Produit, N

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29th International Cosmic Ray Conference Pune (2005) 4, 259262Main results from the INTEGRAL missionN. Produit on behalf of the INTEGRAL science working team(a) ISDC, Universit·e de Geneve, SwitzerlandPresenter: N. Produit (Nicolas.Produit@obs.unige.ch), swi-produit-N-abs1-og22-oralINTEGRAL is an European Space Agency (ESA) astronomical satellite for observing the gamma-ray sky in thekeV to MeV energy range. Highlights of the main results obtained since the start of the mission are presented.1. IntroductionINTEGRAL[1], the ESA gamma-ray observatory, was launched on October 17, 2002. Since this date, it tookdata of excellent quality while experiencing no major flaw.The instruments on board INTEGRAL are sensitive to  -rays from 2 keV to 1 MeV. They can all provideimages and spectra but some of them are specialized in just one of these two tasks. The imager IBIS[2] hasa field of view of 19  by 19  for a point source location accuracy of 1-2 arcmin. The spectrometer SPI[3]has a sensitivity for narrow lines of 2.5 10  ph cm  s 	 and a spectral resolution of 3 keV. The two JEMXmonitors[4] are specialized for photons in the X-ray domain and cover an energy range from 2 to 20 keV.INTEGRAL is an observatory-type mission. Most of the total observing time (70%) is awarded as the GeneralProgram to the scientific community at large. The rest of the time (Core Program) is devoted to periodicGalactic surveys, deep Galactic center exposures, and targets of opportunities. All the data become public afterone year. More then one year of data is already publicly available for download on the INTEGRAL sciencedata center (ISDC) web site[5].2. CatalogsOne year’s worth of all Core Program exposures (5 Msec) were mosaicked to produce a deep all-sky map. Thismap was searched for known and new sources and a catalog was published[6]. The maps are not homogeneousin depth everywhere (see figure 1), as most of the Core Program time is devoted to the Galactic disk and center.Yet, a typical position accuracy of 0.72 arcmin and a sensitivity of 1 mCrab are achieved almost everywhere.On hundred and twenty-three sources are found in this catalog: 5 Active galactic Nuclei (AGN), 5 whitedwarfs, 4 radio pulsars, 3 supernova remnants (SNR), 54 low mass X-ray binaries (LMXB), 24 high massX-ray binaries (HMXB), and 28 unidentified sources.This catalog activity will continue and eventually use all the public data. The map will become deeper andmore complete, and as the  -ray sky is highly variable, we will continue to serendipitously discover moresources. Follow-up observations in other wavelengths are needed to understand the nature of the unidentifiedsources.3. Compact sources account for all the soft  -ray emission of the GalaxyThanks to the high spatial resolution of the imager, most of the total emission of the Galaxy from 2 keV to120 keV can be assigned to visible point sources[7]. In fact, in the band 40 keV to 120 keV, there is no indica-tion of an interstellar emission. In the 20 keV to 40 keV band, a Galactic diffuse component can contribute atmost 13% of the total emission.This means that the situation in the soft  -ray domain is very different than in the X-ray domain (  10 keV)260 N. ProduitFigure 1. INTEGRAL exposure map of all public data on 15 April 2005where a diffuse component dominate. This also means that the emission mechanism changes drastically be-tween 10 and 20 keV.This measurement places strong constraints on the population of GeV cosmic-ray electrons that would con-tribute to the diffuse background by inverse Compton scattering, and on the population of lower energy elec-trons that would radiate through bremsstrahlung on interstellar gas.4. IGR sourcesOn January 29, 2003, only three months after the launch, INTEGRAL found its first new uncatalogued high-energy source IGR J16318-4848[8]. Today (June 2005), the number of IGR sources amounts to 55 (for an upto date list see [5]). Follow-up observations of IGR J16318-4848 at other wavelengths have shown that thissource is likely to be a high mass X-ray binary (HMXB).All the new sources are located very near to the Galactic disk and predominantly in regions with high OB starformation rate. It is therefore likely that most of them are HMXB. The sources that have been followed withthe Chandra and XMM satellites show strong absorption, explaining why they were discovered first in  -raysrather then in X-rays. All sources are strongly variables.It seems that all these new sources constitute a new population of HMXB[9].5. Center of the GalaxyUsing a 1 Msec observation of the Galactic center[10], a deep map of the vicinity of Sgr A* was produced.In the central 2  x2  field, 5 known sources are clearly seen: 1E 1740.9-2942.7, KS 1741-293, A 1742-294,1E 1743.1-2843, SLX 1744-299/300 and a new uncatalogued source IGR J1745.6-2901. The flux of this newsource varies with time. The position is compatible with the Sgr A* radio position and incompatible withthe the position of GRS 1741.9-2853 which is not detected in this sample. All these hints seem to indicatethat IGR J1745.6-2901 is the  -ray counterpart of the Galactic nucleus. The flux in the 20 to 40 keV band is1.92  0.36 10 	 