Spectral and Timing Analysis of the Prompt Emission of Gamma Ray Bursts A Thesis Submitted to the Tata Institute of Fundamental Research, Mumbai for the degree of Doctor of Philosophy in Physics by Rupal Basak School of Natural Sciences Tata Institute of Fundamental Research Mumbai Final Submission: Aug, 2014 arXiv:1409.5626v1 [astro-ph.HE] 19 Sep 2014 To my Parents Contents List of Publication viii 1 GRBs: The Extreme Transients 1 1.1 Overview ........................................ .............. 1 1.2 ThesisOrganization.. ... .... .... .... ... .... .... .. ................... 2 1.3 HistoryAndClassification . .................... 2 1.3.1 Discovery,AfterglowandDistanceScale . ...................... 2 1.3.2 ClassificationofGRBs . ................ 3 1.4 Observables..................................... ................ 7 1.4.1 PromptEmissionCharacteristics . ..................... 7 1.4.2 GenericFeaturesOfAfterglows . ................... 9 1.4.3 GeVEmission ................................... ............ 10 1.4.4 GRBCorrelations ............................... .............. 10 1.5 AWorkingModelforGRBs .... .... .... ... .... .... .... ................ 11 1.5.1 CompactnessAndRelativisticMotion . ..................... 11 1.5.2 “FireballModel”AndRadiationMechanism . ..................... 12 1.5.3 CentralEngineAndProgenitor. ................... 15 1.6 GRBResearch ..................................... .............. 16 1.7 BooksAndReviewArticles . .................. 17 2 Instruments And Data Analysis 18 2.1 Overview ........................................ .............. 18 2.2 The Swift Satellite.......................................... ........ 18 2.2.1 BurstAlertTelescope(BAT) . .................. 18 2.2.2 X-RayTelescope(XRT) . ............... 20 2.2.3 UV-OpticalTelescope(UVOT). .................. 21 2.3 The Fermi Satellite .......................................... ....... 21 2.3.1 Gamma-rayBurstMonitor(GBM). ................. 21 2.3.2 LargeAreaTelescope(LAT) . ................. 22 2.4 DataAnalaysis ................................... ................ 23 2.4.1 Swift/BAT............................................... ... 23 2.4.2 Swift/XRT............................................... ... 24 2.4.3 Fermi/GBM............................................... .. 24 2.4.4 Fermi/LAT ............................................... .. 25 2.4.5 JointAnalysisAndIssues . ................. 26 2.4.6 UseOfStatistics ............................... ............... 26 2.5 ScientificAspectsOfTheSatellites . ....................... 28 2.5.1 GRB Science With Swift .......................................... 28 2.5.2 GRB Science With The Fermi ....................................... 28 3 A New Description Of GRB Pulses 29 3.1 Overview ........................................ .............. 29 3.2 GRB090618 ....................................... ............. 29 3.3 SpectralAndTimingDataAnalysisOfGRB090618 . ....................... 30 3.3.1 TimingAnalysis ................................ .............. 31 3.3.2 Pulse-wiseSpectralAnalysis. .................... 31 3.4 ASimultaneousDescriptionofGRBPulses . ....................... 32 3.4.1 Assumptions: Pulse-wise Epeak Evolution ................................ 32 3.4.2 A3-DimensionalPulseDescription . .................... 33 3.4.3 XSPECTableModel ............................... ............. 33 3.5 TimingAnalysisUsingthe3DModel . .................... 34 ii CONTENTS iii 3.5.1 SyntheticLightcurves . ................. 34 3.5.2 DerivingTheTimingParameters. ................... 35 3.5.3 SummaryOf3DPulseDescription. .................. 38 3.6 ANewPulse-wiseGRBCorrelation . .................... 38 3.6.1 Time-integrated, Time-resolved And Pulse-wise AmatiCorrelation ................... 39 3.6.2 Correlation of Eγ,iso with Epeak,0 ..................................... 41 3.7 Pulse-wiseAmatiCorrelationRevisited . ......................... 42 3.7.1 Redshift Evolution Of The Pulse-wise Amati Correlation......................... 42 3.7.2 Possible Bias For Harder First/Single Pulse . ........................ 44 3.7.3 Comparison With The Time-integrated Correlation . ......................... 44 3.8 Summary ......................................... ............. 45 4 Alternative Spectral Models of GRB Pulses 46 4.1 Motivation...................................... ................ 46 4.2 AlternativeModelsandDataSelection . ........................ 47 4.3 ResultsofTimingAnalysis . .................... 47 4.4 SpectralAnalysis ................................ .................. 48 4.4.1 ChoiceOfTime-resolvedSpectralBins . ..................... 48 4.4.2 ResultsOfTime-resolvedSpectroscopy . ...................... 48 4.5 SummaryAndDiscussion . .... .... .... ... .... .... .... ................. 