The Pennsylvania State University The Graduate School Department of Astronomy and Astrophysics X-RAY AND OPTICAL EMISSION FROM NEUTRON STARS AND PULSAR WIND NEBULAE A Thesis in Astronomy and Astrophysics by Oleg Kargaltsev °c 2004 Oleg Kargaltsev Submitted in Partial Ful¯llment of the Requirements for the Degree of Doctor of Philosophy December 2004 We approve the thesis of Oleg Kargaltsev. Date of Signature George G. Pavlov Professor of Astronomy and Astrophysics Thesis Adviser Chair of Committee William N. Brandt Professor of Astronomy and Astrophysics John A. Nousek Professor of Astronomy and Astrophysics Renee D. Diehl Professor of Physics Gordon P. Garmire Evan Pugh Professor of Astronomy and Astrophysics Lawrence W. Ramsey Professor of Astronomy and Astrophysics Head of the Department of Astronomy and Astrophysics iii Abstract This dissertation is devoted to X-ray and optical-UV observations of Neutron Stars (NSs) and Pulsar-Wind nebulae (PWNe). I begin with Introduction (Chapter 1) where I briefly review the astrophysics of pulsars, their winds and synchrotron radiation. I also present an overview of the results of previous X-ray and optical observations of pulsars and PWNe which are relevant to the content of the dissertation. To provide a broader (and more complete) view of the NS population, I then describe observational properties of its more exotic representatives (e.g., Anomalous X-ray Pulsars and Central Compact Objects in Supernova Remnants), many of which have emerged only recently. Part I of the dissertation describes the UV and X-ray observations of the famous Vela pulsar and its spectacular PWN (Chapter 2). The observations which I analyzed were carried out with the Chandra X-ray Observatory and Hubble Space Telescope. I begin by presenting the spectrum and lightcurves of the pulsar as they are seen in di®erent bands of electromagnetic radiation. I then turn to imaging observations of the Vela PWN. Thirteen observations of the Vela PWN with Chandra, spanning a period of 3 years, reveal its complex and variable structure which consists of arcs, jets, knots and di®use emission. Especially interesting is the long external jet which changes its shape on a timescale of weeks and contains blobs moving at speeds of (0.5-0.6)c. In addition to the ¯ne structure of the inner PWN, a much larger and fainter asymmetric X-ray nebula emerges in the deep summed images. The shape of this outer PWN is similar to that of the radio PWN. I also present the high-resolution spectral map of the Vela PWN and compare its X-ray properties with those of other PWNe. To see if other PWNe are alike and to study the connection between the pulsar and the PWN properties, I retrieved data on rotation-powered pulsars and PWNe from the Chandra archive. Using these data, I performed a uniform statistical analysis of the PSR/PWN X-ray properties. The results, which potentially provide powerful diagnostic of the energetics and emission mechanisms of neutron stars, are presented in Chapter 3. Part II focuses on the individual observations of two middle-aged pulsars (Gemiga and B0656+14; Chapters 4 and 5), very old millisecond pulsar J0437¡4715 (Chapter 6), and the enigmatic central source in the Supernova Remnant G266.2¡1.2 (Chapter 7). The observations were carried out with HST and Chandra. For each of these objects, I describe the observation setups, data reduction, quantitative results (e.g., fluxes, spectra, light curves) and their astrophysical implications (e.g., origin of the observed radiation, NS surface temperature, connection between the X-ray and optical radiation). iv Table of Contents List of Tables :::::::::::::::::::::::::::::::::::::: vii List of Figures ::::::::::::::::::::::::::::::::::::: viii Acknowledgments ::::::::::::::::::::::::::::::::::: xvi Chapter 1. Introduction :::::::::::::::::::::::::::::::: 1 1.1 Rotation-powered pulsars and pulsar-wind nebulae (PWNe). 1 1.1.1 Essential pulsar/PWNe physics. 2 1.1.2 Synchrotron radiation. 5 1.1.3 X-ray, optical and radio observations of PWNe. 7 1.2 X-ray and optical spectra of rotation-powered pulsars. 11 1.2.1 Overview of X-ray spectra. 11 _ 1.2.2 Luminosities of pulsars and PWNe. LX ¡ E relations. 12 1.2.3 Overview of optical spectra of pulsars. 13 1.2.4 Connection between the X-ray and UV/optical properties. 14 1.3 Diversity of NS population . 14 1.3.1 Radio-Quiet Neutron Stars . 14 1.3.2 AXPs and SGRs . 16 1.3.3 Central Compact Objects in SNRs. 17 1.3.4 Hypotheses on the nature of CCOs. 18 I Young pulsars and Pulsar Wind Nebulae. 