Hydrodynamical simulations of the jet in the symbiotic star(4)

In papers I and II in this series, we presented hydrodynamical simulations of jet models with parameters representative of the symbiotic system MWC 560. These were simulations of a pulsed, initially underdense jet in a high density ambient medium. Since th

4

Fig.2.—X-rayluminosityasafunctionoftheevolutiontimeofrangethei.e.0.15jetin–model15i’(solid)andmodeliv’(dashed)intheenergykeVtheareplotssimilar.

showingkeV.Mosttheluminosityoftheenergyintheisemittedenergyrangebelow0.152keV,–2simulationsasfollows.WeusedtheatomicdatabaseATOMDBwithIDLincludingtheAstrophysicalPlasmaEmissionDatabase(APED)andthespectralmodelsoutput

fromtheAstrophysicalPlasmaEmissionCode(APEC,Smithetal.2001)tocalculatetheemissivity.ThedefaultabundancesinATOMDB,i.e.14elements(H,He,C,N,O,Ne,Mg,Al,Si,S,Ar,Ca,Fe,Ni)withsolarabundancesofAnders&Grevesse(1989),areused.Theenergyrangeisdividedintobinsof0.01keV.Wecomputethespectrumandthetotal uxinX-raysasafunctionofevolutionarytimeforeachofourmodels.WecalculatetheX-rayemissionintherangebetween0.15–15keV,whichisexactlytheenergyrangecoveredbyEPIConXMM-NewtonandincludesthatoftheACISinstrument(0.2–10keV)andofHETG(0.4–10keV)onChandra.Theemissionfromgaswithatemperaturelowerthan 106Kisonlymarginalinthisenergyrange.

3.THETOTALX-RAYLUMINOSITYANDITSTIME

DEPENDENCE

Asexpected,thehightemperatures,createdbythein-teractionofthejetpulseswithpreviouslyejectedmatter,leadtosubstantialX-rayemission(Fig.2).TheX-rayluminosityinmodeliv’ishigherthaninmodeli’.ThisisaresultofthehigherdensityinthepulsesofthehigherkineticluminosityL˙andthus

v2pumpedjet.Furthermore,inmodeljet=1/2M

intothei’about5%oftheaveragekineticluminosityisradiatedinX-rays,butinmodeliv’about19%.SincetheX-raysareemittedbyshockedmaterialfromthefastmovingpulsesandsincetheX-rayluminosityisproportionaltoρ2,comparedtoLjetbeingproportionaltoρ,theratiooftheX-raylu-minositytothekineticluminosityisproportionaltoρ.Thereforethisratioishigherinmodeliv’thaninmodeli’.

We ndminimaandmaximaintheX-rayemissionL(computedbyintegratingovertheenergyrange0.15–15XkeV)whichareconnectedwiththeperiodicemergenceofjetpulses(Fig.3).ThustheperiodofthevariationsintheX-rayemissionisabout7days.Thesizeofthe uctuationsis50%andmoreoftheaverageemission.WhiletheX-rayluminositystaysconstantwithtimeformodeli’,itdecreaseswithtimeformodeliv’.Thisdi erencemightberelatedtoalargeramountofcoolinginmodeliv’.Theinitialshocktemperatureisidenticalinbothmodels,sincethevelocitiesarethesame.The

Fig.3.—X-rayluminosityasafunctionoftimeformodeli’(top)createdandmodeliv’(bottom);onecanindecreasesthetopbyplotstheemergenceshowthedi erentofeachnewtrendsjetseeofpulse;minimatheX-raytheanddottedmaximaluminositylineshigherdensitieswithtime.

inthejetpulsesinmodeliv’,however,leadtohigherdensitiesintheX-rayemittingmaterialandthustohigherpressureswhichresultinstrongeradi-abaticexpansionandhenceenhancedadiabaticcooling.Radiativecoolingisalsoenhancedbythehigherdensitiesinmodeliv’.

4.THESPECTRUMANDITSTIMEDEPENDENCE

Thespectraofbothmodelsintheenergyrangebe-tween0.15–15keVshowmanydi erentfeatures.Theyshowcontinuumemission,andsuperimposedonthecon-tinuum,alargenumberofemissionfeatures(someofwhichareblendsofseveralemissionlines).Aprominentfeature,whichismainlyduetoblendedironlines,isseenbetween0.7–1keV.Ironalsoproducesastrongemissionfeatureinthe6.4–76.7keVrangerequiringveryhightemperatures(～10K)thatarereachedlocallyinthejet.

LikethetotalX-rayluminosity,thespectrumisalsohighlytime-dependent(Fig.4).Wede netwoproxiesforthetemperature,oneusingthelowenergyspectrumandoneusingthehighenergyspectrum.Theseproxiescanthenbeusedconvenientlyfordirectcomparisonwiththesingle-temperaturethermalplasmamodelstypicallyusedto ttheobserveddata.

4.1.De ningtemperatureproxies

Inordertocharacterizethetemperatureoftheprop-agatingjetfromthelowenergyspectrum,weusethefactthatbelowenergiesofabout0.7keV,bothspectrainFig.4arealmostidentical,butdi ersigni cantlybe-tween0.7and2keV.Thereforewede netheproxyζfor