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 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 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-X2JEM-X1 DV corrected gain Actual 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 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 22 keV compared to 9% just after launch The resolution of JEM-X2 is now about 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 HV-off about 5-10 min before internal JEM-X mechanism would have 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)