PoS(Integral08)020 Γ -rays γ -ray mis- γ http://pos.sissa.it/ a ‡ erg/s. The observed emission is in agreement with the 33 10 × and G. Rauw b , R. Walter ab † ∗ [email protected] Speaker. FNRS Research Fellow. FNRS Research Associate. are expected through inverse Compton scatteringbeen of unambiguously the detected. copious UV radiation, butTo detect they had this never emission, observations performeding with advantage INTEGRAL of the were highsions. carefully analysed, spatial tak- In resolution of particular, this deepseveral energy hard bands, with X-ray leading respect to images the toThe of very hard previous first the X-ray detection emission region previously of detected of this by3 source BeppoSax Eta different at around Carinae Eta point energies Car up sources. were originates to from constructed The 100 atspectrum emission in least keV. unambiguously of analyzed. Eta Car itselfThe can X-ray emission be of isolated Eta for Car in thearound the first 22–100 1), time, keV and energy and range its its is luminosity verypredictions hard is of (with a inverse 7 Compton photon index models, andthe corresponds to collision. about 0.1% of the energyA available systematic in search for hard X-ray emission fromstars is other also colliding-wind being binaries performed and using from the massive INTEGRAL data archive, and the first results are presented. If relativistic particle acceleration takes place in colliding-wind binaries, hard X-rays and ∗ † ‡ Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. c

7th INTEGRAL Workshop September 8–11 2008 Copenhagen, Denmark J.-C. Leyder Hard X-ray emission from Eta Carinaecolliding-wind & binaries other Institut d’Astrophysique et de Géophysique, UniversitéINTEGRAL de Science Liège Data Centre, Observatoire deE-mail: Genève a b PoS(Integral08)020 , 2 ) c -ray / γ v ( ), where J.-C. Leyder : they can gain v : each time the particles v . 4 . Then, the observations of -ray emission from colliding-wind bina- 1 γ 2 ]. 3 , 2 ]. This is a variant of the original scenario suggested by Fermi , 3 1 , 2 , 1 the website of the High-Energy Astrophysics group from Liège . Finally, the hard X-ray emission expected from other CWBs is briefly 2 , and future prospects are offered in Section 3 , taken from (hence the name) [ 1 c ], where the particles collide with a “magnetic mirror” moving at speed Schematic illustration of a colliding-wind binary (CWB) system, represented at three different / 4 v Moreover, massive are early-type stars, and as such, they exhibit a strong UV radiation A colliding-wind binary (CWB) is a binary system consisting of two massive stars, each having The rationales behind the search for hard X-ray and or loose energy, although there isand a the gain process on is average. nowadays The known net as energy the gain second-order is Fermi proportional mechanism. to emission is expected from CWBs [ Figure 1: field. The combined presencethat the of inverse the Compton relativistic mechanism electrons can and take place, of thus the explaining UV why radiation a hard field X-ray implies and in 1949 [ moments along the .winds, and The varies with shape the of orbital the phase. shock depends on the respective strengths of the two a strong . These two(see winds collide, Figure leading to the formation of a hydrodynamical shock ries (CWBs) with INTEGRAL are presented in Section 1. High-energy emission from colliding-wind binaries are described in Section discussed in Section Hard X-ray emission from Eta Carinae & other colliding-wind binaries Introduction particle acceleration can takeenergies place. by the In first-order particular, Fermi electronsis mechanism can (or based “diffusive be on shock accelerated the acceleration”). presence upcross This of to the mechanism a shock, relativistic hydrodynamical energy shock isorder transferred moving in to at the speed particles. The energy gain is proportional to the first PoS(Integral08)020 3 = 05, is a . 1 Φ Θ = Φ J.-C. Leyder ; photon in- (where , in close agree- 2 ]) is not possible ). Moreover, one 2 − ˙ 11 Mv 2.3 cm Θ ]; a high eccentricity 2 1 8 22 powerlaw = erg/s) corresponds to only 10 L ), with a significance larger 34 × 2 found by [ ]. Its mass-loss rate is derived 3 . 10 5 2 s using the parameters adequate 4 − / ' = cm erg H N 22 37 2 corresponds to the 2003 minimum, and 10 10 = × ' Φ 8 2 . L 3 ]. + = 13 3 1 ], and X-ray observations [ H L 7 ]. In addition, two other faint sources are detected N 83, 1.37, and 1.46. No excess was seen at 12 . 0 = erg/s [ 1 keV, column density Φ . 1 5 33 ], infrared [ 6 = 10 1 keV and of . ]. It harbours a Luminous Blue Variable and a less extreme (O- or × 5 kT 9 = kT . It is known to be a binary system, as an orbital period of 5.5 ]), leading to a value of ). Fitting this spectrum with an absorbed and optically thin thermal model / 3 14

