TheMERGer-eventGamma-Ray(MERGR)Telescope

J.EricGrove,L.J.Mitchell,B.F.Phlips,C.C.Cheung,M.Kerr,R.S.Woolf(NRL)M.S.Briggs(UAH)J.S.Perkins(NASAGSFC)

MERGRisdesignedtodetectandlocalizeGamma-RayBursts(GRBs)– particularlytheshortGRBelectromagneticcounterpartsofgravitationalwavedetectionsofneutron-starbinarymergers.Employingproventechnology,itcanbedeliveredonanaggressivescheduleforlaunchbytheDoDSpaceTestProgramin2021.

DevelopmentofMERGRatNRLissupportedbytheChiefofNavalResearch

MERger-eventGamma-Ray(MERGR)Telescope

Motivationandplan• WiththeannouncementofGW170817,theeraofgravitational

wavedetectionsofneutronstar(NS)binarymergershasbegun.

• MERGRwillworkasastandalonesystemoraspartofanetworkoftelescopes.Itwillincrease𝛾-rayskycoveragetodetecttheshortGRB(SGRB)counterpartsofNS-binarymergers.

• Tominimizecostandtimetofirstlight,MERGRisderiveddirectlyfromtheStrontiumIodideRadiationInstrumentationseries(SIRI-1andSIRI-2)demonstratorsdesignedandbuiltatNRLfortheDoDSpaceTestProgram.

TelescopeDesign• MERGRconsistsof19DetectorAssemblies,eachwitha3.8

cmx1.27cmhexagonalSrI2:Eucrystalreadoutbyahexagonalarrayofsiliconphotomultipliers(SiPMs).

• SrI2:Euhashighdensity(4.2g/cm3),goodstoppingpower,andexcellentenergyresolution.

• Totalmass13kg,andtotalpower21W.

Right:CADrenderingofMERGRfromtheinstrument’szenithshowingthelocationsofthe19hexagonaldetectorsinaclosely-packeddomegeometry.

Left:Off-axisviewshowingMERGR’selectronicsbay.

Grove,MERGR|2

MERger-eventGamma-Ray(MERGR)Telescope

Technology readiness• MERGRinheritsdirectlyfromtwoinstruments,SIRI-1andSIRI-2,thatwedevelopedforDoDSpaceTestProgram(STP)launch.

• SIRI-1willspace-qualifystrontiumiodidescintillatorsandSiPMreadouts.IthasbeendeliveredtothespacecraftvendorandisscheduledforlaunchintoLEOonSTPSat-5.

• SIRI-2isafollow-ondetectorarrayofsevenSrI2:Eudetectorsforatmosphericburstmonitoring,scheduledtolaunchintoGEOinlate2018onboardSTPSat-6.

• Wehaveproposedtodesign,assemble,andtestMERGRtodeployby2021.TheDoDSTPprovidesalaunchopportunityandfundsforitsintegrationintothespacecraftbus,launchservices,andthefirstyearofexperimentdatacollection.

• UsingexistingalgorithmsdevelopedandtestedatNRL,instrumentflightsoftwarewillprovidereal-timeburstdetectionsandlocations,whichwillbetransmittedtotheGamma-rayCoordinatesNetworkforworldwidedistribution.

Grove,MERGR|3

SrI2:EudetectorsdevelopedforuseonSIRI-2.MERGRdetectorswouldbeidentical,expectforthickness.(Top)ExplodedCADrenderingofdetectorassembly.(Bottomleft)19-elementSiPM arraydevelopedbyNRLforreadoutofhexagonalcrystals.(Bottomright)SIRI-2flightmodelhexagonalcrystalpriortoinstallationintodetectorhousing.

MERger-eventGamma-Ray(MERGR)Telescope

Instrument performance• SensitivitytoE=20keV to2MeV𝛾-rays,with4%spectralresolutionat662keV.Largefieldofview~6sr (halfsky).

• HighdetectionefficiencyforGRBs:100%forfluence >1.5ph/cm2withinFOV(belowleft).

• Localizations,68%radiiof6deg (and