The International Gamma-RayAstrophysics Laboratory- 1 Year in Orbit

Contact: ESA Publications Divisionc/o ESTEC, PO Box 299, 2200 AG Noordwijk, The NetherlandsTel (31) 71 565 3400 - Fax (31) 71 565 5433Visit ESA Publications at: http://www.esa.int

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BR-210November 2003

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Contributors:Kai ClausenPhlippe SivacEliseo BalaguerGiuseppe SarriArvind ParmarMichael SchmidtLars HanssonRudolf MuchPaolo Strada

Published by:ESA Publications DivisionESTEC, PO Box 2992200 AG NoordwijkThe Netherlands

Editor: Bruce BattrickDesign & Layout: Carel Haakman

Price: 10 EurosISSN: 0250-1589ISBN: 92-9092-667-8Printed in: The Netherlands© ESA 2003

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Contents2 Introduction

4 Launch Campaign

12 Space Operations

14 Science Operations

16 Science Highlights

20 Second Announcement of Opportunity and Future Plans

IntegralThe International Gamma-RayAstrophysics Laboratory- 1 Year in Orbit

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The Integral project began more than 10 years ago, in July 1993,with the aim of providing a full-size high-energy observatorywithin a medium sized budget. ESA actually used less than themedium sized budget, but it certainly required a great deal ofenergy to get there. The project had to struggle with a series ofchallenges: the spacecraft bus was to be shared with the XMM-Newton mission, but to be procured and integrated by a differentprime contractor, Alenia. This worked remarkably well. Thelauncher Proton was to be provided by Russia in return forobserving time, but the political, social and economic turmoilduring the changeover from the Soviet Union to the RussianFederation meant that it took many long and agonizing years toturn the intention first into commitment and then reality. Butfinally we got a wonderful launch and Russia is getting wonderfulscientific data in return.

The biggest challenge, however, was the payload. Just after thestart of the Integral Project, NASA, which was supposed toprovide the spectrometer, pulled out due to alternative prioritiesand the United Kingdom, supposed to provide the imager andoptical monitor, pulled out due to lack of funds. Never wasIntegral closer to cancellation, and so soon after its inception.

However, in a truly European spirit, brave volunteers stood upto take over. A Franco-German team took on the spectrometer, anItalian-French team the imager, and a Spanish team the opticalmonitor. How brave they really were soon became evident. Thedevelopment of these observatory-type instruments with littletechnology heritage proved to be a formidable challenge. Theproject team had to get more deeply involved and had to providemuch more support than foreseen. The launch date had to bepostponed three times due to payload problems! Again, finallywe got there.

In view of these challenges and looking back over all the busy,exciting and exhausting years of our lives dedicated to Integral,we are even more satisfied and happy to have achieved a perfectlaunch and a smooth commissioning in orbit, and then to havewitnessed a year of flawless spacecraft operations and promisingscientific observations.

Introduction

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1 Year In Orbit

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Launch CampaignThe launch campaign lasted less than

two months - a rather short time frame for a large, one-of-a-kind satellite likeIntegral. The campaign began in earneston 25 August 2002 with the arrival of thetwo satellite modules at the BaikonurCosmodrome in Kazakhstan. Afterreassembly, final electrical verifications,link checks with ESA’s European SpaceOperations Centre (ESOC) in Darmstadt(D), and fuelling, Integral was ready formating with the Proton launcher. On 12October, five days before the scheduledlaunch, the complete launch vehicle, withIntegral safely under the upper-stagefairing, was rolled out of the assembly hallat precisely 06:30 local time. By 11:00, thelauncher, now clamped in a verticalposition, was ready for the final five daysof preparation and ground checks.

October 17 - Launch Day

It was a cold start to the day in Baikonur,with early-morning temperatures ofaround –7°C, as the ESA and Russianteams made their way to their respectivework areas for the final countdown. Sixhours before launch, the job of fuellingthe first three stages of the Protonlauncher with more than 600 tons ofpropellant began. Three hours later, theprocess was complete. Despite stronghigh-altitude winds, in excess of 100 km/hat 11 km altitude, which were close to thelimit of acceptable launch conditions, thego-ahead was given to power-up Integral.About 1 hour before lift-off, the relevantauthorities confirmed the launch andgave permission to pull back the servicetower. Integral, now powered by its ownbatteries, was switched into launchconfiguration by ground controllers.Ten minutes before lift-off, the spacecraftand ground segment confirmed theirreadiness for launch to the launchauthorities. At 04:41 UT, right on schedule,the Proton rocket powered off the launchpad and into the sky.

The launch of Integral from Baikonur on 17 October 2002

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Date Time Event25-08-2002 Arrival of Integral at Baikonur12-10-2002 Integral rollout16-10-2002 22:41:00 Start propellant loading of Proton rocket17-10-2002 1:49:00 Integral spacecraft powered up

3:23:00 Start service tower rollback3:36:00 Start of check-out of US3:55:00 Completion service tower rollback3:56:00 Start of check-out of LV4:11:00 Integral declared ready for launch4:36:00 LV declared ready to launch4:39:00 US is initialised and changed to internal power4:39:07 US declared ready for launch4:40:58 Lift-off command - launch irreversible4:41:00 LIFT OFF4:50:50 Separation of orbital modules (US and Integral)

