Revealing the nature of the highly obscured galactic source IGR J16318-4848

The X-ray source IGR J16318-4848 was the first source discovered by INTEGRAL on 2003, January 29. We carried out optical and near-infrared (NIR) observations at the European Southern Observatory (ESO La Silla) in the course of a Target of Opportunity (ToO)

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aToappearin“CompactBinariesintheGalaxyandbeyond(2003)”RevMexAA(SC)REVEALINGTHENATUREOFTHEHIGHLYOBSCUREDGALACTICSOURCEIGRJ16318 48480S.Chaty,1,2,4andP.Filliatre2,3RESUMENElresumenser´atraducidoalespa nolporloseditores.TheX-raysourceIGRJ16318 4848wasthe rstsourcediscoveredbyINTEGRALon2003,January29.Wecarriedoutopticalandnear-infrared(NIR)observationsattheEuropeanSouthernObservatory(ESOLaSilla)inthecourseofaTargetofOpportunity(ToO)programme.Wediscoveredtheopticalcounterpartandcon rmedanalreadyproposedNIRcandidate.NIRspectroscopyrevealedalargeamountofemissionlines,includingforbiddenironlinesandP-Cygnipro les.Thespectralenergydistributionofthesourcepointstowardsahighluminosityandahightemperature,withanabsorptiongreaterthantheinterstellarabsorption,buttwoordersofmagnitudelowerthantheX-rayabsorption.WeshowthatthesourceisanHighMassX-raybinary(HMXB)atadistancebetween~1and~6kpc,themassdonorbeinganearly-typestar,probablyasgB[e]star,surroundedbyarichandabsorbingcircumstellarmaterial.ThiswouldmakethesecondHighMassX-rayBinary(HMXB)withasgB[e]starafterCICam,indicatingthatanewclassofstronglyabsorbedX-raybinariesisbeingunveiledbyINTEGRAL.ABSTRACTTheX-raysourceIGRJ16318 4848wasthe rstsourcediscoveredbyINTEGRALon2003,January29.Wecarriedoutopticalandnear-infrared(NIR)observationsattheEuropeanSouthernObservatory(ESOLaSilla)inthecourseofaTargetofOpportunity(ToO)programme.Wediscoveredtheopticalcounterpartandcon rmedanalreadyproposedNIRcandidate.NIRspectroscopyrevealedalargeamountofemissionlines,includingforbiddenironlinesandP-Cygnipro les.Thespectralenergydistributionofthesourcepointstowardsahighluminosityandahightemperature,withanabsorptiongreaterthantheinterstellarabsorption,buttwoordersofmagnitudelowerthantheX-rayabsorption.WeshowthatthesourceisanHighMassX-raybinary(HMXB)atadistancebetween~1and~6kpc,themassdonorbeinganearly-typestar,probablyasgB[e]star,surroundedbyarichandabsorbingcircumstellarmaterial.ThiswouldmakethesecondHighMassX-rayBinary(HMXB)withasgB[e]starafterCICam,indicatingthatanewclassofstronglyabsorbedX-raybinariesisbeingunveiledbyINTEGRAL.KeyWords:STARS:CIRCUMSTELLARMATTER—STARS:EMISSION-LINE—BE—X-RAYS:BI-NARIES—IGRJ16318-4848IGRJ16318 4848hasbeenthe rstsourcetobediscoveredbytheINTEGRALimagerIBIS/ISGRI

on2003January29,0.5 southfromthegalac-ticequator(Courvoisieretal.2003).Asubse-quentobservationbyXMM-Newtonon2003Febru-ary10localizeditwithanaccuracyof4′′,thehighenergyspectrumsuggestingahighcolumnden-sityofNH>1024cm 2(Matt&Guainazzi(2003),Walteretal.(2003)).InthecourseofaToOpro-grammeatESOtolookforcounterpartsofhighen-ergysourcesdiscoveredbysatellitesincludingIN-

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