JEM-X Status

S. Brandt on behalf of the JEM-X team

Partly based on a presentation at ESOC, Feb 2005 at review

marking the end of the nominal INTEGRAL mission

ESAC, March 14, 2005

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 2

Hardware performance (no news)

• Electronics– The performance of the JEM-X electronics has been nominal

– No resets of DFEE CPU

– No ageing of FPGA

– Unchanged performance of amplifiers

• Mechanical– No gas leak of Be window

– No detectable contamination of the Xe gas

– Detector collimator geometrical details are harder to model than expected. Vignetting function at large off-axis angles has some uncertainties.

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 3

Software performance

• DFEE software– Performance has been nominal

– Software patches have been introduced to tune detector performance and increase event processing speed (no new ones recently)

• DPE software– Performance of IASW and CSSW have been nominal

– One SW patch to correct broadcast packet interpretation

– SW patch to raise class of OEM 191 is pending

– One reset of CSSW/IASW has occurred; most likely due to SEU

– A few cases of failure to restore context after DFEE switch-off has occurred (one recent case during December eclipse season was quickly corrected by MOC)

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 4

Detector performance (is stable and unchanged)• Anomaly I

– Degradation (loss of anode strips) of detector micro-strip due to heavy cosmic ray nuclei– Action:

• Reduce HV from 900V to 820V, reducing the gain from ~1500 to ~600

• Use only one JEM-X unit at a time for the nominal mission

– Impact:• Lower sensitivity in the ~3 to ~4 keV range

• One unit only provides lower sensitivity for weak sources

• Anomaly II– Steady increase of detector gain over time due to ion drift in glass substrate– Action:

• Reduce HV one step (10 V) when needed to maintain constant gain within +- 10%

– Impact:• Slowly degrading energy resolution

• Slow change of spatial gain map

• Operational inconvenience

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 5

Status of the microstrip anodes Six anodes have been lost since JEM-X1 was reactivated in March 2004. We do not expect a similar loss rate in the future since three of these anodes were in a weak group already in Nov.-Dec. 2002.

JEM-X1 February 2003 JEM-X1 March 2004 JEM-X1 January 2005

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 6

JEM-X detector gain increase (ageing) • Both units show increase of gain of ~1% per orbit of use (HV on) relative to

the original gain relative gain increase slows down to ½% per orbit after 100 orbits and to 1/3% after 200 orbits of use

• Slow-down of gain increase in JEM-X1 due to lower temperature is inconclusive, but average lowering of detector tempeture is only ~2.5C

• Lower temperature may slow down degradation of energy resolution

JEM-X2 JEM-X1

DV corrected gainActual gain

DV corrected

gain

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 7

Temporary gain recovery

• After extended period of HV-off the gain returns to its original value (the charge configuration is restored)

• However, accelerated ”ageing” to a stable state then occurs over a period of 10-20 hours

• Activation of dormant unit for science use should take this effect into account

• Also impact on data taken after extended period of solar activity (like Jan 2005, where HV was off for 1 week)

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 8

Detector resolution evolution• The energy resolution is slowly

degrading (slower in JEM-X1 than in JEM-X2)

• The resolution of JEM-X1 is now 10.5% @ 22 keV compared to 9% just after launch

• The resolution of JEM-X2 is now about 12% @ 22 keV

• The gain evolution may be slightly non-uniform over the plate, causing a slow drift in the spatial gain map

• The spatial gain map is monitored by the Xe flourecense background line at 30 keV

JEM-X1

JEM-X2

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 9

JEM-X HV setting

• Due to ”frequent” lowering of the HV setting to keep a constant gain the HV value is now set by ISOC

• However, a conservative HV setting must be kept in the MOC DB to avoid high gain after manual recovery

• Responsibility of the instrument team to plan ahead and coordinate with MOC DB updates Example of JEM-X gain after recovery

performed where the MOC DB contained ”old” HV setting

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 10

JEM-X IREM Reaction is disabled• Experience shows that JEM-X internal radiation protection logic works well

• Software switch-off mechanism only active when in data taking (but that is almost always the case)

• Hardware switch-off mechanism always active

• Using IREM may cause loss of science time

• Conclusion: disable JEM-X reaction to IREM (OCR #183 implemented)

Example of ”normal” IREM induced Example of ”normal” IREM induced HV-off about 5-10 min before internal HV-off about 5-10 min before internal JEM-X mechanism would have JEM-X mechanism would have triggered. triggered.

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 11

Correlation of the JEM-X background rate and ground based cosmic ray monitor data from Oulu

•The JEM-X noise count rate has grown by 40 % since the start of the mission.

•The increase is closely correlated with the cosmic ray activity as measured by ground based neutron monitors.

JEM-X

Oulu

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 12

Expected evolution of the background

Oulu 40 years cosmic ray history

JEM-X/INTEGRAL 2 years

The prediction is that the JEM-X rate will increase by another 20-40% as the Solar minimum evolves

What about IBIS and SPI ?

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 13

Dither pattern

• HEX dither is preferred when continuous JEM-X coverage is important

• 5x5 dither does not provide continuous coverage and vignetting far off-axis is still not completely modeled

• Staring observations introduce artifacts in the imaging and is discouraged

• Artifacts in HEX and 5x5 observations may be further reduced by not exactly repeating the pointing pattern (suggested scheme from Niels Lund)

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 14

Moving the center point for hex dithers

40’

72’

120’

Original dither points

Additional center point positions

Original center point

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 15

Sensitivity gain by operating both JEM-X units:improvement for (isolated) weak sources

•Assumptions: 100 counts per TM packet, 30 c/s background per unit, 1 Crab is 125 c/s, 7 science TM packets per 8 sec

• 2 gain below ~110 mCrab total source flux, no gain above 460 mCrab

•For allocation of 10 science TM packets, 2 gain below ~260 mCrab, no gain above 760 mCrab

•General improvement of imaging by reduction of artifacts

•Detector ageing increases by a factor of 2

10 science TM

7 science TM

SDAST Meeting, March 2005 JEM-X Status Søren Brandt page 16

Conclusions• The JEM-X performance has been nominal, aside from the ”ageing” of the micro-

strip substrate described above• Operations have been smooth, with efficient and competent monitoring and

speedy recovery actions at MOC, keeping the loss of observing time to an absolute minimum

• The planning at ISOC has been efficient and the support for the Observers Manual has been strong

• The monitoring of the science TM by the ISDC operators has been helpful and the extra support for the JEM-X Instruments Station has been much appreciated

• The handling of ”change requests” has been very flexible and great efforts have been put into finding ways of implementing the wishes of the JEM-X team

• The Coordination Meeting has been an important forum for the Instrument Team to gain understanding of the different branches of the ground segment

• JEM-X is ready to support the continued operations of INTEGRAL• Lesson learnt: Instrument team access to raw data should have been should

have been included in the system design

NOT THE END of INTEGRAL (or JEM-X)