NASA Technical Reports Server (NTRS) 20150010239: GRB 130427A: A Nearby Ordinary Monster

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otherhand,whetheralsosuchbrightGRBsare
GRB 130427A: A Nearby associatedwithSNe.Uptonow,SNehavebeen
associatedonlytounder(ormildly)energeticGRBs
inthelocaluniverse.Becauseasupernovaasso-
Ordinary Monster
ciatedwiththisburst,SN2013cq,hasbeende-
tected(14),wearenowsurethatSNearealso
associatedwithverypowerfulGRBs,notonlyto
A. Maselli,1* A.Melandri,2 L.Nava,2,3 C.G.Mundell,4 N.Kawai,5,6 S.Campana,2 S. Covino,2 lowpowerbursts[fig.S6andfigure1of(14)].
J. R. Cummings,7 G.Cusumano,1 P.A. Evans,8 G.Ghirlanda,2 G.Ghisellini,2 C.Guidorzi,9
Naiveenergeticargumentsmightsuggestthatin
S.Kobayashi,4P.Kuin,10V.LaParola,1V.Mangano,1,11S.Oates,10T.Sakamoto,12M.Serino,6
powerfulGRBs,thereisnotenoughpowerleft
F.Virgili,4 B.-B. Zhang,11 S. Barthelmy,13 A.Beardmore,8 M.G.Bernardini,2 D.Bersier,4
forastrongSN;GRB130427Adefinitivelyproves
D.Burrows,11 G.Calderone,2,14 M.Capalbi,1J. Chiang,15 P.D’Avanzo,2V. D’Elia,16,17
thatthisisnotthecase.
M.DePasquale,10D. Fugazza,2 N.Gehrels,13 A. Gomboc,18,19 R. Harrison,4 H.Hanayama,20
The overall behavior of the x-ray afterglow
J.Japelj,18J.Kennea,11D.Kopac,18C.Kouveliotou,21D.Kuroda,22A.Levan,23D.Malesani,24
lightcurvehasbeencharacterizedwiththemain
F.Marshall,13 J. Nousek,11 P.O’Brien,8 J. P.Osborne,8 C.Pagani,8K. L.Page,8 M.Page,10
contributionoftheXRTonboardSwiftandtwo
M.Perri,16,17T.Pritchard,11P.Romano,1Y.Saito,5B.Sbarufatti,2,11R.Salvaterra,25I.Steele,4
additional relevant detections from the Monitor
N. Tanvir,8 G.Vianello,15 B.Wiegand,13 K.Wiersema,8 Y. Yatsu,5 T.Yoshii,5 G.Tagliaferri2 ofAll-skyX-rayImage(MAXI)experiment(15)
inthegapbetweenthefirstandthesecondSwift-
Long-duration gamma-raybursts(GRBs) are anextremely rare outcomeofthecollapseof XRTobservations(Fig.2).Theearlylightcurve, 5555
1111
massivestarsandare typically foundinthedistantuniverse. Becauseofitsintrinsicluminosity starting from t = 260 s, is characterized by an 0000
2222
(L∼3×1053ergs persecond) anditsrelativeproximity(z =0.34),GRB 130427Areached the initially steep decay with a slope a0,x = 3.32 T 8, 8, 8, 8,
highestfluenceobserved intheg-rayband.Here, wepresentacomprehensive multiwavelength 0.17,whichisconsistentwithhigh-latitudeemis- y y y y
viewofGRB130427A withSwift,the2-meter LiverpoolandFaulkestelescopes, andbyother sion (16,17); a breakat t = 424T 8 s; and aaaa
1,x MMMM
ground-based facilities,highlightingthe evolutionoftheburstemissionfrom theprompttothe n n n n
afterglow phase. ThepropertiesofGRB 130427Aare similartothoseofthe mostluminous, 1IstitutoNazionalediAstrofisica(INAF)–IstitutodiAstrofisica oooo
high-redshift GRBs,suggestingthatacommoncentral engineisresponsible forproducing S1p5a3ziIa-9le01e46FisPiacalerCmoos,mIticaaly.(I2AINSFA)F–POalsesremrvoa,toVriioaAUstgroonLoamMicoalfdai org org org org
GRBs inboththecontemporary andtheearlyuniverse andoverthefullrangeofGRB Brera,viaE.Bianchi46,I-23807Merate,Italy.3AstroParticule g.g.g.g.
