Giugno2007 Modelandsimulationofgamma-raypulsaremissioninGLAST CorsodiDottoratoinFisicaXIXCicloTesidiDottorato SCUOLADIDOTTORATOGALILEOGALILEI Universit`adiPisa

Universit`

a di Pisa

Facolt`

a di Scienze Matematiche Fisiche e Naturali

SCUOLA DI DOTTORATO GALILEO GALILEI

Corso di Dottorato in Fisica XIX Ciclo

Tesi di Dottorato

Model and simulation

of gamma-ray pulsar emission

in GLAST

Candidato

Relatore

Massimiliano Razzano

Prof. Ronaldo Bellazzini

Contents

1 GLAST and the gamma-ray Universe 9

1.1 Explorers of the gamma-ray sky . . . 10

1.2 Gamma rays from the sky . . . 12

1.3 Active Galactic Nuclei and blazars . . . 13

1.4 Gamma-ray Pulsars . . . 16

1.5 Supernova Remnants and Interstellar Medium: the physics of Cosmic Rays 18 1.6 The Galactic Center . . . 19

1.7 Gamma Ray Bursts . . . 21

1.8 Solar flares . . . 22

1.9 Gamma-ray background and Extragalactic Background Light . . . 23

1.10 New Particle Physics . . . 24

1.11 Unidentified Sources . . . 25

1.12 GLAST and Ground-Based Telescopes . . . 28

1.13 Summary . . . 29

2 The GLAST Large Area Telescope 30 2.1 Before GLAST: the Compton Gamma Ray Observatory . . . 31

2.1.1 The EGRET telescope . . . 32

2.2 The LAT scientific-driven requirements . . . 33

2.3 Overview of the Large Area Telescope . . . 35

2.4 The LAT Calorimeter . . . 38

2.5 The LAT Tracker . . . 39

2.5.1 Structure of the Tracker . . . 41

2.6 The LAT Anticoincidence detector . . . 43

2.7 Data Acquisition System and Trigger . . . 45

2.7.1 The LAT Trigger . . . 45

2.8 LAT expected performances . . . 46

2.9 MonteCarlo simulations of the LAT . . . 47

2.10 The GLAST Science Analysis Environment . . . 50

2.10.1 Data Format . . . 50

2.10.2 Science Tools . . . 52

2.11 LAT status . . . 52

2.12 Summary . . . 53

CONTENTS ₃

3 Pulsars as Neutron Stars 54

3.1 The discovery of pulsars . . . 54

3.2 Neutron Stars . . . 56

3.2.1 Mass and radius . . . 57

3.2.2 Structure . . . 58

3.3 Spin down in pulsars . . . 58

3.3.1 Age estimates . . . 61

3.3.2 Birth period . . . 61

3.3.3 Magnetic field strength . . . 61

3.4 Neutron star populations . . . 62

3.5 Radio emission from Pulsars . . . 64

3.6 Optical emission . . . 65

3.7 High-energy emission . . . 67

3.8 Summary . . . 68

4 Gamma-ray emission from pulsars 69 4.1 Gamma-ray pulsars: an observational approach . . . 69

4.1.1 Pulse profiles . . . 71

4.1.2 Spectral features . . . 72

4.1.3 Gamma-ray pulsars compared with radio pulsar population . . . . 73

4.2 Basic theory of pulsar magnetospheres . . . 73

4.2.1 The need for a magnetosphere . . . 74

4.2.2 The Goldreich-Julian magnetosphere . . . 75

4.2.3 Discussion of the Goldreich-Julian model . . . 77

4.3 Models for gamma-ray emission . . . 78

4.3.1 Polar Cap models . . . 78

4.3.2 Gamma-rays from polar caps . . . 80

4.4 Outer Gap models . . . 82

4.4.1 Gamma-rays from Outer Gaps . . . 83

4.5 GLAST and γ-ray pulsars science . . . 85

4.5.1 Polar Cap or Outer Gap models? . . . 85

4.5.2 How many γ-ray pulsars? . . . 88

4.6 Summary . . . 88

5 Pulsar Simulation Tools for GLAST 90 5.1 Overview of PulsarSpectrum . . . 91

5.1.1 Input Parameters . . . 92

5.1.2 Simulator Engine and Timing effects . . . 93

5.1.3 Output products and MonteCarlo simulation of the LAT . . . 93

5.2 PSRPhenom, the Phenomenological Model . . . 94

5.3 PSRShape, simulating complex emission scenarios . . . 98

5.4 Photon extraction from the source . . . 100

5.5 Timing corrections . . . 102

5.5.1 Barycentric Effects . . . 103

5.5.2 Period changes and ephemerides . . . 105

5.6 Timing Noise . . . 106

CONTENTS ₄

5.7 Pulsars in binary orbits . . . 112

5.7.1 Keplerian description . . . 113

5.7.2 Binary corrections . . . 114

5.8 The Pulsar Simulation Suite . . . 116

5.9 Summary . . . 117

6 LAT Data Analysis: the case of EGRET pulsars 119 6.1 Pulsar Data Analysis . . . 120

6.1.1 Spatial Analysis . . . 120

6.1.2 Temporal Analysis . . . 123

6.1.3 Spectral Analysis . . . 125

6.2 Description of the EGRET pulsar Dataset . . . 126

6.3 Testing the periodicity of a bright pulsar: the case of Vela . . . 127

6.3.1 Simulated Dataset . . . 127 6.3.2 Periodicity testing . . . 129 6.4 The analysis of PSR B1706-44 . . . 132 6.4.1 Simulation of PSR B1706-44 . . . 133 6.4.2 Spatial Analysis . . . 135 6.4.3 Pulse profile . . . 135 6.4.4 Spectral analysis . . . 138

6.5 The faintest of EGRET pulsars: PSR B1951+32 . . . 141

6.5.1 Simulated dataset . . . 142

6.5.2 Spatial analysis . . . 144

6.5.3 Pulse profile . . . 145

6.5.4 Spectral analysis . . . 146

6.6 Summary . . . 147

7 Pulsar simulations for LAT Data Challenge 2 149 7.1 The LAT Data Challenges . . . 149

7.1.1 The DC2 sky model . . . 151

7.2 Pulsar Simulations for DC2 . . . 153

7.3 The EGRET pulsars . . . 153

7.4 Isolated pulsars with Slot Gap emission . . . 154

7.5 Millisecond pulsars . . . 160

7.6 3EG pulsars . . . 166

7.7 Summary . . . 167

8 Pulsar Analysis in Data Challenge 2 169 8.1 Automated Analysis Procedure for DC2 pulsars . . . 169

8.1.1 Identification of the pulsars . . . 170

8.1.2 Selection of the Region of Interest . . . 170

8.1.3 Barycentric corrections . . . 173

8.1.4 Periodicity Tests . . . 173

8.2 Pulsar Detection . . . 173

8.3 The pyPulsar Analysis Package . . . 174

8.4 Analysis of pulsars detected as point sources . . . 175

CONTENTS ₅

8.4.2 Results . . . 176

8.5 Beyond the LAT Source Catalog . . . 179

8.6 Comparing the results . . . 181

8.7 Perspectives for an optimized analysis . . . 182

8.8 Summary . . . 182

9 Polar Cap or Outer Gap: what can GLAST say? 184 9.1 Background . . . 184

9.2 Simulations and Data Analysis . . . 186

9.3 Results . . . 190

9.4 Discussion of the results . . . 195