Galac%cTransientsintheMeVBand

LizHaysNASAGSFC

Galac%cVariabilityintheGeVBand•  CompactBinaries–  Gammabinaries(LS+61303,LS5039,HESSJ0632,J1018--cyclical)

– MSPs(pulsar/wind–transi%onal)–  CygnusX-3(microquasarjet)–  Novae(shock–truetransient)

•  Other–  EtaCarinae(collidingwindbinary--cyclical)

–  Crabnebulaflares(reconnec%on?--repeatsatrandom)

–  Solarflares(reconnec%on--repeatsatrandom)

Novae

NovashocksproduceGeVpar%cles

Ackermann,M.etal.2014

RadioimagingofexpandingsynchrotronemissionChomiuketal.2014

Symbio%candclassicalnovaeproducegammas

GammaCharacteris%cs

TrackingEvolu%onofShock

Metzgeretal.2015

Analogtocore-collapseSN-novaeprovidepossibilityfor%me-dependentstudyofnon-rela%vis%cshocksusingop%cal/UV/X-ray/gamma-raylightcurves.Ejectaprovidesareasonablygoodhadroniccalorimeter.

Ques%onsforMeV•  WhatistheshapeofthespectrumbelowfewhundredMeV?

–  Hadronicfavoredbutnotaclearcase–  SNRshowanevolu%onfromleptonictohadronic

•  Increaseddetec%onrate?–  ~30-35/yrexpectedintheMilkyWay.LATobserves~1/yr.Someof

thisshouldbedistance.–  Enhancedangularresolu%onandsensi%vityat~100MeVhelpfulin

makingdetec%onsinregionsofhigherGalac%cbackground•  Extendedgamma-raylightcurve

–  Hintsofextendedlightcurve,butatthresholdforLAT•  Someconclusions:

–  Sensi%vitysub-100MeVimportantforcharacterizingspectrumandexpandingpopula%on(morechancestotrackbroadbandlightcurves)

–  Angularresolu%onimportanttodis%nguishinbrighterregionsofGalaxy

CrabNebulaFlares

CrabFlares:ExtremelyRapidVariability

Buehler, R. et al. 2012, ApJ, 749, 26

Meyer, M. et al. 2013, ApJL

Crabfluxdoublesasquicklyas5-8hrs.

FermiTOO

PushingLimitsofPar%cleAccelera%on

R.Buehler

Diffuseshockaccelera%ondoesnotworkFlaresaretoofast!Par%cleenergyexceedssynchrotronlimit~160MeVStrongevidenceforreconnec%on

CrabNebula:SpectralEvolu%onSufficientsta%s%csinLATtopar%%onthespectralfitinto11binsofconstantflux(BayesianBlocksanalysis)

FlaresfromotherPWN?

•  Notcrazy,buttheCrabisaspecialobject– Extremelyhighmagne%cfield– Extremelyhighpeakenergyforsynchrotronpeak(MSH15-52peakslowerbutextendsintoMeV)

– Nearby– Knownformorphologychangesinotherbands

Ques%onsforMeV

•  Whatissub-~100MeVbehaviorofnebuladuringandfollowingflares?

•  Are/Howareflaresconnectedtolonger%mescalehardX-rayvariability?

•  WhatistheMeVvariability?– HardX-ray/songammamonitoringstudiescurrentlyhavelowsensi%vityonshort%mescales

ThoughtsfortheFuture•  Withmoderateresolu%on,goodprospectsfortransientstudiesneartheGalac%cplane–  LATvariablesourcesaremainlyiden%fied

•  IngeneralLAThasdetectedvariabilityforsourcespeakingintheLATband–nonthermalsourcestendtobevariable--goodprospectsfordiscoveriesinsourceclassesnotobservedbyLAT,e.g.SGRs/magnetars,microqusars,accre%ngpulsars

•  Angularresolu%onisausefultoolforGalac%cstudies,evenfortransients