isotropic energies. etCosmologie,UniversitéParisDiderot,CNRS/IN2P3,Commis- mamamama
sariatàl'EnergieAtomiqueetauxEnergiesAlternatives/Institut eeee
Gamma-rayburst(GRB)130427Awasthe servedforaGRBbySwift.The0.02-to10-MeV deRecherchessurlesloisFondamentalesdel’Univers,Observatoire ncncncnc
brightestburstdetectedwithSwift(1),as fluencemeasuredbyKonus-Wind(8)forthemain tdueteP,arLiisv,eSrpoorboolnJnoehnPaMrisoCoriteés,UFrnainvceer.si4tyA,stLroivpehrypsoicoslRSecsieeanrccehPInasrtki-, ciecieciecie
boardothwerelslpaacsewmitihssisoenvse.rIatlwga-sraaylsodethteecbtorirgshotens-t 1em0−i3sseirogncempi−s2o,dwei(th0taos1p8e.c7trus)misp(e2a.k6i8ng+/a−t0E.01)=× 1To4k6yoBrIonwsntiltouwteHoilfl,TLeivcehrnpooloolgLy3,52R-1F2,U-1K.O5oDkeapyaarmtmae,nMtoefguPhroy-skicus,, w.sw.sw.sw.s
peak wwww
andlongestburstdetectedabove100MeV,with 1028T8keV,whereasthefluenceoftheemission Tokyo152-8551,Japan.6CoordinatedSpaceObservationand wwww
themostenergeticphotondetectedat95GeV(2). episodeat(120to250s)is∼9×10−5ergcm−2, ExperimentResearchGroup,RIKEN,2-1Hirosawa,Wako,Saitama m m m m
351-0198,Japan.7UniversityofMaryland,BaltimoreCounty/
ItwasdetectedwithFermi–Gamma-rayBurstMon- withaspectrumpeakingat∼240keV(9). oooo
CenterforResearchandExplorationinSpaceScience&Technology/ rrrr
itor(GBM)(3)atT0,GBM=47:06.42UTon27April Thiseventwasextremelybrightalsointhe NASAGoddardSpaceFlightCenter,Code661,Greenbelt,MD d fd fd fd f
2013.Hereafter,thistimewillbeourreferencetime opticalanditwasimmediatelydetectedwithvar- 20771,USA.8DepartmentofPhysicsandAstronomy,University dededede
T.TheBurstAlertTelescope(BAT)(4)onboard ious robotic telescopes. In particular, the Raptor ofLeicester,Leicester,LE17RH,UK.9DepartmentofPhysics,Uni- aaaa
0 versityofFerrara,viaSaragat1,I-44122,Ferrara,Italy.10Mullard oooo
S51w.1ifts,trwighgeenreSdwoifntcGoRmBple1t3ed04a27prAepalatntnimedes(lte)w=. rpoabrottaiclrteealdesycoaptetd=ete0c.5tedsa(1b0r)ig.hOtpotpictiaclalspcoecutnrtoesr-- SStp.aMcearSyc,ieDnocrekinLagb,oSruartroeryy,RUHn5iv6eNrsTi,tyUCKo.l1le1DgeepLaorntmdoenn,tHofolAmstbrounry- ownlownlownlownl
TheSwiftslewtothesourcestartedatt=148s copyoftheafterglowdeterminedtheredshiftto omy and Astrophysics, Pennsylvania State University, 525 DDDD
andendedatt=192s.TheSwiftUltraVioletOp- bez= 0.34(11);aUVOTUVgrism spectrum DaveyLab,UniversityPark,PA16802,USA.12Departmentof
ticalTelescope(UVOT)(5)beganobservationsat (7)was alsoacquired.Atthisdistance,therest PhysicsandMathematics,AoyamaGakuinUniversity,5-10-1
Fuchinobe,Chuo-ku,Sagamihara,Kanagawa252-5258,Japan.
