drift (law1,
no RT dependance).
03/05/2016
Réunion ECLAIRs science