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Nustar Observatory A study of Pulsar Wind Nebulae and non-thermal filaments with the NuSTAR observatory Melania Nynka Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Graduate School of Arts and Sciences Columbia University 2015 c 2015 Melania Nynka All rights reserved Abstract A study of Pulsar Wind Nebulae and non-thermal filaments with the NuSTAR observatory Melania Nynka NuSTAR, the first high-energy focusing X-ray telescope, has provided an unprecedented view of the high-energy universe above 10 keV. The capabilities of NuSTAR improve the sensitivity as well as the spectral and spatial resolution by factors of 10 to 100 over previous missions operating above 10 keV. I first briefly describe the fabrication and calibration campaign of the NuSTAR optics at Columbia University. I then present two main areas of research with NuSTAR: the pulsar wind nebula (PWN) G21.5-0-.9, and the investigation of several non-thermal filamentary structures within 0.5 deg. of the Galactic Center. G21.5-0.9 is a well-studied PWN, and was observed by NuSTAR with 280 ks in the first ∼ months of its mission. I determined the existence of an X-ray spectral break at 9 keV in ∼ its non-thermal PWN spectrum, which may be indicative of a complex electron injection spectrum or an additional transport mechanism such as advection. I use spatially resolved images to derive an energy-dependent cooling length scale to be L(E) E−0.21. This was ∝ applied to a magnetohydrodynamic advection transport model to determine that G21.5- 0.9 may require magnetic flux non-conservation. Image analysis involving deconvolution revealed non-thermal emission up to 20 keV, likely the supernova shell. The Cannonball is a known high-velocity neutron star escaping the radio shell of Sgr A East with an extended radio and soft X-ray tail. NuSTAR analysis revealed its non- thermal spectrum (Γ = 1.6) extending to 30 keV, a magnetic field strength of 313 ∼ − 550µG consistent with its equipartition value was derived. Next I analyzed the X-ray filament G359.97-0.038. I measured the non-thermal NuSTAR spectrum to be Γ = 1.3 ± 0.3 extending to 50 keV. Incorporating broad-band morphological and spectral data from radio (5.5 and 8.3 GHz) as well γ-ray data from the Fermi observatory, I conclude that the G359.97-0.038 is not a PWN but more likely the result of an interaction between the Sgr A East remnant and the nearby M0.02-0.07 molecular cloud. Lastly I observe the filament G0.13-0.11. Morphological and spectral information strongly suggest the object is a PWN elongated by the ram pressure from the nearby Radio Arc. Contents List of Figures iv List of Tables vii Acknowledgements viii Dedication x 1 The NuSTAR Observatory 1 1.1 NuSTAR: an overview ............................ 1 1.2 The NuSTAR Observatory .......................... 3 1.3 The NuSTAR optics ............................. 6 1.3.1 Overview and Performance ...................... 6 1.3.2 Components of the NuSTAR optics ................. 9 1.3.3 Construction ............................. 14 1.4 Rainwater Memorial Calibration facility .................. 17 2 General overview of rotation-powered pulsar wind nebulae 23 2.1 PWN basics .................................. 23 2.2 Essential pulsar physics ............................ 26 2.3 Synchrotron emission: radio to X-ray .................... 29 2.3.1 Radiation from a population of electrons .............. 32 3 PWN G21.5-0.9 Overview and Analysis 38 3.1 Previous observations of G21.5-0.9 ..................... 38 3.2 G21.5-0.9 and NuSTAR ........................... 41 3.3 NuSTAR observations and data reduction ................. 45 3.4 NuSTAR spectroscopy of the PWN ..................... 48 3.5 NuSTAR spatially resolved spectroscopy .................. 50 3.6 NuSTAR Image analysis ........................... 52 3.6.1 Image data reduction ......................... 52 i Contents 3.6.2 G21.5-0.9 PWN energy-dependent radius .............. 54 3.6.3 The North Spur and Eastern Limb ................. 55 3.6.3.1 1-D profile analysis ..................... 56 3.6.3.2 Image deconvolution: Overview .............. 57 3.6.3.3 Image deconvolution: method and verification ...... 60 3.6.3.4 Image deconvolution: analysis ............... 61 3.7 TIMING SEARCH .............................. 64 4 G21.5-0.9 Discussion 67 4.1 PWN spectral break ............................. 67 4.1.1 External causes for the spectral break ................ 68 4.1.2 Spectral break due to PWN physics ................. 72 4.2 PWN softening ................................ 74 4.3 Physical conditions inferred from cooling scale length measurements ... 75 4.3.1 Overview ............................... 75 4.3.2 Kennel and Coroniti: Canonical Advection ............. 77 4.3.3 Tang and Chevalier: Diffusion .................... 79 4.3.4 Reynolds: Radially-Dependant Advection ............. 81 4.4 The North Spur ................................ 86 4.5 The Eastern Limb: the shell of G21.5-0.9 .................. 90 5 The Cannonball: A Runaway Neutron Star from the Sgr A East SNR 94 5.1 Introduction .................................. 