t = 181 s, whereas observations with the Swift frame1-keVto10-MeVisotropicenergyisEiso= 13NASAGoddardSpaceFlightCenter,Greenbelt,MD20771,
X-rayTelescope(XRT)(6)startedatt=195s(7). 8.1×1053erg,andthepeakluminosityisL = USA.14DipartimentodiFisica“G.Occhialini,”UniversitàdiMilano-
iso
Thestructureoftheg-raylightcurverevealedby 2.7×1053ergs−1.Accordingtotheluminosity Bicocca,PiazzadellaScienza3,I-20126Milano,Italy.15W.W.
theSwift-BATinthe15-to350-keVband(Fig.1) functionofSalvaterraetal.(12),weexpectone HansenExperimentalPhysicsLaboratory,KavliInstituteforPar-
ticleAstrophysicsandCosmology,DepartmentofPhysics,and
canbedividedinthreemainepisodes:aninitial eventlikeGRB130427Aevery>60years.Inthe SLACNationalAcceleratorLaboratory,StanfordUniversity,Stanford,
peak,beginningatt=0.1sandpeakingatt= nearbyuniverse (z ≲0.4,corresponding to an CA94305,USA.16INAF/RomeAstronomicalObservatory,via
0.5s; asecond largepeak, showing acomplex ageof∼10billionyears),onlyahandfuloflong Frascati33,00040MonteporzioCatone(Roma),Italy.17Agenzia
structure with a duration of ∼20 s; and a third, GRBshavebeendetected.TheseGRBsareusual- SpazialeItaliana(ASI)ScienceDataCentre,ViaGalileoGalilei,
00044 Frascati (Roma), Italy. 18Faculty of Mathematics and
muchweakerepisodestartingatt∼120s,show- lycharacterizedbyalowoverallisotropicenergy
Physics,UniversityofLjubljana,Jadranska191000,Ljubljana,
ing a fast rise/exponential decay behavior. The (Eiso ≤ 1052 erg) and are associated with super- Slovenia. 19Centre of Excellence Space-si, Askerceva cesta 12,
overalldurationofthepromptemissionwasT novae(SNe)typesIbandIc,characterizedby 1000Ljubljana,Slovenia.20IshigakijimaAstronomicalObservatory,
90
(15to150keV)=276T5s(thetimecontaining broadspectrallinesindicatinghighexpansionve- National Astronomical Observatory of Japan, 1024-1 Arakawa,
90%ofthefluence)calculatedoverthefirst1830s locities,calledhypernovae(13).GRB130427Ais Ishigaki,Okinawa907-0024,Japan.21SpaceScienceOffice,VP62,
NASA/MarshallSpaceFlightCenter,Huntsville,AL35812,USA.
of BAT observation from T0, GBM. During the insteadapowerfulGRB,suchastheonestypically 22OkayamaAstrophysicalObservatory,NationalAstronomicalOb-
earlyphasesoftheg-rayemission,strongspectral detectedatmuchhigherredshifts(z>1,witha servatoryofJapan,3037-5Honjo,Kamogata,Asaguchi,Okayama
variabilitywasobserved(Fig.1).Amarkedspec- meanz∼2correspondingtoanageof∼3billion 719-0232.23DepartmentofPhysics,UniversityofWarwick,Co-
ventryCV47AL,UK.24DarkCosmologyCentre(DARK),NielsBohr
tral hardening was observed during the prompt years).Thedetectionofanearbyandextremely
Institute,UniversityofCopenhagen,JulianeMariesVej30,2100
main event. With a total fluence F = (4.985 T powerfulGRBgivesustheopportunitytotest, Copenhagen,Denmark.25INAF-IASFMilano,viaE.Bassini15,
0.002)×10−4ergcm−2inthe15-to150-keVband, ontheonehand,whetherthisGRBhasthesame I-20133Milano,Italy.