- Injection into parking orbit5:01:00 End of radio contact5:41:37 Radio signal acquired in Argentina5:43:22 Start of US Main Engine burn5:50:27 End of US Main Engine burn5:53:12 End of radio signal over Argentina6:01:30 Radio contact with Vilspa6:04:22 Radio contact with Redu6:10:10 Radio contact with US and Russian ground stations6:13:26 Integral separation from US6:27:26 Deployment of 1st solar panel6:31:26 Deployment of 2nd solar panel8:08:26 Swith on of star tracker A16:00:00 Switch on and activate IREM18:22:00 Start of SPI Activation22:32:00 Start of JEM-X 1 activation

18-10-2002 0:30:00 Start of JEM-X 2 activation18:35:00 Start of IBIS activation

19-10-2002 6:00:00 Start of OMC activation20-10-2002 0:00:55 Perigee passage - end of orbit 124-10-2002 6:00:00 Start of first orbit manoeuvre (PRM)31-10-2002 9:54:53 Start of final orbit manoeurve (AAM)03-11-2002 JEM-X Detection of Cyg X-305-11-2002 1st SPI gamma-ray image14-11-2002 JEM-X Detection of LMC X-3 and LMC X-417-11-2002 IBIS, SPI and JEM-X detection of Cyg X-125-11-2002 1st GRB imaged by IBIS18-12-2002 Integral first light19-12-2002 1st GRB detected by IBAS in IBIS field of view30-12-2002 End of PV phase29-01-2003 ISGRI detection of 1st transient source31-01-2003 GRB, 100 s duration, imaged by IBIS27-02-2003 1st SPI image and spectrum of GRB03022720-03-2003 GRB030320 - 5th GRB16-05-2003 Data distribution to guest observers15-07-2003 2nd Announcement of Opportunity11-08-2003 Integral completes 100 orbits17-10-2003 Integral celebrates 1 year in orbit

Launch Campaign, Early Operations and Mission Milestones

Proton Rocket Launch Profile

The First Phase of the Flight

Just ten minutes later and the first threestages of the launcher had boosted thefourth, or upper, stage into a 192 by 690km parking orbit.This first success was asource of great satisfaction for theteams watching around the world.Subsequent analysis of the Proton flightenvironment indicates that the flightloads were much lower than predicted.The maximum accelerations, equivalentsine levels and acoustic loads were allwell within the qualification levelsapplied during spacecraft testing.

The fourth stage and Integral were nowheading south, over the SouthernPacific, before heading back north, overSouth America for the fourth-stageburn and satellite separation.

Final Orbit Insertion

The fourth stage of the Proton launcherboosted Integral into a highly eccentricorbit.The Russian company Energia wasboth the supplier of this stage (Block-DM) and in charge of the tracking andcontrol operations. The firing of theBlock-DM was to take place overArgentina and was essential to thesuccess of the mission. Energia did notpossess any tracking capabilities inSouth America, so they approached theIntegral Project Team for support in theplacement of a mobile station capableof tracking the fourth stage’s firing andorbit injection.

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After an intensive effort at the technical,logistical and human level (including avisit by ESA’s Director General toArgentina) between the Integral ProjectTeam, CONAE (the Space Agency ofArgentina) and Energia, the mobilestations were on their way by ship toBuenos Aires. The Argentineans were,from the outset, extremely friendly andhelpful, and so the potentially dauntingimportation and customs formalitieswere quickly dealt with.

"Being the only Spanish speaking memberof the Project Team I volunteered to supportthe mobile station campaign in Argentina.Of course, I was sad to leave the launchcampaign activities in Baikonur, but it wasa pleasure to liaise with the Argentineanspace authorities."Eliseo Balaguer

Soon the convoy was speeding along thehighway to Mar del Plata with twoRussian vans, a team of six Russians, twoArgentinean drivers, an interpreter and aCONAE representative. Part way throughthe journey we had a brief moment ofpanic when the police stopped theRussian vans - but it was only to ask themto deliver official documentation to thenext police station!

Our destination was a fishing researchinstitute conveniently located in the portregion of Mar del Plata with a good viewof the Integral orbit.The Russian team didan excellent job in installing the stationsin a very short time. In fact the job wasdone so quickly that the next day therewas a ‘technical first’ in the SouthernHemisphere: the cosmonauts aboard theInternational Space Station switched on aSoyuz transponder as the Station passedover Argentina so that we could validatethe mobile stations.

The only disturbing incident beforeIntegral’s launch was a torrential stormand subsequent flood that transformedthe mobile station site into a swimmingpool, forcing us to improvise scaffoldingfor the station cabling with ladders andother materials.

In Mar del Plata it was almost quarter totwo in the morning when Integral waslaunched. The night was, for the first timein a while, very cold and clear. It was a joyone hour later to see the satellite’s rocketengine firing, not only from the telemetryreadout on the screens, but alsophysically in the sky, clearly movingtowards its new orbit.

The media coverage in Argentina wasimpressive with front-page features inlocal and national papers and a smallstory on Integral on prime-time TV, whichfilmed the operations of the mobilestation. It was an exciting experience towitness the launch in this way and all themembers of the team remember thefriendly and warm support from Argentina.

Spacecraft Commissioning

For most launch-team members, thetremendous anxiety that accompaniesany launch evaporates at lift-off intoscenes of jubilation. But for those whohave specific post-launch tasks, both at

One of the mobile support stations installed at Mar del Plata inArgentina

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the Launch Site and obviously at theControl Centre, the realisation that rocketand spacecraft have left home for goodblends with the awareness that the roadahead is long and treacherous and thereal excitement is yet to begin. An intensebut contained satisfaction thereforepermeates the entire Control Centre.

