The BeppoSAX High Energy Large Area Survey. IV. On the soft

We present a comprehensive study of the soft X-ray properties of the BeppoSAX High-Energy Large Area Survey (HELLAS) sources. A large fraction (about 2/3) of the hard X-ray selected sources is detected by ROSAT. The soft X-ray colors for many of these obje

Astronomy&Astrophysicsmanuscriptno.(willbeinsertedbyhandlater)

TheBeppoSAXHighEnergyLargeAreaSurvey.

IV.OnthesoftX–raypropertiesofthehardX–ray-selectedHELLASsources

arXiv:astro-ph/0102428v1 24 Feb 2001

C.Vignali1,2,http://doc.guandang.netastri2,F.Fiore3,4,http://doc.guandang.netFranca5

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DipartimentodiAstronomia,Universit`adiBologna,ViaRanzani1,I–40127Bologna,ItalyOsservatorioAstronomicodiBologna,ViaRanzani1,I–40127Bologna,ItalyOsservatorioAstronomicodiRoma,ViaFrascati33,I–00044Monteporzio,ItalyBeppoSAXScienceDataCenter,ViaCorcolle19,I–00131Roma,Italy

DipartimentodiFisica,Universit`adegliStudi“RomaTre”,ViadellaVascaNavale84,I–00146Roma,Italy

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Abstract.WepresentacomprehensivestudyofthesoftX–raypropertiesoftheBeppoSAXHigh-EnergyLargeAreaSurvey(HELLAS)sources.Alargefraction(about2/3)ofthehardX–rayselectedsourcesisdetectedbyROSAT.ThesoftX–raycolorsformanyoftheseobjects,alongwiththe0.5–2keV uxupperlimitsforthoseundetectedintheROSATband,doimplythepresenceofabsorption.ThecomparisonwiththeROSATDeepSurveysourcesindicatesthatalargerfractionofabsorbedobjectsamongtheHELLASsourcesispresent,inagreementwiththeirhardX–rayselectionandthepredictionsoftheX–raybackgroundsynthesismodels.Anotherstrikingresultisthepresenceofasoft(additional)X–raycomponentinasigni cantfractionofabsorbedobjects.

Keywords.Surveys–Galaxies:active–Galaxies:nuclei–Galaxies:starburstX–rays:galaxies

1.Introduction

Whilearelevantfraction(about70–80%)ofthesoftX–raybackground(hereafterXRB)hasbeenresolvedintodiscretesourcesbytheROSATsatellite(Hasingeretal.1993,1998),mostofwhichbeingbroad-lineac-tivegalacticnuclei(AGNs)(Shanksetal.1991;Boyleetal.1994;Schmidtetal.1998;Lehmannetal.2000),inthehardband,wherethebulkoftheenergydensityresides,thenatureofthesourcesoftheXRBisfarlessobvious.Beforetheadventoftheimaginginstrumentson-boardASCAandBeppoSAX,surveysinthehardenergyrangehavebeenperformedwithlimited-spatialresolu-tioninstruments,thusallowingtheidenti cationoftheX–raybrightestsources,whichaccountforasmallfrac-tion(about3–5%,Piccinottietal.1982)ofthehardXRB.TheAGNsobservedathighenergiesbyHEAO1,EXOSATandGingahavespectramuchsteeper(withaphotonin-dexΓ 1.7–1.9)thantheslopeoftheXRBinthesameenergyrange(Γ 1.4–1.5,Gendreauetal.1995;Vecchiet

We present a comprehensive study of the soft X-ray properties of the BeppoSAX High-Energy Large Area Survey (HELLAS) sources. A large fraction (about 2/3) of the hard X-ray selected sources is detected by ROSAT. The soft X-ray colors for many of these obje

