The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

Recommendations

Info

Chapter 3 BAT Operating Modes and Data Types 3.1 Introduction The BAT flight software produces several data products. As mentioned in the previous chapter, the BAT is a photon counting instrument. That is, each photon interaction is recorded separately by the flight electronics and flight computer. However, like other missions there is not enough on-board storage or downlink capacity to send all of these events to the ground. Instead, the BAT sends full event data for special triggers (i.e. for gamma-ray bursts), and otherwise makes binned products. Normally, the BAT is searching for a new GRB trigger while in survey mode. In this mode, an energy spectrum is accumulated for each detector in the array on a time scale of approximately every 5 minutes. While this data allows an observer to recover the fluxes of sources over long time scales there are significant systematic errors that must be addressed, and have not yet been accounted for in the BAT software. After a successful trigger, several products are produced in response to a gamma-ray burst. The most significant of these is a dump of event data which brackets the trigger time, with a total duration of about 10-15 minutes. The BAT also produces several products all the time, regardless of whether there is a GRB or not. These are typically various array rates, housekeeping values, and trigger diagnostics. A more complete description of these products is presented in the rest of this chapter. 3.2 GRB Products and Response Most of the time the BAT is in survey mode. Trigger criteria are evaluated on a continuous basis. When the BAT detects a rate increase (in one of several energy bands or spatial regions), then it indicates a “rate trigger,” which in turn initiates on-board image processing to confirm a new point source. Typically, there are many rate triggers per hour, each given its own trigger number, but few are confirmed by imaging. On a periodic basis, the BAT flight software also performs image analysis independent of the rate triggering system, to search for slow rising GRBs and transients. When the BAT receives a GRB trigger the BAT and the spacecraft have a preset set of responses. The typical response process is as follows, roughly in order of the time of production: 11
12 CHAPTER 3. BAT OPERATING MODES AND DATA TYPES Figure 3.1: BAT data products for a typical GRB with a slew. BAT Rate Trigger Fast-rising GRBs lead to a rate trigger. A TDRSS “Alert” message may be sent to the ground. BAT Image Confirmation The image processing step takes several seconds. If a significant new excess is detected, then a GRB is declared, and a TDRSS position message is sent to the ground. BAT Image-only Trigger The BAT regularly performs image analysis, on roughly 1 minute, 5 minute, and snapshot-duration accumulations, looking for new sources regardless of the rate trigger status. If a new excess is detected, it may be declared a GRB or a “transient” depending on the duration. Spacecraft Slew The spacecraft may or may not slew, depending on the merit of the burst and the observing constraints. The BAT products should be the same regardless of whether or not there is a slew. However, there will only be XRT and UVOT data if the slew occurs. BAT TDRSS Light Curve The BAT produces a total rate quick-look light curve of several hundred seconds around the time of the trigger. This light curve is acceptable for looking for crude features, but cannot be trusted for sensitive analysis, since the rates are contaminated by background events. This is especially a problem during the slew, when sources pass into and out of the BAT field of view, which causes rate variations. BAT Event Data This is the most relevant and useful data for GRB analysis, since it allows background to be removed via “mask weighting.” Also, the user can choose any source position, temporal or spatial binning that they desire. GRB light curves and spectra can be extracted during the spacecraft slews as well as pointings. Note that the BAT event data may overlap in time with nearby survey intervals. The response process and products as a function of time during a GRB are illustrated in Figure 3.1. Note that even if the spacecraft does not slew, or slews to another target (not the GRB
Page 1 and 2: The SWIFT BAT Software Guide Versio
Page 3 and 4: ii CONTENTS 4.4 How Sky Fluxes are
Page 5 and 6: iv CONTENTS 6 BAT Analysis Issues 5
Page 7 and 8: vi CONTENTS D.1.6 SEE ALSO . . . .
Page 9 and 10: viii CONTENTS D.10.2 USAGE . . . .
Page 11 and 12: x CONTENTS D.18.5 EXAMPLES . . . .
Page 13 and 14: xii CONTENTS
Page 15 and 16: 2 CHAPTER 1. INTRODUCTION • Appen
Page 17 and 18: 4 CHAPTER 2. BAT INSTRUMENT Figure
Page 19 and 20: 6 CHAPTER 2. BAT INSTRUMENT Figure
Page 21 and 22: 8 CHAPTER 2. BAT INSTRUMENT The The
Page 23: 10 CHAPTER 2. BAT INSTRUMENT
Page 27 and 28: 14 CHAPTER 3. BAT OPERATING MODES A
Page 33 and 34: 20 CHAPTER 4. INTRODUCTION TO BAT A
Page 41 and 42: 28 CHAPTER 5. BAT ANALYSIS PROCEDUR
Page 69 and 70: 56 CHAPTER 6. BAT ANALYSIS ISSUES T
Page 71 and 72: 58 CHAPTER 6. BAT ANALYSIS ISSUES w
Page 73 and 74: 60 CHAPTER 6. BAT ANALYSIS ISSUES T
Page 75 and 76:
62 CHAPTER 6. BAT ANALYSIS ISSUES 2
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
70 APPENDIX A. BAT DATA FORMATS Nam
Page 85 and 86:
72 APPENDIX A. BAT DATA FORMATS A.5
Page 87 and 88:
74 APPENDIX A. BAT DATA FORMATS A.5
Page 89 and 90:
76 APPENDIX A. BAT DATA FORMATS Nam
Page 91 and 92:
78 APPENDIX A. BAT DATA FORMATS wil
Page 93 and 94:
80 APPENDIX A. BAT DATA FORMATS BBi
Page 95 and 96:
82 APPENDIX A. BAT DATA FORMATS Arr
Page 97 and 98:
84 APPENDIX A. BAT DATA FORMATS 535
Page 99 and 100:
86 APPENDIX B. BAT FITS KEYWORDS
Page 101 and 102:
88 APPENDIX B. BAT FITS KEYWORDS
Page 103 and 104:
90 APPENDIX C. BAT ACRONYM AND TERM
Page 105 and 106:
92 APPENDIX C. BAT ACRONYM AND TERM
Page 107 and 108:
94 APPENDIX D. BAT SOFTWARE TOOL RE
Page 109 and 110:
Page 111 and 112:
Page 113 and 114:
100 APPENDIX D. BAT SOFTWARE TOOL R
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
190 APPENDIX E. BAT SOFTWARE REVISI
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237:
show all

The SWIFT BAT Software Guide Version 6.3 30 ... - HEASARC - Nasa

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?