Sitting in the Main Control Room at ESOC,a brief scan around the room wouldreveal a crowd of familiar faces,concentrating hard, and glued to theirmonitors; both newcomers at their firstlaunch and seasoned engineers, allexperiencing the full spectrum ofemotions as events began to unfold.Years of study, diligent effort andintensive training would be finallybrought to bear, starting from themoment of ‘separation’. From this eventon, the success of the Integral missionwould literally depend on their timelines,procedures, brains and fingertips.

The operations teams at ESOC had beenin contact with the launch sitethroughout the countdown phase,monitoring the status and health of the

onboard systems until just before lift off.The first telemetry contact wasestablished from the Spanish groundstation in Villafranca, the announcementflashed through the intercom to allpositions. We were still 10 minutes fromseparation when the ESA ground stationat Redu (Belgium) confirmed, 3 minutesafter the first contact, that Integral was ontrack and performing well.

"I lay back on my seat, savouring for a splitsecond the privilege of being part of theextraordinary organisation of teams andtechnology that makes such a space missionpossible. Even after many simulations, evenfor toughened engineers, the thrill of thereal thing is irresistible. So irresistible thatthe second shift team is also slowlygathering around the workstations; theywill rest after separation and after the arraydeployment, of course; who could sleepanyway?"Paolo Strada

Exactly 1hour 32minutes and 26secondsafter lift-off, as planned, the spacecraftseparated from the Proton upper stageand the automatic activation of theonboard systems took place flawlessly.

The familiar separation sequence,rehearsed during so many simulations,was now executing for the last time, forreal. Gradually, almost magically, four tonsof satellite sprang into life, withcommunication with the onboard systemestablished, and all of the units essentialfor attitude control, computer, propulsion

1 Year In Orbit

ESOC

MISSION OPERATIONS CENTRE (ESOC)

OBSERVATIONPLAN

RAWDATA

FLIGHT DYNAMICSSYSTEM

INTEGRALMISSION CONTROL

SYSTEM

INTEGRALSIMULATOR

INTEGRAL SECURE DISTRIBUTION SYSTEMS (ISDS)

INTEGRAL SCIENCEOPERATIONS CENTRE (ISOC)

INTEGRAL SCIENCEDATA CENTRE (ISDC)

INSTRUMENT ON-BOARDSOFTWARE IMAGES

PI INSTRUMENT TEAMS

SCIENCE COMMUNITY

ESTEC UNIGENEVA

SCIENCE GROUNDSEGMENT (SGS)

LONG/SHORT TERMOBSERVATION PLANNING

OPERATIONS GROUNDSEGMENT (OGS)

REAL-TIME + OFF-LINESCIENCE PROCESSING

PROCESSEDDATA

OBSERVATIONPROPOSAL

GOLDSTONE REDU

The Integral Ground Segment architecture

The Main Control Room at ESOC in Darmstadt on launch night

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PerformanceVerification

The payload group had satready in the Payload ControlRoom at ESOC eagerlyawaiting the launch. Afterseven years of work that hadincluded many highs andlows, they were at the point

where all the verification and carefulplanning came down to a simple andbasic question: Would it work?

After the highly successful chain ofevents covering launch, stage separationand orbital deployment, as the solararrays deployed the computer displaysshowed the electrical current increasingsteadily as the panels collected more andmore sunlight. At last the power was on,allowing the system team to monitor thehundreds of parameters and confirm theflawless activation of all units. All sub-systems were nominal and the spacecraftwas in its right orbit and had the correctattitude. Integral’s instruments were still‘sleeping’, however, and it would takeanother three weeks to bring them all tolife.

The activation of the instruments hadbeen planned to the last detail. Thenecessary procedures were in place andhad been carefully rehearsed by theMission Operations team together withthe scientists and technicians responsiblefor each instrument.

First, the instrument electronics werepowered up to stabilize the thermalenvironment on the spacecraft. The firstinstrument to become operational wasthe radiation monitor, IREM.

The next instrument to be brought to lifewas the Optical Telescope. With its

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valves and heaters, attitudeand rate sensors switched on.The spacecraft attitude was‘safe’, with initial rates almostat zero, and a few degrees off Sun-pointing, which thecontroller promptly recoveredwithin a minute. The launchinhibits were all cleared and a quick real-time analysis of the telemetry showed that the powerand thermal subsystems were alsofunctioning correctly.

In the meantime, Flight Dynamics hadreceived the orbital element data fromMoscow and had begun analysing themto compare the Russian predictions withtheir own. An exceptionally good orbitalinjection manoeuvre had placed Integralinto the desired orbit with just very smallerrors.

Anxiety remained high at the ControlCentre as the time for solar-arraydeployment approached. The arrayrelease sequence initiates, automatically,ten minutes after separation, butcontingency procedures are readied, justin case…

The thermal knives were activated andthe two solar panels gradually deployed.There was a mixture of relief and

satisfaction as the current from the firstarray began to increase. Eventually, thearray status telemetry changed too, asthe panel latched and its telemetryindicated ‘deployed’. Four minutes later,the second panel was also out. We had power and began acknowledgingcautiously that things seemed to begoing exceptionally well.

The background noise in the controlrooms increased suddenly as peoplebegan shaking hands and patting eachother on the shoulder. It is indeed one ofthe best moments in life when you canshake hands with your colleagues andsay: "We did it!"

The second-shift team left the scene toget some rest. There was still lots of hard work ahead, including criticalattitude-control operations, delicateorbital manoeuvres, convoluted onboardcalibrations, but also the feeling at ESOC

that Integral was going tobe a superb mission.

