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The Low-Energy Experiment on EXOSAT

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The Low-Energy Experiment on EXOSAT 4 :a-;-ril-;vit 7h- .'feii^. -1::?^:.' Uxpeî inen: for CXOS/iT J..-Î. H::;";~n.i<-_, Jni:*-vsiu< of Leicester TV- Lew iJr.eisy i'.ioe: ircr.:.: on IJXOEAT J.A.-l. 3:\-L-^-.->, ->STIC *<;;< Working Group, Leiden Low briefly :'po^trû£copy with EXOSAT J.,i..\\ Slceïei; Cosmic hay Working Group, Leiden lun.-.r C.- ii : a: I':n of Point X-iay Sources Optical iJer.-ificatio:. of X-rav sources ."f./. P^>:;4- ••ij .L.si;aL Greeriuie'-i Observatory lder:tH::ôt."-. of »ray Sources with Radio Dbiecr: The Precise Location of •ray Sources ard their Identification, with Infra-red Objects •\ •X-chialini-iHl'Jorth, Pulsating ar.d Binary \~rv: Sources E.P.J, van den Heuvei, University of Amsterdam and Brussels Source Structure via the Occultation Technique A.C. ?abiar.t Institute of Astronomy, Carnbridae Spâtiai Structure in Galactic X-ray Sources C.A. Ilovazshj, Meudon Observatory The Structures of Extragalactic X-ray Sources M.S. longair, Itullard Radio Astronomy Observatory, Cambridge X-ray Halos H. Spiegelhauer and J. Trumper* University of Tubingen Proposals for tl.e DCOSAT Observation Programme and Choice of Orbit F..D. Andres&i, F.5R0 The experiments to be carried will be funded by LTr:", -Î:.-.: will : •• produced by a small number of research groups, while the ;;-.-': It i~. •. will be distributed among a much wider comnurii* v> fnLb-v.'ir.^ •:.-_• selection of proposals for -he observation program--:-. In 1974 '•he Scientific Programme Board approved thf- :i--:^:"i ;• : experiments satisfying the principal mission ob^ec" Lve.- à.:.: - .• study of some experiment options which would provl:« .=:. ir.3p:..r capability and spectroscopy in the low energy rang-' ar. I .ir. .•:•"••:. |.. of the upper limit of the range 10 iiO k-V,'. In order to provide the European ^cientiric Conr.u:1.if." •.•;i':!i ::.-• latest information on the payload composition and ir. CM-iei : :> : • confident that all aspects of the scientific mission bad '.seer. -J:'--:. into account, it was considered that a colloquium weld prcvi-j-- *::•? most suitable forum for an exchange of views. The ecilo-.u lum entitled 'X-ray Astronomy and Related Topics' was held a' EST:!.', Noordwi]V, Holland or. February 25 and ?.<ô 1975, IT. spite of ! i~ ••-•: short notice, the colloquium was attended by some --.eventy s^i-.-r.-l .: encompassing the whole spectrum of astronomy. Since the colloquium, the Scientific Programme Board h.;s .jppi •"-•-: •. inclusion of the imaging telescope and high energy oprior.s a:.: • ;.• choice of th* 'northern orbit', which places the emphasis for •...- occultation mode on galactic X-ray sources. All speakers are thanked for their great efforts prior '-- an: :.:::. the colloquium and for providing the texts of their talk:; in ;•-•-:: time to Dr. R.D. Andresen» who was responsible for 'h^ ;.r-<-.i •:-.'. | • r- -. ariar. J. Taylor jH ;>;,-:tic X-rH.y bour-es. J. T . C'j'nanp. Urnven'itv Coll pr<* tnndon, r.ullara Cimnp Sf'en^0 L-ibcrr; ;iolmb'jr,v bf. Mary, Dnrk mf-| Surrey, Lr:r"lar<i. ABSTRACT The Uhuru catalogue sources may be classified bv ^-aj actio latitude into galactic and extra galactic populations. The galactic sources include a group of iii^Jjl.v luminous objects near the galactic renter, trie compact X-ra.y sources in binary systems «n;i tne X-ray emitting sunernova remnants, T-ie?re three cntegorie? of X—ra.y soufre are discusser, and ::npo cinr-y r.nurnc categories are bripHy rpferr"'! U>. ". IHTaOPUCTION fOiiOKiru. t:.e iauncninf of tne unuru an^ CorermcuF satellites, approximately 170 - idJ X-ra,y sources are now known to (-XJHI. While more recent observations by tne instrument? on UK-1, surest tnat a minority of X-ray p' •j.rzf^ may be transient in nature, we will for tne purr-osf;; of tn i R review continue to classify sources bv r--31 ••>."* ••^ 1st itMde. The Uhuru sky map, in falactic co-ordinates, is snown in I'i^rure 1. The large populat­ ion (about 100 J of bright galactic sources in appar­ ent at latitudes below 20 . It has been suggested by MatiLsk.v et al (1973) that with a few obvious except­ ions, sucn as Sco X-1 and. Her X-1, sources with b"1 20° are probably extra-galactic. A log N - ioç S plot prepared by lïiatilsky et al (1973J from the Unuru catalogue is given in Fig^ire 2. The faint nigh latitude sources fall on a line of slope - 1.34 + 0<,?0, a value which is consistent with - 1.5. These extra-galactic sources are the subject of another review (Lewin ) wnile their possible relationsnip io extra-raiacitc sources is discussed by Longair ( ). The low latitude sources form two groups in the log N - le*- s Dlot. X-ray sources of larçe flux appear to constitute a group of objects with a slopp of -1.5 ,1 ;r. r';rurr- ',-•. Tn ir. va • \^ : :-. *.riO <.