erg cm  s 	 , and 1.86  0.40 10  erg cm  s 	 in the 40 to 100 keV band, making it aMain results from the INTEGRAL mission 261faint, but by far not the faintest, source discovered by INTEGRAL.If our super massive black hole seems to be very quiet right now, it was perhaps not the case in the past. Wehave now the intriguing possibility to prove this. The radiation emitted in the past by Sgr A* could be Comptonscattered and reprocessed by giant molecular clouds and delayed by the light travel time. In that case, the sourcemust be weak in X-rays but strong above 15 keV making it ideal for INTEGRAL. Revnivtsev et al[11] haveshown that we are seeing a 300-year delayed signal of Sgr A* as a reflection on the giant molecular cloudSgr B2. This analysis shows that, 300 years ago, Sgr A* was a few 10  times more luminous in  -rays than itis now. This high luminosity of Sgr A* must have lasted for at least 10 years as proven by historical data of theluminosity of Sgr B2. Models based on cosmic-ray heating of Sgr B2 are rebuked as they cannot explain at thesame time the X-ray and the  -ray spectra of Sgr B2.6. Emission linesThe center of our Galaxy is a known strong source of electron-positron 511 keV annihilation radiation.Kno¨dlseder et al[12] have shown that the annihilation signal is coming from the bulge. The source shape isincompatible with a single point source. There seems to be no disk component[13].Aluminum-26 nucleosynthesis is common throughout the Galaxy. There are suggestions that it is primarilycreated by massive stars. This isotope  -decays with a half-life of 1.04 10  years and emits a 1808.7 keVphoton. Using data of the first year, R. Diehl et al[14] have clearly detected the signal of  Al but more data isstill needed to compete with previous results of COMPTEL.7. Anomalous X-ray Pulsars (AXP)AXP are isolated neutron stars with very high magnetic fields 10  to 10  G. Their rotation period is around10 s. The derivative of their period is large (10 	 s/s) and steady. Their X-ray luminosity cannot be explainedjust by their rotational energy loss.Out of 6 known AXP in the Galaxy, INTEGRAL has found hard spectral tails in 4 of them (1E1841-045[15];1RXS J1708-4009; 4U0142+614; 1E2259+586). The tails are pulsed and no spectral break is seen up to thehighest reachable energy. This comes as a surprise as it was not predicted by current AXP models that considerthem as soft spectrum objects.8. HESS counterpartsVery early in the mission, 4 HESS/IBIS associations (Crab, Sgr A*, PSR B1509-58 and AX J1838.0-0655)were already observed.The HESS collaboration recently published[17] the discovery of 8 new sources seen in  -rays  200GeV.INTEGRAL has discovered 2 new HESS/IBIS associations among the 8 new sources: The new INTEGRAL point-like source IGR J18135-1751[16] has a powerlaw emission from 1 to 100keV and is spatially compatible with HESS J1813-178. Its radio counterpart is a shell type supernovaremnant.262 N. Produit AX J1838.0-0655, one of the unidentified objects listed in the first IBIS/ISGRI survey catalog, locatedin the Scutum arm region is the likely counterpart of the TeV source HESS J1837-069. In the INTE-GRAL data, this source is persistent, has a powerlaw (  =1.66  0.23) spectrum and a 20-100 keV flux of4.2 10 	 erg cm  s  [18]. X-ray data show an absorption which is a factor of 2 to 3 in excess of theGalactic value and they show a point-like morphology. The source is probably a shell type or a plerionicsupernova remnant.More data is being collected to follow-up the other 6 HESS sources.9. ConclusionsWe were not able to speak about many other very interesting science done with INTEGRAL such as thediscovery of the fastest spinning accreting neutron star[19], GRBs, High mass X-ray binaries, micro-quasarsor AGN.INTEGRAL has already been a very fruitful mission. It discovered a new class of sources and it advanced ourknowledge of the  -ray sky. We know now that the super massive black hole at the center of our Galaxy wasnot always as quiet as we see it today.Most of the published results make use of just the first year of data. As more data are becoming publiclyavailable every month, and as the analysis software released by ISDC (version 5 in August, 2005) is improving,we expect more exiting results from INTEGRAL in the near future.References[1] Winkler, C., et al., 2003 A&A, 411, L1[2] Ubertini, P. et al., 2003 A&A, 411, L131[3] Vedrenne G. et al, 2003 A&A, 411, L63[4] Lund, N et al, 2003 A&A, 411, L231[5] http://isdc.unige.ch[6] Bird, A.J. et al. 2004, Ap.J.,607L, 33B[7] F. Lebrun et al., Nature 428, 293, 2004[8] Walter, R. et al, 2003 A&A, 411, L427[9] Walter, R. et al. A&A subm., 2005[10] Belanger, G. et al. ApJ, Vol. 601, L163-L166 2004[11] Revnivtsev, M. et al., A&A 425, L49, 2004[12] Kno¨dlseder, J. et al., A&A 411, L457, 2003[13] Teegarden et al.,APJ 621 296-300, 2005[14] Diehl, R. et al., A&A 411, L451, 2003[15] Kuiper, L. et al. APJ. 613, 1173-1178, 2004[16] Ubertini, P. et al, astro-ph/0505191 to appear in ApJ Letters[17] Aharonian, F. et al. 2005, Science, 307, 1938[18] Malizia, A. et al. 2005, submitted to Ap. J.[19] Shaw et al., A&A Letters 432, 13, 2005

Main results from the INTEGRAL mission

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