The next few days wereequally successful, as theorbit’s perigee height wasraised in several burns fromthe initial 651 km to thefinal perigee altitude of9000 km. The parameters ofthe final orbit turned out tobe extremely close to theexpected values.

The instrument teams in the Payload ControlRoom at ESOC, during the activation of the firstinstruments

Achieved versus expected orbit parameters

PARAMETER ACHIEVED ORBIT EXPECTED ORBIT

Semi-major axis 87 731.5 km 87 678.14 km

Eccentricity 0.824 148 0.813 202

Inclination 52.246° 51.6°

Perigee Height 9049.6 km 9000.0 km

Apogee Height 153 657.2 km 153 600.0 km

Orbital Period 72 hours 72 hours

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1 Year In Orbit

Proton counting rates measured by the IREM instrument from switch-on until mid-November. ‘Spikes’ occur during each perigee passage as Integral transits theradiation belts. The reduction in the proton flux by almost three orders of magnitudefrom the initial transfer orbit to the operational orbit is evident. The broad featurearound 10 November is associated with solar activity(Courtesy of P. Buehler and the IREM team)

First image of an X-ray star, Cen X-3, obtained with the Joint European Monitor for X-Rays (JEM-X). The star is the small black dot near the centre. Although maybe

unimpressive, the image provided the confidence that the instruments are capable ofdetecting and accurately pinpointing X-ray sources in the sky

(Courtesy of the JEM-X team)

‘First light’ for the Optical Monitoring Camera(OMC) just after the opening of the cover. The

brightest star is Gamma Trianguli Australis(Courtesy of the OMC team)

Gamma TrianguliAustralis (V=2.87)

Center of the image:RA: 15h 13m 48sDec: -70° 07’ 52”Integration time 10s

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successful check-out on 21October - voltages, dark current,bias signals and focal-planetemperature all nominal - weneeded only to open the frontprotective cover to see the sky.One of the scientists haddisplayed on a laptop an image ofthe part of the sky to which Integral waspointing and which he expected theOptical Telescope to see. The commandwas given to open the cover, and it took afew minutes for the wax to melt and torelease the cover mechanism before theswitch position indication displayed onthe monitor changed to ‘open’. After a fewseconds of integration time, the acquiredimage was downloaded via thespacecraft’s telemetry system to theground station in Redu (B), then sent tothe ESOC Control Centre and to thescientists’ screens. It was the sameportion of sky that our smiling scientisthas on his laptop, the same stars, thesame positions. One star among themwas particularly bright, namely GammaTrianguli Australis.

On 27 October the next instrument, theX-ray monitor JEM-X, was activated. Thehigh voltages of one of the two units(JEM-X1) were slowly increased in severalsteps and two days later the same wasdone for the second detector, JEM-X2,while the satellite was pointing to anempty field. Within a day, an image of thesky was generated by the JEM-X and ISDC (Integral Science Data Centre) teams– testament to the good state of thescientific analysis software. Since therewere no bright X-ray sources in this partof the sky, it showed exactly what wasexpected – an empty image! The JEM-Xteam had to wait another 2 days until thesatellite pointed to a part of the sky thatcontained a bright X-ray source, beforethey could be confident that the

instrument was working totally asexpected. This occurred on 1 November,when Cen X-3, a neutron star with amassive companion, was observed.

Unfortunately, Cen X-3 was in eclipse formost of the observation and the sourcewas only prominently visible towards theend of the observing period. Never-theless, the sky-maps for both JEM-Xdetectors showing the source wereavailable the next day. After JEM-X hadswitched off twice, triggered by anonboard IREM broadcast message due tothe high radiation environment on thedescending part of the orbit, it wasdecided to adjust the critical operationaltitude (when the instruments areswitched on and off ) from 40 000 km to60 000 km for the descending portion of subsequent revolutions.The altitude atwhich Integral exits and enters theradiation belts evolves with time, and istherefore continually monitored by theIntegral Science Operations Centre (ISOC).

On 7 November it was recognised that asmall number of anodes from each of thetwo JEM-X detectors were sufferingdegradation. The detector high-voltagesettings were lowered by 80 V, whichreduced the damage rate significantly. Inthe following weeks, only three furtherdegraded anodes were found on JEM-X1and none on JEM-X2. As a precaution, theJEM-X1 high voltage setting was reducedby a further 20 V on 10 December and theinstrument has operated flawlessly eversince.

The activation of the Integralspectrometer (SPI) was next andwent very smoothly. Shortly afterswitch-on of the SPI anti-coincidence system (ACS) thefirst gamma-ray burst (GRB) wasobserved by the ACS on 27October at around 08:34 UT, and

was named GRB021027. This confirmedthe SPI ACS system’s ability to trigger onGRBs. The burst was quickly seen in theoverall ACS counting rates with a 50 mstime resolution. On 4 November thedetector array had cooled to 117 K andthe high voltages of the SPI detectorswere switched on for the first time inspace. Two days later they reached theirnominal operating temperature (89 K)and the SPI’s performance could beassessed. All the germanium detectorsshowed excellent performance (with anenergy resolution between 2.3 and 2.6keV (FWHM) at 1.11 MeV, as expected),with the exception of one detector, whichhad a slightly lower performance (3.2keV), typical for degradation by pollution.During the first SPI annealing in February2003 this pollution was cleaned out, andthat detector’s performance recovered toits pre-launch value.