51 5 Parametrized Joint Fit 54 5.1 Overview ........................................ .............. 54 5.1.1 Time-resolvedStudyWithParametrization . ....................... 54 5.1.2 TheSpectralModels .... .... .... ... .... .... .... .. ............... 54 5.2 SampleSelection ................................. ................. 55 5.3 AssumptionsOfTheNewTechnique. .................... 55 5.3.1 AssumptionsForTheBandFunction . .................. 55 5.3.2 AssumptionsForTheBBPLModel . ................ 56 5.3.3 AssumptionsFormBBPLAnd2BBPLModels . ................. 56 5.4 Time-resolvedSpectralAnalysisofGRB081221 . ......................... 56 5.4.1 CaseI:UniformBinof3.0s . ................ 56 5.4.2 CaseII:UniformBinof1.0s. ................. 57 5.4.3 ParameterEvolution . ................ 58 5.5 ResultsOfParametrizedJointFit(GRB081221) . ......................... 59 5.5.1 AnalysisOfTheSecondPulse . ................. 60 5.5.2 AnalysisOfTheFirstPulse . ................. 62 5.5.3 ConnectingTheRisingAndFallingPart. ..................... 62 5.5.4 ThermalAndSynchrotronOrigin . .................. 63 5.6 2BBPLModel:AComparativeStudy . ................... 64 5.7 2BBPLModel:CaseStudies . .................. 64 5.7.1 I.2BBPLvs.Band ................................ ............. 64 5.7.2 II.2BBPLvs.BBPL ............................... ............. 65 5.8 ComparisonWithGRB090618. .................. 65 5.8.1 PrecursorPulse................................ ............... 66 5.8.2 SecondPulse ................................... ............. 66 5.9 StudyOfBrightestFermiGRBsWithVariableLC . ....................... 66 5.9.1 ChoiceOfTime-resolvedBins . .................. 66 5.9.2 Time-resolvedSpectralAnalysis . ..................... 66 5.9.3 FeaturesOfSpectralEvolution. .................... 68 5.10Summary ........................................ .............. 69 6 Predictions And Physical Picture 70 6.1 Overview ........................................ .............. 70 6.2 Background...................................... ............... 70 6.2.1 FeaturesOfGeVEmission. ................ 70 6.2.2 GBM-LATCorrelation . ............... 71 6.3 SampleSelectionAndAnalysisMethod . ...................... 71 6.4 AnalysisOfGRBsWithHighGeVEmission . .................... 72 6.4.1 DelayedOnsetOfTheLATLightcurve . .................. 72 6.4.2 EvolutionOfThePower-lawFlux . .................. 72 6.5 ComparisonOfHyper-fluentWithLow-LATClass . ....................... 73 6.6 ADetailedCorrelationAnalysis . ...................... 74 6.7 SummaryAndDiscussionOnGeVPrediction . ...................... 76 CONTENTS iv 6.7.1 TheCorrelation................................ ............... 76 6.7.2 ConstrainingPhysicalModels . ................... 76 6.7.3 SpectralBreakOrCut-off . ................. 76 6.7.4 DelayedOnset: EarlyIndicationOf GeVEmission . ....................... 77 6.8 AHypotheticalSituation . .................... 77 6.9 DataInTheInitialTimeBins. .................... 78 6.10 TheLowerBBInTheXRTWindow . ................. 78 6.11 ThePhysicalModel.. ... .... .... .... ... .... .... ... .................. 80 6.11.1 ListOfObservations:. .................. 80 6.11.2 ASpine-sheathJetModel: . .................. 80 6.11.3 OriginOfTheSpectralComponents . .................... 81 6.11.4 ExplanationOfTheObservations: . ..................... 82 6.12Discussion..................................... ................. 83 7 Summary and Future Directions 85 7.1 TheFirstPhaseOfTheFinalStage. ..................... 85 7.2 SummaryandConclusions . .................. 85 7.2.1 SimultaneousTimingAndSpectralDescription . ........................ 85 7.2.2 ImprovedGRBCorrelation. ................. 86 7.2.3 Alternative Models Applied To GRBs With Single Pulses ......................... 86 7.2.4 ParametrizedJointFit:The2BBPLModel . .................... 87 7.2.5 ConsequencesandPredictionsofthe2BBPLModel . ...................... 87 7.2.6 PhysicalOrigin:ASpine-sheathJet . ..................... 88 7.3 FutureDirections ................................ .................. 88 7.3.1 AnalyzingTheGBMDataToPredictTheLATData . ................... 88 7.3.2 PhysicalModelOfThePromptEmission . ................... 89 7.3.3 AfterglowObservations . ................. 89 7.3.4 CluesFromOtherObjects . ................ 89 7.3.5 GRBCorrelationUsingPhysicalModels . .................... 90 A Annexure 91 B A Few Acronyms 92 B.1 AstrophysicalObjects. .................... 92 B.2 TimingAndSpectralFeatures . .................... 92 B.3 GeneralAstronomy................................ ................. 92 B.4 InstrumentsAndMissions . ................... 92 List of Tables 1.1 ClassificationofGRBs ... .... .... .... ... .... .... ... .................. 5 1.2 CorrelationsinGRBs .............................. .................. 11 2.1 Specification of