94 5.2 NuSTAR observations ............................ 98 5.3 Imaging analysis ............................... 98 5.4 Spectral analysis ............................... 102 5.5 Timing analysis ................................ 106 5.6 Discussion ................................... 107 5.6.1 Is the Cannonball a Pulsar? ..................... 107 5.6.2 Magnetic Field of the Cannonball PWN .............. 109 5.6.3 Magnetic Field of the Putative Pulsar ................ 114 5.7 Summary ................................... 116 6 Introduction to non-thermal filaments 117 6.1 Introduction .................................. 117 6.2 Large-scale Filaments ............................. 118 6.2.1 Origin of the magnetic field ..................... 120 6.3 Smaller-scale Filamentary structures .................... 122 6.3.1 Possible sources of emission ..................... 124 7 The curious case of X-ray filament G359.97-0.038 127 7.1 Introduction .................................. 127 ii Contents 7.2 Observations .................................. 130 7.3 Image Analysis ................................ 132 7.4 Spectral Analysis ............................... 135 7.4.1 NuSTAR hard energy X-ray spectrum ............... 135 7.4.2 Spatially-resolved spectral analysis ................. 139 7.4.3 Radio spectral analysis ........................ 140 7.5 Discussion ................................... 141 7.5.1 What is G359.97-0.038? ....................... 141 7.5.2 G359.97-0.038 as a PWN ...................... 143 7.5.3 G359.97-0.038 as a magnetic flux tube ............... 148 7.5.4 G359.97-0.038 as SNR-MC interaction ............... 149 7.6 Summary ................................... 154 8 X-ray filament G0.13-0.11 156 8.1 The NuSTAR Galactic Center Mini Survey ................. 156 8.1.1 Mini Survey Science goals ...................... 158 8.2 Introduction .................................. 161 8.3 NuSTAR Observations and Data reduction ................. 164 8.4 NuSTAR Spectral analysis .......................... 166 8.4.1 Point Source 174622.7-285218 .................... 166 8.4.2 Filament G0.13-0.11 ......................... 168 8.5 Discussion ................................... 170 8.5.1 Coincident Fermi source? ....................... 170 8.5.2 Filament G0.13-0.11 ......................... 171 Bibliography 174 iii List of Figures 1.8 A finite element analysis of the test coupons designed to replicate the stress of the innermost layers of the optic during launch. The coupons were designed to contain the same levels of tensile (a) and shear (b) stress. Figures are from Craig et al. [2011]. ..................... 13 1.9 Figures obtained from An et al. [2009]. (a) Epoxy that has been cured with- out vacuum mixing. Large and small pockets of air are visible throughout the entire sample. (b) Epoxy that has been vacuum mixed according to the NuSTAR fabrication procedure. There are no visible air pockets. (c)A side view of the mixing chamber. The epoxy is shown in yellow within the syringe. The stainless steel mixing blade, custom-designed for NuSTARis shown in an inset on the left. ........................ 14 1.12 An image of the tunnel PVC pipeline. During calibration, the pipeline is held at a vacuum pressure below 1 Torr. The diameter of the pipeline is 10 cm at the source to 50 cm at the optic. The downstream direction is∼ towards the bottom right∼ of the image. .................. 20 1.13 A top view of RaMCaF visible from the highbay. Shown in the image are the Calibration room, which houses the optics and calibration bench, the Detector room, and the 10 m of pipe that connects the two chambers. The downstream direction is towards the right of the image. .......... 20 2.2 The synchrotron spectrum of a single relativistic atom interacting with a magnetic field. The spectrum follows a power-law distribution with power law index of 1/3 until the maximum, after which the spectrum decays exponentially. The peak emission occurs at ν 0.29ν . ........ 33 max ∼ c 3.1 Figures obtained from [Matheson and Safi-Harb, 2005]. Left– Full-color image of G21.5-0.9 from Chandra ACIS data. The 40′′ nebula is seen in the center of the image, while the halo, North Spur,∼ and Eastern limb are visible at larger radii. Right– G21.5-0.9 data from Chandra. Radial variation of Γ, in an absorbed power-law model. The absorbtion column for all fits is frozen to 2.2 1022cm−2. .................... 40 × 3.3 A power-law spectrum with photon index Γ = 2.0 shown in blue, normal- ized to 1 at 1 keV. The red curve represents the same power-law spectrum with an applied absorption of N =2.99 1022 cm−3. .......... 47 H × iv List of Figures 3.7 Intensity profiles of G21.5-0.9 were obtained to confirm the existence of the Eastern Limb and North Spur in the raw NuSTAR images. Left– 3 6 keV NuSTAR mosaic image. Exposure-map vignetting corrections − were applied, and FPMA and FPMB summed. The red, green, and blue lines indicate the locations along which the profiles were obtained. Right– Intensity profiles as a function of distance (in arcseconds) from the PWN center from the NuSTAR 3 6 keV, 6 10 keV, 10 15 keV, 15 20 keV image.
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