Gain Offset evolution on IBIS
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Gain Offset evolution on IBIS
03/05/2016
1
Réunion ECLAIRs science
IBIS/ISGRI energy calibration
03/05/2016
2
Réunion ECLAIRs science
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
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% !
3
IBIS/ISGRI energy calibration details (1)
03/05/2016
4
Réunion ECLAIRs science
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
g
0
and offset
a
0
,
pha
1
=
a
0
+g
0
* PHA
2/ time drift correction: E
estimate
= 2* (pha
1
– a
1
) / g
1
3/ correction of charge loss:
index (calculated from
E
estimate
and
RT with a random part) in a LUT2 table gives real energy.
pha
1
< specific energy
(around 50 keV @revol 0650, RT=25):
a
1
= o
PH1
= -5.655 ±0.001
and
g
1
= g
PH1
+ a
PH1
*revol
IBIS/ISGRI energy calibration details (2)
03/05/2016
5
Réunion ECLAIRs science
pha
1
< specific energy
(around 50 keV @revol 0650, RT=25):
•
a
1
= o
PH1
= -5.655 ±0.001 [ch]
•
g
1
= g
PH1
+ a
PH1
*revol
with g
PH1
=2.047 ±0.001 [ch/keV] and
a
PH1
= (-6.1 ±0.1) 10
-4
[ch/keV/revol]
with 122 revol/year,
g
1
decreases of 3.6% per year
Figure on right:
g
1
evolution for
several RT intervals (law1 is with
the constant offset
o
PH1
).
g
1
E
lim
+ a
1
= Cte, whatever law
pha
1
> specific energy (E
lim
):
•
a
1
= o
PH2
(RT) + c(RT)*revol + d(RT)*revol²
•
g
1
= g
PH2
(RT) + b(RT)*revol
IBIS/ISGRI energy calibration LT
03/05/2016
6
Réunion ECLAIRs science
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:
LT in keV
with drift (law1,
no RT dependance).
This content explores the evolution and drift in the gain and offset calibration of IBIS/ISGRI energy measurements onboard the INTEGRAL satellite. It discusses the challenges faced, such as sudden drifts during solar flares, and the methods used to calculate gain and offset values over time. Detailed information is provided on the measurement techniques, corrections applied, and the impact of solar flares on calibration stability. The content delves into specific cases, such as the significant solar flare of 2003 and the adjustments made to maintain accurate energy calibration. Various image objects are included to visually represent the concepts discussed.
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Presentation Transcript
Gain Offset evolution on IBIS A. Sauvageon CEA/IRFU/SAp R union ECLAIRs science 1 03/05/2016
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. R union ECLAIRs science 2 03/05/2016
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% ! Gain and offset (0040 to 0185, corrected from Temperature) OFFSET GAIN 0.30 1.005 0.15 1.003 0.00 1.000 -0.15 0.998 -0.30 0.995 -0.45 0.993 -0.60 0.990 -0.75 0.988 -0.90 0.985 REV44 49 54 59 64 69 74 79 84 89 94 99 104109114119124131136141146151156161166171176181 R union ECLAIRs science 3 03/05/2016
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 g0and offset a0, pha1= a0+g0* PHA 2/ time drift correction: Eestimate= 2* (pha1 a1) / g1 3/ correction of charge loss: index (calculated from Eestimateand RT with a random part) in a LUT2 table gives real energy. pha1< specific energy (around 50 keV @revol 0650, RT=25): a1= oPH1= -5.655 0.001 and g1= gPH1+ aPH1*revol R union ECLAIRs science 4 03/05/2016
IBIS/ISGRI energy calibration details (2) pha1< specific energy (around 50 keV @revol 0650, RT=25): a1= oPH1= -5.655 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, g1decreases of 3.6% per year Figure on right: g1evolution 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)*revol g1= gPH2(RT) + b(RT)*revol R union ECLAIRs science 5 03/05/2016
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: LT in keV with drift (law1, no RT dependance). R union ECLAIRs science 6 03/05/2016