"Slowly, but steadily the first images maketheir appearance on our screens, first thebackground and then exotic objects. Wavesof energy coming from everywherematerialize on our screens.The window to aUniverse of explosive ghosts is open." Giuseppe Sarri

The Integral imager (IBIS) is perhaps themost complex instrument onboard thesatellite. It consists of two detector layers– the upper layer (ISGRI) is sensitivebetween 15 and 500 keV and the lowerone (PICsIT) between 200 keV and 10MeV. The PICsIT detectors were activatedon 20 October and the first ISGRI detector

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four days later. IBIS data acquisition wasperformed from then on, wheneverpossible, in order to gain experience ofoperations, although the high voltages ofthe veto modules were not enabled untillater. Finally, on 7 November, all the vetomodules were switched on and theinstrument operated in its nominalconfiguration for the first time in space.The whole team roared their approvalwhen it was clear that IBIS was alsoworking properly, with a performance inline with pre-launch expectations.

However, now that the full complementof Integral instruments was beingoperated in close to their nominalconfigurations, it became clear that therewas insufficient telemetry capability totransmit all the scientific data beingproduced. When checking out theinstruments, higher telemetry wasrequired by IBIS and SPI in order tooptimally tune the onboard eventselection filters. During a period withhigher telemetry allocation and whenPICsIT was operated in photon-by-photon mode, a gamma-ray burst (GRB)occurred within the IBIS field of view. Theinstrument and the ISDC team reactedquickly and the burst location wascommunicated to the astronomicalcommunity the next day. It is importantthat accurate GRB positions are quicklycommunicated in this way as it allowsother astronomers to search for theshort-lived X-ray, optical and radioafterglows. To the relief of the Integralscientists, the initial burst position wasconsistent with that derived much laterfrom triangulation using the Inter-

planetary Network of spacecraft. Thisresult was a milestone for Integral,demonstrating its fine imaging andtiming capabilities and the ability torespond quickly and accurately to eventsoccurring in the sky.

The transition from the instrumentactivation and commissioning phase tothe performance and verification phasewas gradual, and began on 15 Novemberand lasted until 6 December. During thisperiod the instruments mainly observedthe Cygnus region of the sky in ‘staringmode’. On 9 December the first ditheringobservations were successfully executed.The performance and verification phasecontinued until 30 December. During this

time simultaneous observations weremade with other high-energy missionssuch as ESA’s XMM-Newton and NASA’sRossi X-ray Timing Explorer (R-XTE),showing that the instrument calibrationsperformed on the ground were close towhat was being observed in space.However, the Integral astronomers had towait until February 2003 until the CrabNebula ‘standard candle’ was observedbefore the calibration could be confirmed.

All of the Integral observations made inthe 17 - 30 December period were madepublic and quickly placed into the ISDCscience archive, allowing many eagerastronomers to get their hands on theirfirst Integral data.

1 Year In Orbit

First data collected by the IBIS/PICsIT detector. The diagram atthe top left shows the distribution of the events on the detector

and at the right the associated detector spectrum for theseevents. The corresponding shadowgram images at low, medium

and high energy are shown below (from left to right,respectively)

(Courtesy of the IBIS team)

PICsIT detector shadowgrams for single (left) and multiple (right)events. They shows how efficiently the VETO system reduces

background noise by suppressing events entering the detectorfrom behind. In this case, 3 or the 8 modules had their VETO

system switched on (Courtesy of the IBIS team)

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Operations Summary

Both the ground and space operationssegments were active from the beginningof the mission. Despite some initialproblems, operations have beenconducted with high efficiency with, forexample, 97.3% of the slewing manoe-uvres executed as planned. The onlymajor changes to the ground segmentwere made to support an on-board changeto the Integral software, which allowed25% more telemetry to be transmitted toground. With this change Integral couldtransmit all the necessary science tele-metry, so mitigating the earlier problemshighlighted once the full complement ofinstruments were operational.

The performance of the space segmenthas remained good and the spacecrafthas not exhibited any anomalies thatcould not be handled by the groundteams. As is only to be expected withsuch a complex mission, changes to theconfigurations and operational proceduresof the various instruments have beenimplemented to take into account ‘in-space experience’, including five patchesto the onboard software.

The ISDC is routinely providing data andprocessed products to observers within 6 weeks of their observations – aremarkable feat given the complexityof the Integral data. For more detailedanalyses, the ISDC also provides acomplete set of analysis software thatcan be installed on the user’s owncomputer.

Spacecraft Platform

All the Service Module subsystemscontinue to operate nominally andthere have been no major anomalieson any unit. There has been no

emergency Sun re-acquisition so far. Fullredundancy is still available, with fullsolar-array power and no degradationidentified. There have been periodiccalibrations of spacecraft thrusters andsensors to improve operational efficiency.

Eclipses

Two eclipse seasons have been experiencedso far. In the winter season eclipsesoccurred during revolutions 26 to 35, andin the summer season during revolutions84 to 92. All subsystems performednominally during these periods. Themaximum depth of discharge experiencedby the batteries was low, at 21.5% and27.29%, during the two eclipse seasons.

Fuel Consumption

The fuel consumed so far is 366.9 kg, froman initial 541.9 kg. 359.9 kg was usedduring the Launch and Early Orbit Phase(LEOP) mainly to raise the perigee height.This left 181.9 kg for operations. Theaverage usage of 0.7 kg/month sincethen has been for reaction-wheel biasing.There is currently 174.9 kg left for futureoperations – enough for more than 15years at the current rate of consumption.The figure below shows the rate of fuelconsumption since the final orbitmanoeuvre.