]. Three of the observations revealed a high-energy excess (in the 13–20 keV ]. Eta Car has also been classified as a colliding-wind binary, based on its X-ray M 11 3 ; temperature 10 . − 4). 1 . 46). 0 . ]. 1 –10 8 ± 4 1 corresponds to the (spectroscopic) 1998 minimum. As the orbital period is quite long (5.5 years), phases = 1 − mekal 9) has been inferred [ * = . Φ = 0 Φ A spectrum of Eta Carinae could also be extracted, showing that the source is detected up to The total power in stellar wind interactions can be evaluated as There are four BeppoSAX observations of the region, performed with the non-imaging This is thus the very first detection of high-energy non-thermal emission from a colliding-wind The current set of INTEGRAL data covers mostly 3 major periods of observations, summa- Eta Carinae is mostly known for its “Great eruption” in 1843 [ Using INTEGRAL observations, images of the Carina region were built in different energy Γ 1 ' wabs e geometrical factor; [ for Eta Car. This means that the luminosity observed for Eta Car ( greater than 1 are used tocorresponds refer to to the the 2009 next minimum. orbital cycle; therefore, 100 keV (see Figure ( within the BeppoSAX/PDS field of viewsource : (IGR the J10447-6027). anomalous X-ray pulsar 1E 1048.1-5937, and a new PDS instrument [ binary. It is very likely due toelectrons inverse accelerated Compton in scattering the of wind UV collision or zone optical [ photons by high-energy rized in Table to be 10 has been detected using optical( [ 2.2 Previous BeppoSAX observations of Eta Car than 7, and a luminosity of 7 ment with the values of without adding another componentdex to account for the high-energy tail ( 0.1% of the total power involved in stellar wind interactions. spectrum [ WR-type) [ energy range), at the orbital phases 2.3 Current INTEGRAL observations of Eta Car bands. Eta Carinae is detected in the 22–100 keV image (see Figure Hard X-ray emission from Eta Carinae & other colliding-wind binaries 2. Hard X-ray emission from Eta Carinae 2.1 A few words on Eta Carinae although this needs confirmation due to possibleof source the confusion BeppoSAX (see observations Section showed aing high-energy to tail up to 50 keV (in June 2000, correspond- PoS(Integral08)020 J.-C. Leyder 100 1 keV) that does not . 5 = kT 285:59:59.1 ; temperature 286:59:59.1 WR 25 mekal * 4

channel energy (keV) Eta Car 10 PDS FOV wabs 287:59:59.1 IGR J10447-6027 1E 1048.1-5937 288:59:59.1 0:00:00.0 -1:00:00.0 -2:00:00.0 2 2.5 3 3.5 4 4.5