GRB130427Areachedthehighestfluenceob- propertiesofthecosmologicalGRBsand,onthe *Correspondingauthor.E-mail:[email protected]
48 3JANUARY2014 VOL343 SCIENCE www.sciencemag.org
REPORTS
followed by a flatter decay with index a =
1,x
1.28T0.01.Afurtherbreakatt =48T22ks
2,x
is statisticallyneeded(3.8s)toaccountforafur-
thersteepeningtoa =1.35T 0.02(allerrors
2,x
arederivedfor∆c2=2.7).
The light curves in the optical and UV de-
rivedfromtheUVOT,aswellasfromground-
based telescopes (Liverpool telescope, Faulkes
Telescope North, and MITSuME Telescopes)
areshowninFig.2.Allopticallightcurvesare
well fitted by a broken power law with a =
1
0.96 T 0.01, t ¼37:4þ4:7 ks, and a ¼
break −4:0 2
1:36þ0:01. Fittingthex-ray lightcurvetogether
−0:02
withtheopticalones,wefindthesameparam-
etersfrom26.6ksonward,buttofittheearlypart
oftheX-raylightcurve,weneedanotherpower-
lawsegmentwithaslopeof1:29þ0:02andabreak
−0:01
at 26:6þ4:5 ks (Fig. 2). Therefore, from 26.6 ks
−6:6
onward a common description of all the op-
tical,UV,andx-raybehaviorispossible,where-
asat earlier times,anextrax-ray component is
required.
Weinterprettheearlyx-raylightcurve(upto
26.6 ks) as the superposition of a standard after-
glow (forward shock emission) and either the
prolongedactivityofthecentralengineor/and
Fig.1.DetailsoftheSwiftBATlightcurveinthe15-to350-keVband.(Top)TheBATlightcurve
withabinningtimeof64ms.(Inset)TheBATlightcurveupto300s,plottedonalogintensityscale, the contribution from the reverse shock emis-
showingafastrise/exponentialdecayfeaturestartingatt∼120s.(Bottom)Thephotonindexvalues sion(18–20).After26.6ks,theopticalandx-ray
ofapower-lawmodelfittotheBATspectruminthe15to150keVenergyrange. light curves share the same behavior and decay
slopes(Fig.2),includingabreakatt ∼37ks.
break
This achromatic break is suggestive of a jet
108 break,althoughthepost-breakdecay(a =1.36)
2
is shallower than predicted in the simplest the-
ory[anincreaseindecayslope>1wouldbeex-
105 pected (21)]. This could be due to additional
components contributing to the flux, to a time
dependence of the microphysical parameters
governing the fraction of shock energy going
102
to electrons (∈) and magnetic field (∈ ), or to
e B
the fact that we observed a canonical jet not
exactly on axis, but still within the jet opening
10-1 angle(22,23).
Because the optical and the x-ray emission
belongtothesamespectralpower-lawsegment,
10-4 it is possible to constrain the characteristic fre-
quencies of the afterglow spectra, in turn con-
straining the microphysical parameters of the
10-7 relativisticshock.Additionalinformationcomes
103 104 105 106 from the high-energy g-ray emission (2). The
g-rayfluxabove100MeVpeaksat∼20s.Ifthis
emission is due to afterglow radiation, the peak
Fig.2.LightcurvesforGRB130427Aindifferentwavebands.SwiftUVandvisiblefilters(w2,m2, timeimpliesabulkLorentzfactorG ∼500(2,7).