2C.Vignalietal.:SoftX–raypropertiesoftheHELLASsources

archiveforcomplementaryX–raydatatothepresenthardX–rayselectedsample.Generally,softX–raycom-ponentsinadditiontothestandardAGNsspectralmod-elsareeitherexcludedfromtheXRBsynthesismodels(http://doc.guandang.netastrietal.1995)or,ifincluded,theydoaccountforasmall,energeticallynotrelevantfractionoftheXRB(Gillietal.1999).Indeed,thereisincreasingevidencethatthebroad-bandspectralpropertiesofthesourcesrespon-sibleforthehardXRBarecharacterizedbymorecomplexspectrathanisexpectedfromasimpleabsorbedpower-lawmodel(DellaCecaetal.1999;Giommietal.2000),ascon rmedbythepresenceofmulti-componentsspectrainobscurednearbyAGNs(Awakietal.2000).Thepossibil-ityoftheexistenceofsuchadditionalcomponentsmustbetakenintoaccountwhencomparingsurveysperformedindi erentenergyrangesand,mostimportant,atlimiting uxesdi eringbyone(ormore)orderofmagnitude.

2.Thesample

2.1.TheHELLAShardX–ray-selectedsample

142highGalacticlatitude(|b|>20 )MECS eldscoveringabout80squaredegreesofskyhavebeenanalyzed.Ade-taileddescriptionofBeppoSAXinstrumentalcapabilities,sourcedetectionalgorithmsandphotonstatisticsisde-scribedbyFioreetal.(2001,paperII).Forthepurposesofthepresentpaper,wehaveconsideredthefulllistof147BeppoSAXsourcesdetecteddowntoa uxlimitofabout5×10 14ergcm 2s 1.

2.2.TheHELLASsourcesinROSATarchivaldata

TheBeppoSAXcataloguewascross-correlatedwitharchivalROSATdata(PSPC,HRIandRASS).108outofthe147sourcesareinROSAT elds;foronly1sourceRASSdatahavebeenused,duetothelackofpointedROSATobservations.4sourceslyingbeneaththePSPCdetectorwindowsupportstructurewillnotbeconsideredinthefollowingdiscussions,thereforetheusefulnumberofHELLASsourcesinROSAT eldsis104.InthosecaseswheremultipleobservationsofthesameHELLASsourcearepresent,wechosetheonewiththelongestexposuretimeand/orthelowesto -axisangle(andcheckedtheresultsbyanalyzingatleastanotherimageofthesame eld).

3.ROSAT elds

3.1.ROSATsourcedetection

TheROSATdatahavebeenanalyzedwiththeMIDAS/EXSASpackage(Zimmermannetal.1998).Thesourceshavebeendetectedbyrunningthelocalde-tectionalgorithmLDETECT,thebicubicspline ttothebackgroundmapandthemapdetectionalgorithmMDETECT.ThedetectionthresholdofthesealgorithmswassetatalikelihoodofL= ln(Pe)=10,corresponding

toaprobabilityoftheorderof4.5×10 5thattheobservednumberofphotonsinthesourcecellisproducedbyapurebackground uctuation(about4σdetection,Cruddaceetal.1988).ThemeasuredcountswerethencorrectedforPSPCvignettingandthesourceparametersweredeter-minedbythemaximumlikelihoodmethod(MAXLIK).ThesourceswhichpartiallyfellunderthePSPCwindowsupportstructureandwhichweremissedbythedetec-tionroutinehavealsobeenanalyzed,andthevignetting-correctedcountrateshavebeenobtainedinthedi erentenergybands.Eventhoughtheabovedescribedroutineshavebeenextensivelyappliedinthepast,wehavefurthercheckedthereliabilityofallthedetectionsbyrunningtheslide-celldetectionalgorithminXIMAGE(Giommietal.1991)inasimilarwaytothatdescribedinFioreetal.(2000a)forallthesourcesofthepresentsample,obtainingsimilarresultswithintheerrors.Mostofthesourcesareal …… 此处隐藏：33846字，全部文档内容请下载后查看。喜欢就下载吧 ……