2 5 20 50

10 0.01 10 10 10

−3 −4 −5 −6

keV/cm s keV s 2 Spectrum of Eta Car, combining BeppoSAX and INTEGRAL data (in red). The green fit is INTEGRAL image of the Carina region (22–100 keV; effective exposure time of 1.3 Ms). Three Figure 3: an absorbed and optically thin thermal model ( reproduce the high-energy tail, hence the need for an additional component. Figure 2: sources are detected within the6027. BeppoSAX/PDS field (Note that of WR view : 25outside has Eta of been the Car, ruled INTEGRAL 1E out error 1048.1-5937 as circle and a for IGR all possible J10447- energy counter-part bands of studied.) Eta Car, as it consistently remains Hard X-ray emission from Eta Carinae & other colliding-wind binaries PoS(Integral08)020 4 / 3 ≈ 3 months, an ≈ J.-C. Leyder Car. The orbital Car has been con- 2.5 η η Carinae 637 in the 2–10 keV band (e.g. η 1 yr, followed by a rapid drop to RXTE 1), the emitted X-ray flux ≈ = Φ 2.0 Car is in fact a binary, and then to determine . Its general shape is well explained η 4 Small scale quasi-periodic outbursts in the X-ray Investigations over the last few years have already Car cover mostly three epochs. The corresponding lightcurve have also been detected (Corcoran et al. 1997). of the proposedimum 5.5 was yr successfully orbitalof predicted period. the from The WWC numerical dropobserved. (Pittard models to et min- al. 1998) before being actually et al. 1995; Weischaracteristics et from single al. stars, 2001), which are inmuch typically contrast softer, less to absorbed, theconstant substantially emission in intensity. weaker Since and 1996tinuously Feb monitored relatively by Corcoran et al. 2001a). The lightcurvemarkable (Fig. detail 1) showing a contains re- slow, almostimum linear, over rise a to period max- approximately of 1/6 of the peakalmost intensity for as sharp risetensity to level, approximately and 1/2 then of almost the constant peak intensity for in- parameters, although uncertain, indicatean early-type the companion presence star, which of erful will stellar also wind. have In a suchgas pow- binaries, with a temperatures region of in hotwhere excess shocked of the 10 stellar million KCherepashchuk winds is 1976). collide created The (Prilutskiiregion & wind-wind is Usov expected collision to 1976; (WWC) from contribute this to the system, observedlengths. particularly emission at Previous X-ray X-raysoft and emission observations radio from revealed the wave- nebulasorbed, extended and and strong, variable emission hard, closest highly to ab- the star (Corcoran doubt that the influence of the companion on the system. helped to form a basic picture of η Car Exposure time Significance 1.5 5 Orbital Phase η of Φ ] is shown in Figure ], with a CWB simulation (dotted line). The vertical red bands 15 15 1.0 public data available for Car to understand some η Increase in column density Decrease in plasma emission PCU2 L1 net counts Colliding wind lightcurve (Pittard et al. 1998) Colliding-wind binary ! ! 3), 1 Ms of INTEGRAL observations will be dedicated to the Carina region, = INTEGRAL Φ Car observed with the RXTE satellite and phased to the 5.5 yr orbital period. Plotted are counts detected 123 76–88 192–209 322–330 1.99–2.01 2.16–2.19 2.35–2.37 122 ks 717 ks 180 ks — 6.2 3.3 η 5 J. M. Pittard and M. F. Corcoran: In hot pursuit of the hidden companion of 15 10 25 20 30 Period Rev. Phase