w1,u,b,v);B,V,r′,andi′filterscorrespondtoFaulkesTelescopeNorth;r′,andi′totheLiverpoolTelescope; 0
Furthermore,thepresenceofthegiga-electonvolt
g′,r′,andi′totheMITSuMEtelescopes(7).Thescalingfactorsforthefluxdensityindifferentfiltersisshown
peaksuggestsahomogeneouscircumburstden-
intheinset;thescalingfactorforthex-raylightcurve(fluxintegratedinthe0.3to10keVrange)(7)isalso
sityprofile(24).Guidedbytheseconstraintsin
shown. The x-ray light curve also includes two MAXI data points at t = 3257 s and t = 8821 s (empty
ourchoiceofparameters,weusedtheBOXFIT
squares).Thefitperformedoverallthelightcurvesrequired24freeparameters(curvenormalizations,host
codedevelopedbyvanEertenetal.(25)tomod-
galaxyopticalfluxineachband,threetemporalslopes,andtwobreaks).Becauseofshort-termlow-level
el theafterglow. Rather than trying to performa
variabilitysuperposedtothelong-termbehaviorandpossiblyresidualinhomogeneityofopticaldatataken
fromdifferenttelescopes,weaddedinquadraturea9%systematicerrorintheopticaland5%inthex-rays. formal fit to the data, we checked whether this
Finalfityieldedc2=543.02/565degreesoffreedom.Acontributionfromthehostgalaxyhasbeentakeninto burst,withanunprecedenteddatacoverageand
account in the optical bands by fitting a constant flux of ∼ 0.01 millijansky for the reddest bands, richness,canbeinterpretedintheframeworkof
correspondingtor =21.26magastabulatedintheSloanDigitalSkySurveycatalog.Asatestof the standard model for the afterglow emission,
HG
consistency,weperformedthefitusingabrokenpowerlawfortheB,g′,r′,andi′filtersindividually. or else whether it forces us to abandon the stan-
Uncertaintiesarelarger,butwedofindthatthevaluesoft ,aswellasthedecayindicesbeforeand dardframework.Wegavemoreweighttotheop-
break
afterthebreaktime,arestillconsistent,withintheerrors,withthevaluesobtainedbytheoverallfit. ticalandhigherenergyfluxesbecausetheycarry
www.sciencemag.org SCIENCE VOL343 3JANUARY2014 49
REPORTS
mostoftheafterglowluminosity,whichisorders
ofmagnitudegreaterthantheradioflux.
Neither reverse shock nor inverse Compton
(IC)emissionareincludedinthemodel,butthis
doesnotaffectourconclusions,whichprimarily
concernthelatetimesynchrotronafterglow(7).
The synchrotron flux predicted by the model re-
produces theoptical emission and thex-ray light
curve after ∼10 ks reasonably well, whereas the
earlyx-rayfluxislikelyduetoanadditionalcom-
ponent (Fig. 3). Our model underestimates the
GeVemission,butthis,giventhelarge∈/∈ ratio,
e B
canbeduetosynchrotronSelf-Comptonemission,
asenvisaged by (2,26,27).Themodelcanalso
roughlyreproducetheradioemission(7).
Consistentwiththelightcurveanalysis,the
synchrotronfluxpredictedbythemodelreproduces
reasonablywelltheopticalandx-raypartsofthe
spectral energy distribution (SED) of the after-
glow (Fig. 4), but it underestimates the GeV
emission.Althoughthemodeldoesnotentirely
reproducethecomplexityshownbythedata,it
does capture the main features of the emission
Fig.3.Radio,optical,x-ray,andg-raylightcurvesofGRB130427A.Radiodataarefrom(31): propertiesinthepureafterglowphase.
Allmeasurementsaretakenat6.8GHzexceptthelaterone,at7.3GHz.X-raydataarethesamereported Overall,thepropertiesofGRB130427Aare
inFig.2(7).LATg-raydataarefrom(2).Correspondingmodelpredictionsadoptadescriptionintermsof similartothoseofthepowerfulGRBstypically
thevanEertenetal.model(25).Toproperlyfittheradiodata,onlyafractionoftheelectronsmustbe seenatz∼1−2[acomparisonisavailablein
acceleratedafter∼70ks(tableS10)[discussionisavailablein(7)]. (7)].ThisisthemostpowerfulGRBatz<0.9.
Itobeysthespectralenergycorrelations,suchas
theE −E (28)correlationandtheE −
peak iso peak
L (29)correlation.Interpretingasajetbreak
peak
thebreakobservedat∼37ksmakesGRB130427A
consistentwiththecollimationcorrectedenergy–
-2 0 2 4 6
peak energy correlation (7, 30). GRB 130427A
-4 is also associated with a supernova, extending
the GRB-SN connection also to such powerful
52
and high-z bursts. GRB 130427A stands as an
exceptional example indicating that a common
engine is powering these huge explosions at all
-6
powers, and from the nearby to the very far,
50 earlyuniverse.