20 Chapter 2. The Vela pulsar and its Pulsar Wind Nebula. ::::::::::::: 22 2.1 Earlier X-ray and optical observations and their results. 22 2.2 Chandra observations of the Vela pulsar. 23 2.2.1 Observations and data reduction. 24 2.2.2 X-ray spectrum and pulsations. 24 2.3 HST observations of the Vela pulsar. 27 2.3.1 Observations and data reduction. 27 2.3.1.1 NUV photometry. 28 2.3.1.2 FUV spectrum. 30 2.3.2 Broad-band optical-UV spectrum. X-ray connection. 34 2.3.2.1 Timing. 34 2.3.3 Summary. 37 2.4 Chandra observations of the Vela PWN. 40 2.4.1 Observations and data reduction. 40 2.4.2 Inner PWN: Structure (arcs, jets, knots). Variability. Spectra. Models. 42 v 2.4.3 The Outer Jets of the Vela pulsar. 53 2.4.3.1 Spatial variation . 54 2.4.3.2 Spectrum and luminosity . 57 2.4.3.3 Geometry . 65 2.4.3.4 Magnetic ¯eld and energetics . 69 2.4.3.5 End bend and outer PWN: E®ect of SNR wind? . 72 2.4.3.6 Loop-like structures and blobs: Instabilities in pinched flow? . 73 2.4.3.7 Summary and Conclusions . 74 2.4.4 Global structure of the Vela PWN in X-rays . 76 2.4.4.1 Deep X-ray images . 76 2.4.4.2 Photon index maps . 80 2.4.4.3 Comparison with the Crab PWN. 81 2.5 Vela PWN in radio and optical: The multiwavelength picture. 86 2.5.1 Radio PWN . 86 2.5.2 Comparison between the radio and X-ray PWNe morphologies. 86 2.5.3 Search for a compact optical nebula . 86 2.5.4 Search for an extended nebula . 92 2.5.4.1 Implications of non-detection of optical PWN. 92 2.5.5 Multiwavelength spectrum of the Vela PWN . 95 2.6 Observational perspectives. Optical, X-ray and radio polarimetry. 98 Chapter 3. Chandra observations of pulsars and PWNe. ::::::::::::: 99 3.1 Overview of the observations. Data reduction. 99 3.1.1 Images. 99 3.1.2 Spectra. 103 3.2 Correlations between pulsar and PWNe properties. 104 II Thermal and magnetospheric emission from neutron stars. 109 Chapter 4. HST and XMM observations of the Geminga pulsar. :::::::: 111 4.1 Introduction. 111 4.2 Previous observations of Geminga. 111 4.3 Optical/UV observations with HST . 112 4.3.1 Photometry with STIS/NUV-MAMA. 112 4.3.2 FUV Spectrum. 115 4.3.3 NIR through FUV spectrum . 121 4.3.4 Timing analysis of NUV and FUV data. 125 4.4 X-ray spectrum and pulsations of Geminga . 128 4.4.1 X-ray spectrum . 128 4.4.2 X-ray pulsations . 131 4.5 Discussion . 134 4.5.1 Thermal component(s) of the Geminga's spectrum . 134 4.5.2 Pulsations in thermal emission . 139 vi 4.5.3 Nonthermal emission of Geminga . 141 4.6 Summary and conclusions . 142 Chapter 5. HST observations of PSR B0656+14. ::::::::::::::::: 144 5.1 Previous observations. 144 5.2 STIS/FUV-MAMA observation. 145 5.2.1 FUV Spectrum. 145 5.2.2 Timing analysis. 147 5.3 Broadband optical-UV spectrum. Summary. 148 Chapter 6. HST observations of the millisecond pulsar J0437¡4715. :::::: 151 6.1 Optical observations of millisecond pulsars. 151 6.2 HST Observation . 152 6.3 Data reduction. 153 6.4 Neutron star or white dwarf? . 160 6.4.1 Thermal origin of the FUV spectrum. Broadband Spectrum. 160 6.5 Heating mechanisms. 163 6.5.1 Internal heating . 163 6.5.2 External heating . 165 6.6 Are millisecond pulsars hotter than ordinary old neutron stars? . 166 6.7 Possible spectral line at 1372 Aº . 168 6.8 Magnetospheric component in J0437 spectrum . 169 6.9 Summary and conclusions . 169 Chapter 7. Chandra observations of CCO J0852¡4617. ::::::::::::: 171 7.1 Previous observations. 171 7.2 Chandra observations and data reduction. 172 7.3 Spectrum. 172 7.4 Timing. No pulsations? . 173 7.5 The nature of CCO in G266.2{1.2 . 175 7.5.1 Accretion-powered X-ray pulsar? . 175 7.5.2 Isolated cooling neutron star? . 177 7.6 Conclusion. 178 Chapter 8. Overview and summary. :::::::::::::::::::::::: 179 Bibliography :::::::::::::::::::::::::::::::::::::: 182 vii List of Tables 2.1 Parameters of the two-component ¯ts to the Vela pulsar spectrum for HRC-S/LETG and ACIS/HETG-CC data. The radii and luminosities are for a distance of 300 pc. 25 2.2 Parameters of the two-component ¯ts to the Vela pulsar spectrum for ACIS-CC data. The radii and luminosities are for a distance of 300 pc. 25 2.3 FUV-MAMA counts and fluxes in ¸-bins . 33 2.4 Summary of Chandra observations of the Vela PWN. 40 2.5 Shifts applied to the ACIS images to improve their alignment. 42 2.6 Spectral parameters and surface brightnesses for the ACIS observations of the the outer jet. 64 2.7 Available optical datasets for the Vela pulsar ¯eld.