Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1997 The ag mma-ray energy spectrum of the active galaxy Markarian 421 Jeffrey Alan Zweerink Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Astrophysics and Astronomy Commons Recommended Citation Zweerink, Jeffrey Alan, "The ag mma-ray energy spectrum of the active galaxy Markarian 421 " (1997). Retrospective Theses and Dissertations. 11761. https://lib.dr.iastate.edu/rtd/11761 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. 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For thpfGrgpuate College iii TABLE OF CONTENTS ABSTRACT xiv 1 INTRODUCTION 1 1.1 Detection of Gamma Radiation 2 1.1.1 High Energy (HE) Radiation 2 1.1.2 Very High Energy (VHE) Radiation 3 1.2 Models of Active Galactic Nuclei o 1.3 Current Scientific Issues Addressable by Gamma-Ray Astronomy 7 1.3.1 AGN Issues 7 1.3.2 Other Issues 8 1.4 Organization of Dissertation 9 2 BACKGROUND 10 2.1 High Energy Gamma-Ray Astronomy 10 2.1.1 Development of the "Imaging" Technique 11 2.1.2 Current State of VHE Gamma-ray Detectors 12 2.2 Markarian 421 15 3 DATA ACQUISITION AND PREPARATION 19 3.1 The Telescope 19 3.2 Observing Modes 20 3.3 Data Acquisition and Storage 22 3.4 Data Reduction 23 3.4.1 Pedestal Subtraction and Flat-fielding 23 3.4.2 Cleaning 24 3.4.3 Parameterization 25 3.5 Data Analysis 28 iv 4 GAINS, NOISE AND PE/DC CONVERSION 31 4.1 Direct Measurement of PE/DC Conversion 31 4.1.1 Measurement of PMT Current Gains 31 4.1.2 Measurement of Signal Transmission 32 4.1.3 Calculating the PE/DC 33 4.2 Scaling the PE/DC from 1988-89 35 4.2.1 Digital Counts in the Second Highest PMT 35 4.2.2 Total Size of Shower 39 4.2.3 Compare Total Size of Largest Events 39 4.2.4 Separating the pe/dc and the reflectivity 39 5 METHOD FOR DETERMINING ENERGY SPECTRA 43 5.1 The Standard Analysis 43 5.1.1 Parameter Cuts 44 5.1.2 Energy Estimation 49 5.1.3 Collection Area 50 5.2 The Observations 52 5.2.1 Data Preparation 52 5.2.2 Parameter Distributions for the Data 53 5.2.3 Spectrum Extraction 53 5.2.4 Calculating Fluxes 56 6 ENERGY SPECTRUM FROM MARKARIAN 421-THE FLARE 59 6.1 The Markarian Flare Spectrum-Standard Analysis 59 6.1.1 Parameter Cuts, Energy Estimate and Collection Area 60 6.2 The Observations 60 6.2.1 Data Preparation 60 6.2.2 Parameter Distributions for the Data 62 6.2.3 Spectrum Extraction 62 6.3 The Extended Analysis-Removing the Upper Distance Cut 65 6.3.1 No Upper Distance Cut 66 6.3.2 Opening Up the Pass Band 69 6.3.3 Using the x Fits to the Parameters 70 6.3.4 Fitting the Parameters with a Cubic Polynomial 70 V 6.3.5 Summary of Extended Analysis 73 7 SPECTRAL VARIABILITY OF MARKARIAN 421 7.5 7.1 Choosing the Databases 7-5 7.2 Spectral Analysis 77 7.3 Sensitivity to Spectral Cutoff 79 8 CONCLUSIONS 81 8.1 Results from this Work 81 8.2 Future Directions 82 APPENDDC A CRAB AND MARKARIAN 421 DATABASES 84 APPENDEX B CALCULATION OF THE HILLAS PARAMETERS 90 BIBLIOGRAPHY 92 vi LIST OF TABLES Table 2.1 Current catalog of detected TeV gamma-ray sources 1-5 Table 2.2 Atmospheric Cherenkov Imaging Gamma Ray Observatories as of 1996 and the sources which each have detected. Sources where a DC e.xcess was detected are included. Sources with only periodic emission are omitted 16 Table 3.1 Parameters and units calculated for each event 28 Table 3.2 Supercuts values forl995/96 29 Table 4.1 Current gains in units of 10® for 6 PMTs. Wop and G<,p are the normal operating voltage and corresponding gain. Giooo and Ggoo are the gains with the PMTs operating at lOOOV and 900V, respectively 33 Table 5.1 Supercuts values for 1988/89 44 Table 5.2 Extended Supercuts values for 1995/96 Crab Nebula data. The parameter fits are shown in the brackets 46 Table 5.3 Bin by bin flux values for the 1995/96 Crab Nebula database 58 Table 6.1 E.xtended Supercuts values for 7 May 1996 Flare from Markarian 421. The parameter fits are shown in the braickets 60 Table 6.2 Counts for the ON runs and OFF run sets. The average OFF counts, statistical errors of the OFF, and the excess are shown in the last 3 columns. Only bins with X > —0.4 are included in the totals 62 Table 6.3 Bin by bin flux values for the Flare from Markarian 421 66 vii Table 6.4 Number of events passing gamma-ray cuts, bin-by-bin, for the ON runs and each of the 5 OFF run sets. The upper distance cut has been removed and the pass band set to accept 95% of the simulated gamma rays. The last 3 columns show the average of the 5 OFF sets, the excess Non - (Noff), and the significance of the excess (cf. Eqn 5.14). The "Total" row is the sum of the number with X > -0.4 69 Table 6.5 Number of events passing gamma-ray cuts, bin-by-bin, for the ON runs and each of the 5 OFF run sets. The upper distance cut has been removed and the pass band set to accept 99% of the simulated gamma rays. The last 3 columns show the average of the 5 OFF sets, the excess Non — and the significance of the excess (cf. Eqn 5.14). The "Total" row is the sum of the number with X > —0.4 70 Table 6.6 Number of events passing gamma-ray cuts, bin-by-bin, for the ON runs and each of the 5 OFF run sets. The upper distance cut has been removed, the parameters fit with a cubic polynomial, and the pass band set to accept 99% of the simulated gamma rays. The last 3 columns show the average of the 5 OFF sets, the excess Non ~{Noff), and the significance of the excess (cf. Eqn 5.14). The '^otal" row is the sum of the number with x > —0.4 72 Table 7.1 Results of the quick analysis for the combined, high and low databases 77 Table 7.2 Energy spectra derived for different Markarian 421 data sets taken during the 1995/96 observing season 77 Table A.l Data runs used to calculate the Crab energy spectrum for 1995/96 84 Table A.2 Data runs used to calculate the Markarian 421 energy spectrum for the Flare on 7 May 1996 86 Table A.3 Data runs used to calculate the Markarian 421 energy spectrum when it was in a high state during 1995/96.