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-8 1. A.Masellietal.,GRBCoordinatesNetwork14448,
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The First Pulse of the Extremely Bright 100photonss–1cm–2inthe10to1000keVrange
andthefluence,integratedoverthesameenergy
GRB 130427A: A Test Lab for rangeandatotaldurationof~350s,is(2.4T
0.1)×10−3ergcm–2.Thelongestcontinuously
runningGRBdetector,KonusontheWindspace-
Synchrotron Shocks
craft,hasbeenobservingtheentireskyfornearly
18 years, and only one burst had a larger peak
flux,by~30%(GRB110918A)(5).GRB130427A
R. Preece,1* J. MichaelBurgess,2*A. vonKienlin,3* P.N.Bhat,2 M.S.Briggs,2 D.Byrne,4 isthemostfluentburstintheerastartingwiththe
V.Chaplin,2W.Cleveland,5A.C.Collazzi,6,7V.Connaughton,2A.Diekmann,8G.Fitzpatrick,4 1991 launch of the Burst and Transient Source
S. Foley,4,3 M.Gibby,8M. Giles,8 A. Goldstein,6,7 J. Greiner,3 D.Gruber,3 P.Jenke,2 Experiment(BATSE)ontheComptonGamma-
R. M.Kippen,9 C.Kouveliotou,6S. McBreen,4,3 C.Meegan,2 W. S.Paciesas,5V. Pelassa,2 RayObservatory.Finally,theenergyofthespec-
D.Tierney,4 A. J. van der Horst,10 C.Wilson-Hodge,6 S.Xiong,2 G.Younes,5,6 H.-F. Yu,3 tralpeakinthefirsttimebin(T –0.1to0.0s),
0
M.Ackermann,11M.Ajello,12M.Axelsson,13,14,15L.Baldini,16G.Barbiellini,17,18M.G.Baring,19 5400 T 1500 keV, is the second highest ever
D.Bastieri,20,21R.Bellazzini,22E.Bissaldi,23E.Bonamente,24,25J.Bregeon,22M.Brigida,26,27 recorded(6).
P. Bruel,28 R. Buehler,11 S. Buson,20,21 G.A. Caliandro,29 R. A.Cameron,30 P.A. Caraveo,31 Theinitialpulse(Fig.1),lastingupto2.5s
C.Cecchi,24,25E.Charles,30A.Chekhtman,32J.Chiang,30G.Chiaro,21S.Ciprini,33,34R.Claus,30 after the trigger, stands on its own as being so
J. Cohen-Tanugi,35 L.R. Cominsky,36 J. Conrad,37,14,38,39 F.D'Ammando,40 A.de Angelis,41 bright(170T10photonss–1cm–2peakfluxfor
F.de Palma,26,27 C.D.Dermer,42*R. Desiante,17 S. W.Digel,30L. DiVenere,30 P.S.Drell,30 10to1000keVinthe64-mstimebinatT +0.51s)
0
A.Drlica-Wagner,30C.Favuzzi,26,27A.Franckowiak,30Y.Fukazawa,43P.Fusco,26,27F.Gargano,27 astoberankedamongthe10brightestGBMor
N.Gehrels,44S.Germani,24,25N.Giglietto,26,27F.Giordano,26,27M.Giroletti,40G.Godfrey,30 BATSEbursts(7–9).Thebrightnessallowsusto
J.Granot,45I.A.Grenier,46S.Guiriec,44,7D.Hadasch,29Y.Hanabata,43A.K.Harding,44 trackthespectralevolutionoftherisingportion
M.Hayashida,30,47S.Iyyani,14,15,37T.Jogler,30G.Jóannesson,48T.Kawano,43J.Knödlseder,49,50 ofawell-separatedpulsewithunprecedentedde-
D.Kocevski,30M.Kuss,22J.Lande,30J.Larsson,15,14S.Larsson,37,14,13L.Latronico,51F.Longo,17,18 tail (10).Evident in theGBM low-energy light
F.Loparco,26,27 M.N.Lovellette,42 P.Lubrano,24,25 M.Mayer,11 M.N.Mazziotta,27 curve[Fig.1;aswellasthe15to350keVlight