- u '. u'. a r : L:«' l'or^-j tic u-. .-. Trie X-r«.v ::nectra of tner-'p rcurcf-" '\'iov. -'? <:ctrjr.cn r.cr.- vnv':r>r low rvarçy cut off >-;i Î n n , if :i'jp :.:• p.bscrr»" : ' "". by ' nterst*»1 inr i^?, reouire;-' trip orvets to be at tt distancr- of ''v.1 - U Kpc wnicn wo "J i <-* r .MCÇ T r- err ; r. T:JR reriori of the ralactic centre. T'^ir 1 urr. • r.o-- \ t ,•• WC^J' I - , -, -3^ -1 tnen De al.jit 1w errs sec In t'ip follovjjnp sectior:--, we w: 1 ; brirfly niscui-r the falfictic center sources and trier, examine t-r:e COTII'^Ï object binary sources in greater detail,, Tne cln^s of X-ray emitting supernova remnants LS not représenter: significantly in FArurp ?. and will be d - <-"u:.^en s^pirateiy. Finally some brief remar.Ks about sources in /'lcbu'.ar clusters and transient X-ray sources w,!' be presented. 2. Tne Galactic Centre X-ray Sources Prior to the launchinr of IJtiaru, X-ray astronomy was carried out almost entirely witn rocket borne instru­ ments, Durinr this phase of tnp subject, a rmup oï about ten sources in the general director, rf tne /-alactir center attracted considerable attention. Amonf tne most notable observations of this region were carried out by oennopper et al (1970) who located several of the X-ray sources with a precision of 1" - ?'. Kownv*>r . ; - *ir;;'t .- ' •' '• à'j:i* ' T '•' O :" "" •".' ~'Jt;* n-rr^rt.'' tO l,n('RP i-h.:"c-- : •.-.( r- net FV-CV.^FÏM'J : 1. Wh 1 * " m rotr-T-porrt t.n::- • v f.yr'ii'y s-.i*--* ^ PI n^ i 1' t.n» nou^noe- rpaU.v ar^ rinse tc tnp r:-ln.ciio center, infra red or radio ;-.ind:cia+e ch.ïerf- n;-.vr also r.'.i been lorRtPdo Trie most accuratp nonitional information for ore of im*;-e rources h:^ b*-pn obtained by Davison p+ a1. tl975) wno used tne KSSL instruments on the Conernicun satellite to obtain an error box of ^" by 7" for tiiP source 9x^-1 ( 3Ul','tJ^-2ci). Tnis observation was narrid ^ut by tnearis of the lunar occultation technique. Firure H from the work of Davison 0973} snows the size arui location of tnp 9^ error ellipse to^etner witn the POPXLÎOIÏS of a number of nearby optical and radio source?. Unfortunately even witn an error box of this size, no compelling candidate object emerges. This su^T^Fts tnfit positional data of few arc Fécond precision will eventually be reouired for identifications in this region. Because of the low energy cut off which is observe"* in tne spectra of the galactic center sources, X-ray optical systems will operate at a disadvantage and observations using lunar occultations or modulation collimators may be essential for position letsrmir.at inn in tnis part of tne galaxy. ,1 A1 thoufrn , wi ~U tne ex red. W>ri of ^;JI =*"•-.•;•- rer..r.••>.:. i it ic* possible in «t trie ^ainotic X-r-'.v srurcss ma;, al ! be r-nm^ct ob.ipctr in binary Kvitpmrj, it nan oe^r pointed out bv Ranley &nd Tuohy (147^) tnut -,otn tr.p :i i;*n 1 umincsi tv source? in tne Lar,-n l'j-.:£ " >.:.ir o.'.-i-.i and the ten rala^tic center sources do not '-cijn^p. I may ne tnerefore that tries & sources will Lpr-ome ini.^r- e^tin* a?iï:n in tr;^ f'i+ur*1. F^r tnr moment, it RPP*;^ tnat further progress renui^ps ^esitinna: utii= o;' ; orecinion that, can only be rrov'.îed by tc.f 1 una1" occultation trcnmque. 3. Coir, m ct A~ray Sources in binary 3y"ten-.r One of the mo.-t exciting results utt-uie! k" "; • WDS the discovery of a cLass of v^rinbi0 rniscti^ /-•-: sources wnicn. are tncufsit to be bmarv s.vf.teœs tn:-. ;. <-o a c oniric t co.iect • Thi F compact secondary can be e \ tr.p p- black hole or a neutron star. A-ray pmi?s'on is n-^ uced by the accretion of .natter from the primary st;;r onto the secondary. Tne X-ray luminosity is TY i G , jn_ uK ( 1 ;• K ' dt wnere K and R are the mass ani rauius of the ^omp^icr. object and dM/dt is the accretion rate. JvstemF of '•. sort can produce luminosities in the ranre 1j '"' - ... ,,T< ;- sec- and the source luminosities observed in both our cv.r. ralaxy ana the Large Magellanic Cloud j»e in t.m s ranre.
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