Instrument Calibration Activities

The main Integral calibration target forthe high-energy instruments is the CrabNebula.This is a bright high-energy sourcewhose properties change only slowlywith time. It has been observed by nearlyall the high-energy missions flown and isused for comparing results from onemission to another. Integral has observedthe Crab Nebula twice, from 7 to 27February and from 14 to 17 August 2003.Integral will continue to observe the CrabNebula every ~6 months in order tomonitor the stability of the instruments.

Due to radiation damage to the SPI’sgermanium detectors, it is necessary toanneal, or bake them out, approximatelyevery 6 months. The first annealing tookplace between 6 and 13 February 2003and the second between 18 and 24 July.These have enabled the SPI’s energyresolution to be maintained to within15% of its pre-launch value. The ability toanneal in space is a first for this type ofinstrument, able to measure the energyof a gamma-ray to 1 part in 500.

The OMC’s calibration is maintained byso-called ‘flat field’ observations. Internallight sources are used to illuminate theCCD detector, allowing the instrument’sresponse to be quantified across the

detector plane. It is important thatthere are no bright stars in the field,so that the intrinsic response can becleanly measured. The best pointingdirections for flat fielding are chosenby the OMC and ISOC teams. Sevensuch ‘flat field’ calibrations have beenperformed by the OMC team.

Space Operations

Fuel consumption during the routine mission operationsphase (since the final orbit manoeuvre)

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1 Year In Orbit

The Integral Science Data Centre (ISDC) buildingin Versoix, Switzerland (above right). Right, the

computer screens in the Operations Room.(Courtesy P. Kretschmar, ISDC)

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During the first year in orbit, the timeavailable for Integral science operationswas divided between the core programme(35%) and general programme (65%).

The general programme time is open tothe whole science community, who can submit observing proposals. Anindependent Time Allocation Committee(TAC) then evaluates the proposals anddetermines which are to be performedbased on scientific merit. The coreprogramme is reserved for the membersof the Integral Science Working Team(ISWT) in return for their contributions tothe mission. The ISWT is composed ofinstrument and data-centre principalinvestigators, mission scientists, theproject scientist, and representatives ofthe US and Russian scientific communities.This ‘core programme’ observing time isused mainly for survey-type activitiesincluding regular scans along theGalactic Plane (GPS) and deep exposuresof the central radian of the Galaxy(GCDE).

The GPS consists of a sawtooth pattern ofobservations along the visible parts of

the Galactic Plane, in order to search fornew and unexpected events (see abovefigure).

The GCDE observations consist of fourdifferent grid patterns covering theGalactic Centre region from –20 deg to+20 deg in galactic latitude and –30 degto +30 deg in galactic longitude. The fourgrids, shown in the figure below, areexecuted twice a year.

Science Operations

The Galactic Plane Scan strategy. Integral performs scans in asaw-tooth pattern along the Galactic Plane once every 12 days.The saw-tooth patterns of two consecutives scans are shifted by27.5 degrees. The inset top centre shows the sizes of the fullycoded fields of view for the four Integral instruments

The Galactic Centre Deep Exposure is one of the elements of theIntegral Core Programme. It consists of four different overlyinggrids covering the area around the centre of our Galaxy. The leftimage shows the pointings performed twice within the first yearof the mission. The right image shows the exposure map for IBISafter the grid pattern was executed once. (Courtesy of E. Kuulkers, ISOC)

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1 Year In Orbit

Below is a graphical representation of thestatistics of scheduled observations fromrevolution 26 (30 December 2002) up torevolution 119 (7 October 2003).The totaltime available to science in this periodwas around 20.7 million seconds, fromwhich 19.7 million seconds of scheduledscientific observations have taken place.This corresponds to around 95% of thetotal time available to science. Thedistribution of the scheduled timeamong the various types of observationsis as follows:

During this period 67 observations havebeen made of 54 approved targets (notincluding GPS and GCDE surveys). Inorder to obtain maximum science whenobserving a target there are threepossible ways to perform an observation.Integral can constantly point at a targetat the centre of the instrument’s field ofview (so called ‘staring’). Alternatively, it ispossible to perform a small scan aroundthe target, which is called ‘dithering’.There are two dither patterns possible: a7-point hexagonal pattern or a 25-pointrectangular pattern. Dithering improvesthe sensitivity of the SPI instrument, butdecreases that of the X-ray monitor.Observers are allowed to choose theappropriate pointing mode for theirobservations. The figure top right showsthe pattern and the relation to theinstrument’s field of view.

The sky map shown below indicateswhich areas of the sky Integral has beenobserving (up to revolution 100, whichended on 11 August 2003) and theamount of time spent.

Distribution of the Integral observing time between thedifferent observation categories. 19.7 million seconds ofscientific observation time was scheduled in the period from 30December 2002 to 7 October 2003. 10% of the time was usedfor calibration purposes, 59% to observe targets from the AO-1open time programme, and 31% to execute the CoreProgramme elements (GCDE, GPS and pointed observations)

The different dither patterns - staring,hexagonal and 5x5 - used by Integral.

The position of the fully coded fields of viewof the four Integral instruments is overlaid

when pointing to the central position, i.e. whenthe target is on-axis

The Integral whole-sky exposure map (IBIS fully coded field-of-view) in galactic coordinates for the satellite’s first 100revolutions. The integration time is colour-coded according to thescale on the right(Courtesy of N. Mowlavi & M. Türler, ISDC)

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Many of the early Integral scientificresults have been published in 75 papersin a special edition of Astronomy andAstrophysics, issued in November 2003.Given the complexity of the data-analysistechniques required for the coded-maskinstruments, the low signal-to-noiseratios inherent in gamma-ray astronomy,and the fact that the Crab Nebula‘standard candle’ was not observed untilFebruary 2003 due to solar aspectviewing constraints, these results amplydemonstrate Integral’s potential tocontribute significantly to solving manyof the outstanding issues in high-energyastronomy. Some highlights aresummarised below.