P. F.Michelson,30 T.Mizuno,52 M. E.Monzani,30 E. Moretti,15,14A. Morselli,53 S.Murgia,30 curvepresentedin(11)]arefluctuationsstarting
R.Nemmen,44E.Nuss,35T.Nymark,15,14M.Ohno,54T.Ohsugi,52A.Okumura,30,55N.Omodei,30* ataround1sthatarenotpresentathigherener-
M.Orienti,40D.Paneque,56,30J.S.Perkins,44,57,58M.Pesce-Rollins,22F.Piron,35G.Pivato,21 gies. If these represent additional low-energy
T.A.Porter,30J.L.Racusin,44S.Rainò,26,27R.Rando,20,21M.Razzano,22,59S.Razzaque,60 pulses,theirpresenceclearlydoesnotdominate
A. Reimer,23,30 O. Reimer,23,30 S.Ritz,59 M.Roth,61 F.Ryde,15 A. Sartori,31 J. D.Scargle,62 theanalysespresentedbelow.
A.Schulz,11C.Sgrò,22E.J.Siskind,63G.Spandre,22P.Spinelli,26,27D.J.Suson,64H.Tajima,30,55 Paststudiesoftime-resolvedspectraofsim-
H.Takahashi,43 J. G.Thayer,30 J. B. Thayer,30 L.Tibaldo,30 M.Tinivella,22 D.F.Torres,29,65 plepulsesinGRBsindicatethattherearebroadly
G. Tosti,24,25 E.Troja,44,66 T.L. Usher,30 J.Vandenbroucke,30 V.Vasileiou,35 G.Vianello,30,67 twoclassesofspectralevolution.Thesearecalled
V.Vitale,53,68 M.Werner,23 B.L. Winer,69 K.S. Wood,42 S.Zhu66 “hard-to-soft”and“tracking”pulses(12,13),de-
pendingonwhethertheenergyofthepeakinthe
Gamma-ray burst(GRB) 130427Aisoneofthemost energeticGRBs ever observed. Theinitial nFn spectrum (generically called Epeak herein)
pulseupto2.5secondsispossiblythebrightestwell-isolatedpulseobservedtodate.Afinetime monotonicallydecaysindependentlyoftheflux
resolutionspectralanalysisshowspower-lawdecaysofthepeakenergyfromtheonsetofthepulse, evolution or else generally follows therise and
consistent withmodelsofinternalsynchrotronshockpulses.However,astronglycorrelated falloftheflux.Typically,thereareatmostoneor
power-lawbehavior isobserved betweentheluminosity andthespectral peakenergythatis twospectraavailableforfittingduringtherising
inconsistent withcurvatureeffectsarisingintherelativistic outflow.Itisdifficultforanyofthe portionofthefluxhistory.Whatmakesthisevent
existingmodelstoaccountforalloftheobservedspectralandtemporalbehaviorssimultaneously. uniqueisthatthereareroughlysixtimebinswith
excellentcountsstatisticsbeforethepeakinthe
In the context of Gamma-ray burst (GRB) RaySpaceTelescopeon27April2013atT = 10to1000keVflux.
0
130427A,whichtriggeredtheGamma-Ray 07:47:06.42UTC(2–4)isanextremecase.The AsseeninFig.1,thereisacleartrendinthe
BurstMonitor(GBM)(1)ontheFermiGamma- peak flux on the 64-ms time scale is 1300 T individualdetector’slightcurves:the>20MeV
www.sciencemag.org SCIENCE VOL343 3JANUARY2014 51
GRB 130427A: A Nearby Ordinary Monster
A. Maselli et al.
Science 343, 48 (2014);
DOI: 10.1126/science.1242279
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