All data 1113 ks 7.3

Net PCU2 L1 counts s counts L1 PCU2 Net erently than single LBVs?). So while the -1 ff X-ray lightcurve of Eta Car [ The main The X-ray lightcurve of Eta Car [ Lightcurve of An important question is the degree to which binarity Figure 4: correspond to the three major periods of observations with INTEGRAL. revolution numbers, orbital phase, effectivethe exposure 22–100 time keV energy and range) significance are of given the for each detection period, of as Eta well Car as for (in the whole data set. Table 1: Hard X-ray emission from Eta Carinae & other colliding-wind binaries by a CWB scenario :or during less) constant of X-ray the flux. ,increases, the When wind as approaching collision periastron the leads (i.e. to twointo the at stars emission the are of huge a getting wind (more closerobserved of in to the the each primary, X-ray other. flux. henceflux the comes Finally, back Then as increase to the the its of two previous secondary the value.the components previous moves However, column get periastron although passages deeper Eta further density in Car away 1998 has explains and from beento 2003, the widely periastron, increase and observed although sharply, drop the during the the extremely column high density has levelobserved. been necessary found to Therefore, explain it the is low believed X-raythe that, flux plasma has in emission never addition been measure to is the alsoof change needed the of (such shock, column as or density, the a one even decrease its thatquestion of would disappearance) can result to be from fully probed a reproduce with modification the INTEGRALthe shape column observations of taken density the at would X-ray not periastron, lightcurve. affect asgeometry the a and/or This flux simple its observed disappearance increase in would of hard clearlyJanuary X-rays, be 2009 while noticed. (at a During change the of next theand periastron shock will passage very in likely lead to new constraints on the behaviour of the shock at periastron. high mass-loss rates, we first need to determine beyond all of the defining LBV characteristics such as their extremely ries evolve di presence of asure companion the can mass bebinary of exploited LBVs such to and stars, help singlejects. we Therefore, LBVs mea- must in may order bear be to in use quite mind distinct that ob- bility that binarity plays aobserved fundamental LBV role outburst in explaining propertiesered (Gallagher has 1989), also thoughbinaries. been most Clearly, consid- LBVs determining are the noterties known wind of and LBV stellardiscussions stars prop- in is Leitherer paramount et al. (see, 1994; for Nota example, et al. the 1996). influences the properties of LBVs (i.e. do LBVs in bina- (e.g. Stothers &like Chin instabilities. The 1993), latter orment could in presuppose arise opacity from - as(e.g. an the Lamers enhance- star 1997), or movesLanger from to 1997; the lower Zethson et influence temperatures al. of 1999). rotation Alternatively, the (e.g. possi- during which a(e.g. transition Langer into a etto Wolf-Rayet al. their star 1994; rarity occurs and Maedernately complex & still nature Meynet have however,ing 2001). no we the unfortu- LBV Due definitive stage. theory Theto majority for drive of LBV proposed mass-loss mechanisms rates instabilities, dur- the and onset underlyingimportance of eruptions, of higher are radiation mass-loss concernedlope pressure of with within the the thestabilities LBV, outer (e.g. and Guzik enve- for et example al. utilize 1999), dynamical pulsational instabilities in- position angle of theremain stars in through the periastron denser passage wind skews of the the shock primary cone until which causes later the phases, line increasingregarded of the as sight absorption in a at fully key these 3D phase times models in (Pittard to the 2000). evolution of massive stars, Fig. 1. in layer 1 ofmodel of the the second wind-wind proportionalin collision. good counter The agreement, unit two agree but (PCU2) well, this and particularly is a the thought duration predicted to of be lightcurve the due (Pittard minimum. to et The the al. rise limitations from 1998) of minimum from modelling is a not the numerical wind collision in 2D. The rapid change in PoS(Integral08)020 J.-C. Leyder 8) is currently being performed. < V 6 ), which is likely to indicate that WR 115 is a binary : indeed, 5 XMM image of WR 115 (shown in the white circle). The blue circle indicates the ISGRI error The variability of the hard X-ray flux observed from Eta Car will be tested by INTEGRAL This research has made use of the SIMBAD database (CDS), of public data from INTEGRAL A systematic search for the hard X-ray emission from Wolf-Rayet stars, non-thermal radio Following the detection of Eta Car, a search for hard X-ray emission from other colliding- ]. However, another strong X-ray source, previously unknown, lays inside the error box of the 16 observations in early 2009, thusthis allowing CWB to at test periastron. the physical models describing the behaviourAcknowledgments of (ESA) & BeppoSAX (ASI). J.-C.L. and G.R.PRODEX acknowledge project. support through the XMM-INTEGRAL 4. Future prospects emitting early-type stars, and O-type stars (with a magnitude Figure 5: box. no single WR star[ from the WN subtypeINTEGRAL has detection, been and unambiguously is detected likelyconclusive so proof to far of be in the the hard the counter-part X-ray X-rays date. of emission from the a hard CWB X-ray other emission. than Eta Thus, Car has no been observed to wind binaries was initiated; ato few date candidates is will the be Wolf-Rayet star investigated.WN6, WR The and 115. most provide New promising evidence optical candidate for observationsof the confirmed absorption presence its lines). spectral of The type an XMM-Newton to OBtion observation be that companion of was (as the recently suggested WR performed by star led the to (see presence the Figure detec- Hard X-ray emission from Eta Carinae & other colliding-wind binaries 3. INTEGRAL observations of other colliding-wind binaries PoS(Integral08)020 562 ]. (June, , MNRAS (Mar., J.-C. Leyder 388 , ApJ Revista Car revealed (Jan., 2008) ]. 399 η 477 Carinae ]. (Apr., 2005) , A&A η Carinae ]. (Jan., 2005) 685–704. Carinae: Binarity , A&A η 129 η (Feb., 1978) 443–455. , A&A (Jan., 1978) 147–156. 429 An XMM-Newton look at the , AJ 182 182 (Apr., 1949) 1169–1174. Detection of a Hot Binary , A&A Carinae 75 η Revista Mexicana de Astronomia y ]. , MNRAS , in , MNRAS arXiv:astro-ph/0510581 ]. The 2003 shell event in , pp. 1–+, June, 1995. The high energy X-ray tail of -ray emission models of the colliding-wind γ arXiv:astro-ph/0603787 ]. ]. Physical Review (Feb., 2002) 636–647, arXiv:astro-ph/0402329 , 7 arXiv:astro-ph/9912387 383 Carinae: Variations on a Theme Hard X-ray emission from η , A&A (Nov., 2005) L37–L40, [ Radio, X-ray, and ]. In hot pursuit of the hidden companion of eta Carinae: An X-ray 633 -ray emission from Wolf-Rayet binaries The dominant X-ray wind in massive star binaries (V. Niemela, N. Morrell, and A. 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