THE CRAB NEBULA

Observations of the Crab Nebula - thestandard candle of high-energy astronomy- are essential for the verification of theresponse models of the high-energyinstruments. The Crab Nebula is theremains of a massive star that explodedin 1054 AD and left behind a tiny rapidlyspinning neutron star. A neutron starcontains the mass of the Sun, but

compressed into a tiny ball only 20 km indiameter. The neutron star in the CrabNebula is spinning 33 times each secondand produces flashes as the beamedemission sweeps though the line of sightto the Earth. The neutron star’s spinperiod varies in a predictable way andprovides an excellent tool with which toverify the timing capability of Integral.Observations of the Crab Nebula haveenabled the Integral astronomers toachieve both goals.

The figure below shows the pulse profileof the Crab pulsar in four different energyranges measured by IBIS. Two pulses arevisible connected by a bridge of emissionbetween them. The absolute phase of the light curve was determined to anaccuracy of 40 microseconds. Obser-vations of other gamma-ray sources willbenefit from this high absolute timingaccuracy of Integral. In the case of theCrab pulsar, the phase shifts between the light curves at different energies

Science Highlights

The pulse profile ofthe Crab Nebula.Each panel shows theprofile in a differentenergy range asmeasured by IBISduring the February2003 observations(Courtesy of A. Segreto and theIBIS team)

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can be used to constrain the three-dimensional structure of the radiation-producing sites in the pulsar magneto-sphere.

GALACTIC COMPACT SOURCES

Integral has already detected at least 12new, strong high-energy galactic sources,all of which have been quickly reportedto the astronomical community to allowfollow-up observations in differentwavebands. As a result, there is a greatdeal of interest in Integral within thehigh-energy astronomical community.The first of the 12 sources, IGR J16318-4848, revealed a highly unusual, line-rich,strongly absorbed spectrum in an XMM-Newton follow-up observation. Thesource was hardly detectable by XMM-Newton below 5 keV due to the strongabsorption, while being an intensesource in the Integral energy range. This,and the detection of similar sources by

Integral, suggests the presence of apreviously unknown class of highlyabsorbed objects. Another of these new sources, IGR J16358-4726, was foundto exhibit pulsations with a period of5850 seconds during a serendipitousChandra observation. It is unclearwhether these pulsations represent thespin or orbital period of the system.During a recent observation of theGalactic Centre region, Integraldiscovered a new transient source calledIGR J17544-2619. Details about thesource, including its position, werequickly sent to the astronomicalcommunity. The first mission to respondwas XMM-Newton, which managed tomake a Target of Opportunity observation,even while Integral was still observingthe source.

The good coordination between Integraland XMM-Newton, ESA’s other high-energy mission, is clearly an asset to the

scientific community, enhancing thescientific returns from both missions.

The flexible Integral observing strategyhas allowed the mission to respondquickly to interesting and unexpectedevents. Outbursts from a number of X-raybinaries, such as GRS 1915+105, XTEJ16550-564, SGR 1806-20, H 1743-322and GS 1843+009, have triggered Targetof Opportunity observations. Theobservations of the black-hole candidateGRS 1915+105 were particularly complexbeing part of a simultaneous multi-wavelength campaign involving Integral,R-XTE, the ESO NTT, the Ryle telescope,NRAO, the VLA, and the VLBA. It is bycombining results all the way from radioto the gamma-ray wavelengths thatastronomers hope to understand thenature of this microquasar – a stellar-mass black hole accreting from a nearbycompanion star and producing relati-vistic jets.

1 Year In Orbit

IBIS/ISGRI image of the areaaround the centre of ourGalaxy in the energy range 20-40 keV. The image covers aregion of approximately24x30 degrees. The manysources visible in the imagedemonstrate the richness of the Integral data.(Courtesy of A. Paizis andcollaborators)

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GAMMA-RAY BURSTS

A total of six confirmed GRBs have beenobserved in the fields of view of thegamma-ray instruments in the first 11months of Integral operations. This iscomparable to the pre-launch estimate ofapproximately 10 to 20 per year. Theautomatic Integral burst-detectionsoftware, running at the ISDC, provides~5' source location accuracy within ~15seconds of a GRB event. These alerts arequickly disseminated to the astronomicalcommunity for follow-up observations.Probably the most interesting of theGRBs so far is GRB030227 (see figure).Theaccurate determination of its positionallowed rapid follow-up observations inother wavebands. These revealed afading 23-magnitude optical counterpart

while XMM-Newton, observing only 8 hours after the burst, detected a fadingX-ray counterpart and provided a high-quality spectrum. Light curves of aroundone GRB per day are provided by the SPIACS. The precise timing provided iscombined with results from othermissions as part of the InterplanetaryNetwork to provide accurate GRBpositions.

DIFFUSE GAMMA-RAY LINEEMISSION

The measurement of the properties ofline emission from newly formedelements such as 26Al, 44Ti and 60Fe is oneof the key goals of Integral. The high-resolution spectral studies allowed byIntegral reveal information about

sources, through Doppler broadening,and their location, through shifts fromgalactic rotation.These emission lines arefaint and are distributed over largeregions of our galaxy, so that longexposures are required to map and studytheir properties. Early results suggest thatIntegral is very well suited to this task.

