SRGA J124404.1–632232 SRGU J124403.8–632231 New X-ray pulsar discovered in the all-sky survey by the SRG 2022 V. Doroshenko.pdf

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©ESO2022Astrophysics
TheEarlyDataReleaseofeROSITAandMikhailPavlinskyART-XContheSRGmissionSpecialissue
−632232/−632231:NewX-ray
pulsardiscoveredintheall-skysurveybytheSRG
,,,,,,,,
,6,,,,,
,9,,6
1InstitutfürAstronomieundAstrophysik,Sand1,72076Tübingen,Germany
e-mail:******@-
2Max-Planck-InstitutfürextraterrestrischePhysik,Gießenbachstraße1,85748Garching,Germany
3Leibniz-InstitutfürAstrophysikPotsdam(AIP),AnderSternwarte16,14482Potsdam,Germany
-SternwarteandErlangenCentreforAstroparticlePhysics,Friedrich-Alexander-UniversitätErlangen-Nürnberg,
,96049Bamberg,Germany
5SouthAfricanAstronomicalObservatory,POBox9,ObservatoryRd,Observatory7935,SouthAfrica
6DepartmentofAstronomy,UniversityofCapeTown,PrivateBagX3,Ronde***7701,SouthAfrica
7SpaceResearchInstitute(IKI)ofRussianAcademyofSciences,Prosoyuznayaul84/32,117997Moscow,RussianFederation
8AstronomicalObservatory,UniversityofWarsaw,,00-478Warsaw,Poland
9SouthernAfricanLargeTelescope,POBox9,ObservatoryRd,Observatory7935,SouthAfrica
Received21April2021/Accepted13July2021
ABSTRACT
Ongoingall-skysurveysbytheeROSITAandtheMikhailPavlinskyART-XCtelescopesonboardtheSpectrum-Roentgen-
Gamma(SRG)missionhavealreadyrevealedoveramillionofX-,−632232/
−632231,wasdetectedasanewsourceinthethird(oftheplannedeight)consecutiveX-raysurveysbyART-XC.
Basedonthepropertiesoftheidentifiedopticalcounterpart,itwasclassifiedasacandidateX--up
observationsofthissourcewiththeNuclearSpectroscopicTelescopeArray,theNeilGehrelsSwiftObservatory,andtheSouthern
AfricanLargeTelescope,−632231
asanewX-raypulsarwithaspinperiodof∼538sandaBe-starcompanion,makingitoneofthefirstGalacticX-raypulsarsdiscovered
bytheSRG.
:individual:-632232/-632231–stars:neutron–binaries:general
(;).However,asignificant
expansionofthesampleofGalacticX-raybinariescanalsobe
TheSpectrum-Roentgen-Gamma(SRG)missionwaslaunchedanticipatedandwillhelptoobtainimportantconstraintsontheir
onJuly13,2019,fromBaikonurandstartedtheall-skysurveyonluminosityfunction(;Doroshenkoetal.
December12,,eightcompletescansofthecelestial2014).Ofparticularinterestherearethepropertiesofthefaint
sphereofsixmonthseachareforeseentobeconductedwitheachBeX-raybinaries(BeXRBs),whichsofarhavebeenmostlydis-
ofthetwoinstrumentsonboardtheSRG:eROSITA(Merlonicoveredwithall-
;)andMikhailPavlinskyART-XCisquiteclear,however,thatthepopulationofknownBeXRBs
()–10keVbandandispotentiallyonlythetipofanicebergbecauseobjectsexhibit-
the4–
BothinstrumentsproducestandardX-rayeventdataandduetothelowsensitivityofall-skymonitors(Doroshenkoetal.
thereforenotonlyimages,butalsospectraandlightcurves2014).Incomparisonwithavailablewide-fieldinstruments,both
-eROSITAandART-XCaresignificantlymoresensitiveandare
vey,theeROSITAsurveysareexpectedtobeafactor20–
moresensitivethantheROSATAll-SkySurveyinthesamewillthusfacilitateadvancesinourunderstandingoftheorigin
−−−
energyband(∼×1015ergcm2s1foreROSITA(PredehlandevolutionofGalacticX-raybinaries.
−−−
)comparedto∼1013ergcm2s1()On2021January27,duringthethirdconsecutiveall-
forROSAT).Moreover,SRGwillalsoconductfirstevertrueskysurvey,theMikhailPavlinskyART-XCtelescopeon
imagingall--raysource
AlargemajorityoftheseveralmillionsofnewX-−632232withafluxof∼10−11ergcm−2s−1in
detectedinthesurveyareexpectedtobeextragalacticobjectsthe4–12keVenergyband().Inspectionof
(.,activegalacticnucleiandgalaxyclusters)andordinarystarstheART-XCdatafromtheprevioustwosurveysin2020(see
ArticlepublishedbyEDPSciencesA21,page1of7
A&A661,A21(2022)
Table1forasummaryoftheobservations).
thisposition,,
itwasfoundthatanobjectwasdetectedbyeROSITAinallthree
InstrumentT,MJDT,MJDExposure(ks)
-raypositionandidentify-startstop
ingatentativeopticalcounterpartoftheX-raysource(
).Near-infraredandX-raycolors,theX-rayflux,
anestimatedX-rayluminosityof∼1034ergs−
Gaiadistanceof∼(Bailer-)stronglyART-
suggestedthattheobjectmaybeanewhigh-massX-
(HMXB).Thevariabilityofthecounterpart,inparticular,aweakSwift/
periodic,∼138d,opticalfluxvariationsrevealedbytheOpti-
calGravitationalLensingExperiment(OGLE,Mroz&Udalski
2021)stronglysupportedthissuggestionassimilarvariability
iscommonlyobservedalsoinotherhigh-massX--XCdatamostly
withBe-,wetoimproveconstraintsonthesourcefluxbyeROSITAinthe
observedthecounterpartwiththeSouthernAfricanLargeTele-,weattributedallcountsdetectedby
α
scope(SALT;),revealingaprominentHART-XCtotwobroadenergybinscoveringthe4–12keVband
lineinemission().ThisistypicalforBeandmodeledtheART-
X-raybinariesandalsostronglysupportstheBeXRBnatureofwenotealsothateventhoughART-XCandeROSITAobserved
-upobservationsofthesourceataboutthesametime,thedifferenceinfieldofview
thisX-raysourcewithNuclearSpectroscopicTelescopeArrayofthetwoinstrumentsandthescanningpatternoftheall-sky
NuSTAR
().surveyimplythattheobservationsarenotstrictlysimultaneous.
Weherereportindetailontheanalysisoftheobserva-ThesourcefluxmeasuredbyART-XCwasthereforeestimated
NuSTAR
tionaldataof,SALT,.
,wefirstbrieflydiscusstheobser-InadditiontoSRGdata,adeep(55ks,)
vationsweusedandthendiscusstheanalysisstepsindetailthatobservationofthesourcewithNuSTAR()
ledtotheidentificationofthenear-infraredcounterpartofthewasobtainedtocharacterizethebroadbandspectrumofthe
X---
NuSTAR

