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PDF (Thesis020605.Pdf) Optical Pulse-Phased Observations of Faint Pulsars with a Phase-Binning CCD Camera Thesis by Brian Kern In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy ITUTE O ST F N T I E C A I H N N R 1891 O O L F O I G L Y A C California Institute of Technology Pasadena, California 2002 (Submitted May 29, 2002) ii c 2002 Brian Kern All Rights Reserved iii Abstract We have constructed a phase-binning CCD camera optimized for optical observations of faint pulsars. The phase-binning CCD camera combines the high quantum efficiency of a CCD with a pulse-phased time resolution capable of observing pulsars as fast as 10 ms, with no read noise penalty. The phase- binning CCD can also operate as a two-channel imaging polarimeter, obtaining pulse-phased linear photopolarimetric observations. We have used this phase-binning CCD to make the first measurements of optical pulsations from an anomalous X-ray pulsar. We measured the optical pulse profile of 4U 0142+61, finding a pulsed fraction of 27%, many times larger than the pulsed fraction in X-rays. From this observation, we concluded that 4U 0142+61 must be a magnetar, an ultramagnetized neutron star (B>1014 G). The optical pulse is double-peaked, similar to the soft X-ray pulse profile. We also used the phase-binning CCD to obtain the photometric and polarimetric pulse profiles of PSR B0656+14, a middle-aged isolated rotation-powered pulsar. The optical pulse profile we measured significantly disagrees with the low signal-to-noise profile previously published for this pulsar. Our results show that the optical flux is entirely pulsed, with optical peaks at phases 0.2 and 0.8 with respect to the radio peak, and a bridge of emission between the peaks. The significance of the detection of pulsed polarized flux is low, but the position angles match the extrapolation of the radio polarization profile. The optical data, both photometric and polarimetric, are consistent with the polar cap model of pulsar magnetospheric emission. The fit of the optical data with the competing emission model, the outer gap model, has not yet been determined. We have developed a number of statistical tools, both to estimate the errors in our measurements and to identify systematic errors present in the pulse profiles. The statistical tools, when applied to the data presented here, show that the systematic errors are negligible, bolstering the claims of significance of these results. iv Acknowledgements An instrumentation project, by necessity, involves a number of people who contribute labor, insight, and support, in significant ways that often go unthanked and unrewarded. The person most de- serving of thanks and rewards is Steve Kaye. As an engineer, Steve was not only responsible for a significant effort in designing the electronics that make this instrument get up and go, but also for providing an extra hand when aligning optics, an extra eye when analyzing noise, whether it be on an oscilloscope or, just as likely, generated by the data analysis software itself, an extra ear when trying to sort through complex problems, and an undiscriminating palate when trying to feed our- selves at 4 a.m. the night before packing up to drive to Palomar. For that matter, he also provided his own hallucinations during long, cold winder observing runs. Steve has always been willing to fill whatever roles are in need of filling, and has always stepped up to the task when asked to do so. Perhaps even more importantly, he has been as agreeable and entertaining a friend as I could hope for, whose value cannot be underestimated when trying to keep up the battle after years upon years of failure to get data. Steve deserves everything I can thank him for and more. My advisor, Chris Martin, has provided the idea, the motivation, the support, and the encour- agement to make this project happen, from before the time I even arrived on the scene. He has never lost faith in my abilities and my good sense, even long after I have lost that same faith. With a small number of words, he has been able to maintain my self-confidence and my desire to see this project through. From its inception (as a three-month side project) through the excitement of finally getting real data, Chris has provided the calm dedication and conviction that this would eventually bear fruit. But most importantly, when I am frustrated that things aren’t coming along as I had hoped, Chris shares his understanding that these things are hard; in fact, if they weren’t hard, somebody else would have already done it. Many of the people that provide the support needed to keep this project moving never receive any feedback at all. The machinists in the Physics Shop deserve an enormous amount of credit and thanks for putting up with me when I want something by, “hmm ... How about tomorrow?” Just as important, the friendly and supportive environment provided when I’m working in the shop along with them is another way this project kept moving along. Rick, Terry, Richard, Armando, Ram´on, Isaac, Stan, Jos´e, Phil, and Nathaniel deserve far more credit than they generally receive for Caltech continuing to plod along in its pursuit of new goodies. Likewise, without the Palomar Observatory staff making that big telescope swing when we ask it to, without dropping our instrument, none of this would mean anything. v Through my embarrassingly long stay as a grad student at Caltech, a number of people have donated pieces of themselves to my experience here. My contemporaries, Brad Behr, Ben Oppen- heimer, Roy Gal, Marc Kushner, and Andrew Baker, were good people to share offices and years with as we assimilated into Caltech life. Dave Schiminovich, Ryan McLean, John Klemic, Mark Mechtlen, and Rev. Jim have been daily components of my more recent years’ experience, and have all added something extra to my understanding or enjoyment, or both. Dave deserves enormous thanks for donating a week of sleepless days and nights in our largely unsuccessful Chile camapaign. I have Bob Rutledge to thank for teaching me everything there is to know about X-ray astronomy (or, at least, everything I know about X-ray astronomy). Professional associations aside, my deep personal thanks go to to my father, who armed me with a solid education and instilled in me the self-confidence and the drive to find my own way in this world. His unswerving confidence in me was the extra push I needed at several points in my wanderings. More importantly, he taught me that it doesn’t mean much unless you enjoy life along the way. I wish there were a way to share my feelings with my mother, and for her to know I’ve followedinherfootsteps. I also single out my brother for credit, for the odd reason that I always want to tell him interesting things about what I’m working on. Is that brotherly or just competitive? Despite the magnitude of thanks I owe to everyone else, the one person to whom I owe the biggest debt is Genna, my fianc´ee. Every single night of every year, whether I was frustrated by mechanical or software problems, returning from observing through clouds or 5 arcsec seeing, Genna welcomed me home and warmed my heart. It is not possible for me to imagine making it through every day without the uncomplicated love she shows me. vi Contents Abstract iii Acknowledgements iv 1 Introduction 1 1.1OpticalPulsarObservations................................ 1 1.2ScientificFramework.................................... 3 1.3HistoryofThisEffort................................... 5 1.4OrganizationoftheThesis................................. 7 2 Instrumentation 8 2.1 Principles of Operation . 8 2.1.1 Phase Binning . 8 2.1.2 Timing....................................... 9 2.1.3 Systematic errors . 11 2.1.4 Polarization capabilities . 13 2.1.5 Nonperiodicshort-exposureimaging....................... 14 2.2Optical/Mechanical..................................... 16 2.2.1 Overview...................................... 16 2.2.2 Wide-fieldopticallayout.............................. 17 2.2.3 Dual-channelpolarimeteropticallayout..................... 18 2.2.4 Thermal....................................... 20 2.3Electronics......................................... 20 2.3.1 Overview...................................... 20 2.3.2 GPSSystem.................................... 20 2.3.3 DAQSystem.................................... 22 2.3.4 CCDLogicSystem................................. 22 2.3.5 CameraHead.................................... 23 2.3.6 CCD......................................... 25 2.4Software........................................... 25 2.5Performance......................................... 28 vii 3 Data Analysis 31 3.1BiasandFlat-FieldCorrection.............................. 31 3.2 Error Estimation and Statistics of Correlated Image Wander . 38 3.3StatisticsofPolarization.................................. 48 3.4StatisticsofPulsedFraction................................ 53 4 4U 0142+61 57 4.1 Nature paper on 4U 0142+61 . 57 5 PSR B0656+14 64 5.1 Astrophysical Journal submission on PSR B0656+14 . 64 5.1.1 Introduction.................................... 65 5.1.2 Observations.................................... 66 5.1.3 Dataanalysis.................................... 67 5.1.4 Discussion...................................... 70 5.2EmissionModels...................................... 76 6 Low-Mass X-ray Binaries and Cataclysmic Variables 80 7 Conclusions 82 Appendix A 84 Bibliography 101 viii List of Figures 2.1 CCD illumination schematic . 9 2.2Wide-fieldphaseoffsetandditherschematic....................... 13 2.3 Polarization illumination
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