Berthelsdorf, R.

Brinkman, A.C.

Lemen, J.

Lund, N.

Olthof, H.

Pacault, R.

Reppin, C.

Rocchia, R.

Scheepmaker, A.

Taylor, B.G.

Leiden University Scholary Publications

Adv. Space See. Vol.2, No.4, pp.301—305, 1983 0273—1177/83/040301—05$03.00/OPrinted in Great Britain. All rights reserved. Copyright © COSPARX-80, A EUROPEAN X-RAYASTROPHYSICS MISSIONB. 0. Taylor’, R. Berthelsdorf2, A. C. Brinkman3,J. Lemen2,N. Lund4, H. Olthof5, R. Pacault6, C. Reppin7,R. Rocchia8, A. Scheepmaker9,H. Schnopper4,G. Spada’°,R. Staubert” and M. Turner’2‘European Space Agency, SSD,ESTEC,Noordwjjk, Netherlands‘Mu/lard Space ScienceLaboratory, University College, London,U.K.3SpaceResearchLaboratory, Utrecht, Netherlands4Danish SpaceResearchInstitute, Copenhagen,Denmark‘European SpaceAgency,RueMario Nikis, Paris, France6European SpaceAgency,FPSO, ESTEC,Noordwzjk,Netherlands7MPIfQr ExtraterrestrischePhysik, Garching, F.R.G.8Sectiond’Astrophysique,Centred’EtudesNucléairesdeSaclay,France9CosmicRay Working Group, HuygensLaboratory, Leiden,‘°IstitutoTESRE/CNR, Via de Castagnoli,Bologna, Italy“AstronomischesInstitut der Universität Tubingen, F.R. G.“X-ray AstronomyGroup, University of Leicester,U.K.The salient featuresof X-80, a EuropeanX-ray AstrophysicsMission, and a car4idateforselection as the next satellite in the EuropeanSpaceAgency’s scientific prograitma, isdescribed.I~r~DucrIaJ~ scI~rrE’Icoam~crivrsThrough UHUPJJ, Ariel V and }~AO-l, X-ray astronanyhasbeenestablishedasone of the nostexciting and productivebranchesof astrophysics. Outstandingresults havebeenrecentlyobtainedat longerwavelengthswith the telescopeof the Einstein observatoryand the Europeanmission DCOSAT, to be undertakenin 1982 through 1984, is expectedto make an extensivecontribition in enlarging the scopeof the subject.Ouly a limited numberof n~3itnnand high resolution spectroscopicobservationsup to - 4 keycould be carried out with Einstein. E~CSAT with its imaging telescopeswill undertakemediumandhigh resolution spectrosco~up to 2 key, andwith its medium energyexperimentandgasscintillator experiment,mediumresolution spectroscopyup to 35 key. However, a largeprograirmeof ~rk on the detailed study of spectraandvariability of X-ray sources (> liiJy)can now be identified for a successorof the Einstein andEXOSAT observatoriesusing new,sensitive instrun~ntationbut which doesnot require the power andcost of large imagingtelescopes.X-rays aregeneratedin high te~çerature(T > io6 K) plassas or by the interactions of highlyenergetic charged particles with magnetic fields or photons andare, in general,associatedwith sourcesandsituations in the Universewhich involve largeconcentrationsof energyorwhere large energy releasesare taking place.High resolution spectroscopyin the energyrange0.5—10 keypermits the study of the physicsof energeticcoronalandphotoionisedpiasnaswhich areknown to be presentin manyX-raysources both inside andoutside our galaxy. Measurenentsof Enission line intensities in theseplasnaswill allow estimatesof gas tenperature,density and ionisation state, elEnantalahundanceandgasvelocity to be made for objects suchas supernovar~trmnts,binary sourcesandclusters of galaxies.Variability on all measuredtimescalesis an alnostuniversal characteristicof both galacticandextragalactic sources,and study of which is a valuable tool for the investigationoftheir nature andenissionprocesses. It ranges fran the sub—millisecondquasi-periodicbursts exemplified by CygnusX-1 to the single outbirsts of bright galactic transient sourcesoccupyingmanynonths, and possibly never recurring. In bet~~eenthere is a wide variety ofbehaviour, periodic and aperiodic at all timescalesand intensities.Spectral features above satE 15 