findingsinthecontextofthepropertiesofotherBeXRBsin20210210,,theNeilGehrels
(Swift)alsoobservedtheobjectwiththeXRT
telescope(),sothatweusedthisobservation
aswell.
,aspartofatransientidentificationandcharac-
terizationprogrambeingundertakenatSALT(Buckley2015),
Asdescribedabove,therearetwotelescopesonboardSRG,weobservedtheopticalcounterparton2021January29using
eROSITAandART-(RSS)inlow-resolutionmode
etal.(2021)andPavlinskyetal.(2021),(R=420).Inparticular,twospectrawith1ksexposureeachcov-
theexposuresachievedinthesurveysofararecomparatively
low,thedatafrombothinstrumentsweremostlyusedtoobtaineringtheregion3300–9000Åwereobtainedstarting23:34:05
aprecisepositionoftheX-raysourceandmeasurefluxvaria-.
tionsbetweenthethreeconsequentsurveys,whereasNuSTARFinally,tostudythepropertiesoftheopticalcounterpart,we
I
-usedthearchivalOGLE-bandlightcurvepublishedbyMroz
&Udalski(2021).ItisavailablethroughtheOGLEXROM
sideringthenondetectionofthesourcebyART-XCinthefirst1
twosurveys,weonlyuseddatafromthethirdsurveyforthisservice.
,datafromallthreesurveyswereused.
eROSITAdatawereprocessedusingthecurrent(c946)-raypositionandnear-infraredcounterpart
eSASS()pipelineconfiguration(usedto
TodeterminetheX-raypositionofthesource,weconsideredthe
characterizethesoftwareandcalibrationfileversion),whichwas
rectifiedsourcepositionsfromthreeeROSITAsurveysasinde-
alsousedtoderivethesourcepositionandtoextractX-rayspec-
pendentmeasurementsandcombinedthemfollowingtheproce-
trathatweremodeledjointlywithNuSTARdatatoimprovethe
duredescribedinDoroshenkoetal.(2020).Thisallowedusto
low-
fixthefinalX-=,=−
Detailsoncalibrationandin-orbitbackgroundofeROSITAare◦0000000
∼
reportedinDennerletal.(2020)andFreybergetal.(2020),
a3σconfidencelevel(notaccountingforpotentialsystematic
-skysurveyswereana-00
uncertainties(upto5)ofindividualeROSITAmeasurements).
lyzedindependently,althoughthespectrumofthesourcewas
-raypositioncoincideswiththe
assumedtobethesameinallofthem,asdescribedbelow.
near-infraredsource2MASSJ12440380−6322320,whichwas
ART-XCdatawereprocessedwiththeanalysissoftware
thussuggestedasthetentativeopticalcounterpartoftheX-ray
.
source().Consideringthevariabilityreported
AdescriptionoftheART-XCtelescopeandtheanalysissoft-
byMroz&Udalski(2021),weobservedtheobjectwithSALT
warecanbefoundinPavlinskyetal.(2021).Becausethesource
()tofinallyconfirmthisidentification.
isfaintandtheeffectiveexposureforART-XCissignificantly
shorterasaresultofitssmallerfieldofview,itwasonlypos-1.
sibletodetectthesourceandestimatethenumberofcounts1-
A21,page2of7
.:NewX-−632232/−632231
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12:44:

10912286348246895885709282889483106901188613081

1
−
˚
A
,
1
−

2
−


15
−inthe3–
−
regionsarealsoshown(greencircles).

Flux,10
−±Å±Å,
−5Å,although
λ
,A˚thisishardtomeasurepreciselybecauseattheblueendofthe
spectrum,thesignal-to-noiseratio(S/N)
:VVV(JHKS)imageoftheregionaroundthe
X--
byeROSITAineRASS1-3,theredcontoursrepresentthe1σand3σposedorbitalperiodof138days(Mroz&Udalski2021)andthe
-knowncorrelationbetweenorbitalperiodandHαEWin
The2MASSpositionofthesuggestednear-infraredcounterpartisindi-BeXRBs(Reig2011),theexpectedEWwouldbeabout−35Å,
:spectrumoftheopticalcounterpartthereforeourmeasurementsuggeststhatthediskhasgrownto
asobservedbySALT,
thereforeindeedcanbeexpectedtobeactiveinX-rays.
Inparticular,theproposedopticalcounterpartwasobserved
usingthelow-resolution300lmm−1transmissi