The detection of specific lines shows theSPI instrument’s ability to detect gamma-ray lines, even with modest exposures.Already, from just six months of data, thespectral-line resolution is comparable to,or even surpasses, the CGRO results afterits nine-year mission. This opens upexciting possibilities for more detailedstudies of this line as the Integral missionprogresses.

30

20

10

100 90 80 70

DEC-CAR (degrees)

RA-CAR (degrees)

An SPI image in the 20-200 keVenergy band showing both theCrab Nebula and the Gamma-Ray Burst (GRB) on 27February 2003 at 08:42 UT.This was the fourth GRB tooccur within Integral’s field-of-view. The image was generatedfrom only 18 seconds of data(Courtesy of V. Beckmann(ISDC) for the SPI team)

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The first six months of observationsalready hint at the presence of the 1172and 1332 keV lines from 60Fe in thedirection of the Galactic Centre. Since60Fe and 26Al are probably produced indifferent ways, the 60Fe/26Al intensityratio provides important information onthe contributions of the different sourcesto the production of 26Al. The ReuvenRamaty High-Energy Solar SpectroscopyImager (RHESSI) has recently measuredan 60Fe/26Al intensity ratio of about 15%,consistent with the value expected ifexploding massive stars contribute mostof the 26Al. The 60Fe lines were onlydetected at moderate confidence byRHESSI, and so Integral will be crucial inproviding the first solid detection of 60Fe.Searches for 44Ti line emission (at 68, 78,and 1157 keV) are continuing. 44Ti has ahalf-life of only 60 years, and so itsdetection would be a sign of anextremely recent exploded star, or

supernova, perhaps hidden by dust thatblocks all but the most penetratingphotons.

Another high-priority Integral target isthe detailed mapping and spectroscopyof the 511 keV electron-positron anni-hilation feature seen from the centralgalactic region. An initial analysis of SPIresults indicates that the 511 keV line hasa width of 2.95 keV, at the upper range of

previous measurements. The origin ofthe positrons (anti-electrons) is uncertainand neutron stars, black holes, super-novae, novae, Gamma-Ray Bursts (GRB),different types of stars, and cosmic-rayinteractions with the interstellar mediumhave all been proposed. Detailedmapping of the emission will provideconstraints on the origin of the positrons.Early results from SPI reveal a sphericalgalactic bulge that may be slightly offsetfrom the Galactic Centre. As yet, there isno evidence for the disk component seenby the OSSE instrument on the ComptonGamma-ray Observatory. However, withthe amount of data available so far, theupper-limit is still consistent with theintensity measured by OSSE. As moreobservations of the Galactic Centreregion are performed, it is expected thatIntegral will produce maps withunprecedented spatial and spectralresolutions and sensitivity.

1 Year In Orbit

Map of the Galaxy obtained with CGRO-Comptel (1991-2000) inthe light of the 26Al line. The insets show the clear detection ofthis line from the centre of our Galaxy and from the Cygnus areawith Integral’s SPI instrument after the first months of operation,demonstrating its ability to detect gamma-ray lines even withmodest exposures(Courtesy of the SPI team)

SPI spectra of the 1809 keV line emission from the Cygnus andGalactic Centre regions, produced by the decay of the radioactiveisotope 26Al (with a half-life of approximately one million years).

Massive stars are a probable site of formation of 26Al, and thismakes it an ideal historical tracer for nucleosynthesis. The

observed line intensity is consistent with previous measurements,but is narrower (with a 3.1 keV width) than the 5.4 keV width

reported recently by the GRIS experiment

1800 1804 1808 1812 1816 1820 1824

Energy (keV)

Inte

nsity

(10-

4p

h cm

-2s-

1ke

V-1

)

1,5

1

0,5

0

0,5

-1

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The second Integral Announcement of Opportunity was open between 15 July

and 5 September 2003 for proposals for observations to be performed during the

second year of the nominal mission. The total number of proposals received was

142, requesting a total observing time of 144 million seconds. Given that roughly

18 million seconds are available for the open-time programme during the second

year of the mission, this is an over-subscription by a factor of eight.The extremely

high degree of over-subscription shows the continued high degree of interest in

Integral from the scientific community. Combined with the encouraging early

results emerging from Integral data analysis, and the fact that the satellite is in an

excellent state (there is still fuel for more than 15 years of operation), there is

great hope that the Integral mission will be both long and highly successful.With

this in mind, plans are already underway to request an extension of the mission

until the end of 2008. Should such an extension be approved, it is planned to

move the ISOC from ESTEC to ESA’s VILSPA facility in Spain, to benefit from co-

location with the XMM-Newton Science Operations Centre.

The excellent mission status and the scientific results available so far would not

have been possible without the combined efforts of all parties involved – all of

whom did an outstanding job.This includes the industrial consortium, the Proton

launcher team, the Project Team, the Mission Operations Centre (MOC) team and

all the scientists from the instrument teams, ISDC and ISOC. We thank them all

and look forward to even more exciting results from Integral in the future.

Second Announcement ofOpportunity and Future Plans

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1 Year In Orbit

The Integral Team assembled at ESOC, inDarmstadt (D), on the day before the launch, witha quarter-scale model of the spacecraft

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The International Gamma-RayAstrophysics Laboratory- 1 Year in Orbit

Contact: ESA Publications Divisionc/o ESTEC, PO Box 299, 2200 AG Noordwijk, The NetherlandsTel (31) 71 565 3400 - Fax (31) 71 565 5433Visit ESA Publications at: http://www.esa.int

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