key have beendiscoveredin a number of sources,e.g. Her X-1.If the Her X-1 features are interpretedas cyclotron enission they nay provide a powerful tool301302 5. C. Taylor et cxl.for the study of the magneticfields of neutron stars. Many of the X-ray sourcesassociatedwith active galaxies exhibit very hard spectrawhich suggeststhat ntich of the X-ray luminositymay be found in the energy rangeabove 15 key.SCI~PIFICPP.Yl.OPDThe scientific aims of the mission require a canbinationof narrow field-of-view (FOV) instru-ments andwide—field instru~ents. The former allow the detailed study of spectraland tønçoralbehaviourof selected,kr~~nsources,while the latter enable long term nonitoring of galacticand extragalacticsources,as well as the positioning andt~np.ralandspectral study of highlatitude transientsandbursters. Theprincipal characteristicsof the nodel payload and itsvariants studied in the ESA phaseA study aregiven in Table 1. The instrumentcatiplatentincludes four Bragg Crystal Spectraneters(BCS) and a Phoswichdetector, togetherwith eithera LargeArea Proportional Counter (LAPC) or a Kirkpatrick—Baez Concentrator(K-BC) or a CodedMask Gas Scintillation Camera (C!I3SC) as the narrow field instrtznentsand four wide field-of-view Dicke or TransformCameras (WFC). A snall Ganina Ray Burst ~bnitor (GBM) is also included.Table I — X—8O Payload Characteri. ticsEnergy! Energy! Sensitive FoV Angular Source Confusiontnetrss,ent (Wavelength) (Wavelength) Area (cm2) (FWRZ) Resolution Limitsrange resolution FWHN Time(s) Millicrabs8cSLjF(200) Fe, 1.7—2.0 2.3 m~ 1440PETI S , 4.8—5.5 1 4.0 ml 930 oPET2 Si, 6.1—6.8 1 6.1 sI 695 6 . I —5flAP 0 • 18—22 I 92 ml 14702(a) LAPC 1.2—20 keV 192 at 6 6eV 2500 1.3° — ~ 50 ~ 0.32(b) K—BC 0.2—10 6ev 72 at Fe 4592atS 400 , , ,~ 4122 at Si 550 30 4 Ii 0.06202 at 0 7002(c) CMGSC(2) 2—30 6eV 92 at 6 6eV 700 3° ‘. 5’ ~ 1O4 . 0.063 Phosuich 15—200 4eV 302:at 20 6eV 650 4° —122 at 200 6eV4 WFC(4) 2—20 (imaging) 202 at 6 6eV 320 34° ~. 2’2—50 (timing) (each)5 08K 30—130 keV — 50 120° ~. 10’The Bragg spectraneteroffers goal spectral resolution in four narrow energy bandscentered onthe strongest X-ray lines enitted by highly ionised atansof the nost abundantspecies (oxygen,silicon, sulphur and iron), overa wide rangeof plasna tanperaturesfran - 106K to above 108K.Spatially resolvedspectral mapsof extendedsourcescan be producedwith a resolution of a fewminutesof arc.The LAPC array hasa large collecting areaand, hence, capability for sub—millisecondtiming onthe bright galactic sources. The instr~inenthasa low backgroundand a narrow field-of-view,andcan, therefore, study spectraandvariability in faint extragalactic sourcesdown to itsconfusion limit of 0.3 millicrabs on tiinescalesof secondsto days. With its noderateenergyresolution 1.2—20 keV, it carplesentsthe Bragg instnn~ntand~uld provide continuum measure-mentsover this range.Advances in the develorxnentof light-weight technologiesfor minor manufacturingand thedevelormentof imaging gasscintillator camerashave lead to the study of the Kirkpatrick-BaezConcentratorand the CodedMask Gas Scintillation Cameraas alternatives to the LAE~ in theX-80 context. Sinceboth instrunentshave imaging capability they can be used for spectralnapping. Their source confusionlimits ~uld be a factor of 5 lower than the LPPC. Sincegasscintillation proportional countersareused in both instruments, the spectral resolutionobtainable~uld be a factor of 2 to 3 better than the LAPC. Their lower areaof courselimitstheir capability for millisecond timing.The WFCs will be able to image the X-ray sky with an accuracyof a few arc minutes fran 2 to20 key in order to detect, locate andmeasureX—ray transient events. They will provide a veryefficient meansof nonitoring, on a regular basis, all bright X-ray sourceson timescalesofdays to years. CoordinatedobservationsbetweenX-80 andground observatoriesand indeedtheSpaceTelescopesheuldprove particularly fruitful. The WFCs can provide an alert to groundor other spacefacilities for transient—type~phenanena.The Ploswich will extend the range of the spectraland timing studies while the GBM, with itswide field of view,is intended to be capableof locating to a precision of about 10 arc minutes25 or so high luminosity gan8na-ray tursts expected per year.X—80, a European X—Ray Astrophysics Mission 303SPACBCRAF~ANDMISSI(~1PARPIMETERSThe mission can be readily undertakenon a free-flying satellite with n~estperformancerequir~nentson 3-axis attitude control (— 5 arc mm), attitude measur~ent(- 1 arc mm),averagedata rate (- 40 kbps), ix~er(- 350 W) andmass C- 1 tonne). The spacecraftwould belaunchedby Ariane into a 600 km circular equatorial orbit, the best that can be envisagedfran the backgroundpoint of view, and operatedfor a rnininun of 3 years. The spacecraftconfiguration is such that the Sun pointing faceof the fixed solar array can be offset by upto 30°fran the Sun vector yet still be providedwith adequatepower. The spacecraftis freeto roll a~utthe solar vector so that the co-aligned, narrow-field-instruments,viewingperpendicularto the solar arraynormal, can view anywherewithin a band on the sky, which is60°wide by 360°. The viewing bandrotates aroundthe sky with the Earth’s notion and thewhole celestial sphereis accessiblewithin a six nonth season. Thus, any sourcecan beobservedby the narrow field instrunentsfor up to 2 nonths at a time, every half year, andobservingis then only interruptedby Earth occultation. The optical axes of the Wide FieldCamerasare perpendicularto thoseof the narrow field instr~xnents.The fields—of-view of theWFCs are - 60°wide and the four camerasare arranged such that with a roll about the solarvector and the use of the 30°offset capability, a setof nine attitude menoeuvresis sufficientto allow an all-sky survey to be undertaken,excluding a coneof 300 half-angle centred on theSunX-80 PAYLOAD PEWO~4N~CHARA~ERISTICSAND C~SERVATIC~PRXR2~Mv1EThe power of the X-80 instri.rentationnay be judged fran theshort sequenceof diagrams.Figure 1 indicates the minixtum detectableiron line strength (5 sigma) with the BCS, the K-BCand the CXSC. Figure 2 indicatesthe minizlun detectablesource strength for the LAPC, WFCandCOS3SC as a function of integration time.:1 _K-BC~ l0~I I I 102 1o1 100 101 io2 1o~ io~ lo~io~ io’ io~ io2 10_i 100INTEGRATION TIME I SetondsI cm2 s~keV~1Fig. 1 Minimum detectableiron line strength Fig. 2 MinImum detectablesourcestrength(5o) as•a function of sourcecontinuumstrength (So) as a function of observation ti.ie for aat 6.7 key. Sensitivities arc shown as a Wide Field Camera, the Coded Mask Gas Scintil—function of observing ti.me (10’~sand/or lO5s) lation Cameraand the Large Area Proportionalfor the Bragg Spectraneter, the Coded Mask Gas Counter.Scintillation Camera and the Kirkpatrick—Baezconcentrator.Figure 3 shows a simulation of an X—80, WFC, observation of the galactic centre for 100 s.GX5-1(1127)~4U1813-140(588) ~ Fig. 3 Simulatedperformanceof the Wide4U1728-169)260 = Field Camerafor a 100 s observation of the4~~17i(3~9~_- galactic centre region. Incident source~GX 9.1(5%) Gx3.1L46~)~ intensities (millicrabs). are shown in brackets._____ The WFC mask in this simulation has 64 x 64- elenents yielding a 40’ resolution. Thex)20O)~ proposed instrumentwill have 512 x 512e enents yielding — 5 resolut3.on.—_.—-—~---o~————--~Sco X-2I715)25 1705-444(280):304 8. C. Taylor et al.Figure 4 showsa simulation of the residual enission line spectrumof CAS-A asobservedwiththe K-BC. The sensitivity of the ç4C to intensity changesis illustrated in Figure 5. Figure6 shows the sensitivity of the Phoswichdetector.24111 241SI8*~ I~I~ ~IV c11-4 . I8~V8TI8N TII~ •Il~4 IX~U~~22lIt 22~~~IcIs32lIIS 2* XIII O~~Y~ I—S ~V D~CY 1115E S-il te IllD lass.~1’Iss “S148Z 121114 1 121lii CXVIII11111ISISIS~II~)t8 XVII ‘SCa XIX 48~ ~ ~ I ...., 282151(4 ( I.. SU._.... ..... .~.. .I 18 32 41 84 11 IS lIZ 121 144 III 178 212 211 224 241 258PHP ENERGYCH~HHELS(48 eV/*)Fig. 4 Simulation of the residual aiiission line spectrumdevelopedby the Kirkpatrick-BaezConcentrator and gasscintillation focal plane detector for a 104s o servationof the CAS-A SNR.— IPHOSWICK2 ___________ —~ 10 I I I •. (INTEGRATION TIME‘I, s’~ 5 .i0~ SECONDS1MONTH SPAINT SOURCE AT HIGH ~ 10(1mCRAB( (0” MINUTES (22E23— 10 GALACTIC LATITUDES t MDC CRAB SPECTRUMI RIGHT-HAND SCALE IvsDAY ‘-z i..3 10 BRIGHT 10~I4IMJTES ~ .z ~SOURCEINb GALACTIC CENTRE b(1000mCRAB((LEFT HAND SCALEI~10_i . 102 MINUTES1 HOUR ~TELEMETRY LIMIT \ —— ~ 10-S.\ p—I____C I_i__I-2C 10 10 MINUTESz LIMITING SENSITIVITYz 2:U, a5 2:-3 I’s— 10 I — io~6 I I I I I0.1 1.0 10 10 20 40 100 200 400 1000FRACTIONAL CHANGE (N SOURCE INTEN~TY ENERGY 6eVFig. 5 Sensitivity of the Wide Field Camera Fig. 6 Mininun detectablesourcestrengthto changesin source intensity for abright as a function of energy for a 5 x ~ secondsource (i0~ntillicrab) in the galactic centre observationwith the Phoswichdetector. Theregionanda faint sai.rce (1 millicrab) at sensitivity with respectto the Crab aridhigh galactic latitudes. ~X 4151 is indicated.X—80, a European X—Ray Astrophysics Mission 305Table II indicates in a qualitative manner the relevance of the proposed instruments to thedifferent sourcetypes listed. Generally speaking targets will be examined by the narrowfield inetnuentsfor lO~-l0~seconds. Cn the other hand the minisrun observation tine will beof the order l0~ seconds, since the spacecraftwill not adoptnore than one pointing attitudeper orbit. A caplete sky survey to the i~.iJy level with the WFCs will require sane3 ~1ays.Table III outlines an observingprograinnefor a three year mission. It shouldbe tome inmind that sixnultan~sobservationsare possible, on different fields, with the narrow- andwide-field instruments. Given selection of the mission early in 1983, the satellite could belaunchedin 1987, and operatedto at least 1990. While it is anticipated that the instrumentswould be of the principal investigator type, it is intended that a significant guestobserverprograrmewould be rnplenented.Table II. Oii~atibility of the ProposedPayloedIAPC, Wide Table III. X-80, Medel Three Year MissionSourceType Bragg K-W, Phoawich Field ~ p~ograznnea~c ca~ras4x / “ / 1. 50 QSO’ a and active galaxies 400 days?Ive galaxy / “ / 2. 50 clusters of galaxies 200 dayscluste~ / / A 3. 50 X-ray bireries 200 daysBinary s~ 4. 50 active starsand coronae 100 days~sterX x / / / 5. 20 supernovarses~ants 50 daysTransient / / / / 6. Sky survey with w~~: 300 da sSNR - - (3 days every 10 days) yActive Sta1~ 1’ ~‘ 1 “ 7. Galactic centre regionwith WFC) 50 daysStellar ourona / / — —Bulgesourcex / / / /XSin.siltane~isground basedobservation ~rthwhilecannix~itorir~ividual galaxies in cluster~~FCcan provide alert to other observatoriesa~G~sThe authors,neErl2ersof the ESA X-80 Phase A Study Team, wish to acknowledgethe advicefranand manyuseful arid sti.nuilating discussionswith Drs. L. Culhane, L. Koch, A. PeacockandK. Pounds.

X-80, A European X-ray astrophysics mission

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X-80, A European X-ray astrophysics mission

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